Reproduction performances and conditions of group-housed non ...

Reproduction performances and conditions 

of 

group-housed non-lactating sows 

Ph.D. thesis by 

Anne Grete Kongsted 

Department of Large Animal Sciences 

The Royal Veterinary and Agricultural University 

Ridebanevej 12, DK-1870 Frederiksberg C 

& 

Department of Agroecology 

Danish Institute of Agricultural Sciences, Research centre Foulum 

P.O. Box 50, DK-8830 Tjele 

2004

PREFACE AND AKNOWLEDGEMENTS 

The present thesis intends to meet the requirements for obtaining the Ph.D. degree from the 

Royal Veterinary and Agricultural University, Copenhagen (RVAU). Throughout the 

Ph.D. study, the undersigned has been attached to the research group Farming Systems, 

Dept. of Agroecology, Danish Institute of Agricultural Sciences (DIAS), Research Centre 

Foulum. The study has been financially supported by the Danish Research Agency. 

I would like to express my gratitude to my supervisors, senior scientist Troels Kristensen, 

Dept. of Agroecology (DIAS) and Associate Professor Sven Bresson, Dept. of Large Animal 

Sciences (RVAU) for their guidance and advice much appreciated. Very special 

thanks for co-supervision go to the head of the Farming System Group, John E. Hermansen, 

whose always constructive criticism and unfailing high spirits have been very valuable, 

especially during the last couple of months. I also wish to thank the rest of the Farming 

System Group for providing a good collegiate environment. Special thanks to Jytte 

Christensen for her excellent assistance with data processing and to Lene Kirkegaard for 

her help with Reference Manager. 

The Ph.D. study included a farm study involving 14 sow herds. I wish to thank the 14 

farmers and their co-workers for their cooperativeness, kindness and great inspiration. I 

would also like to express my gratitude to the Research Technicians Henrik K. Andersen, 

Kristine R. Hansen, Michael Hansen, Orla Nielsen, Niels H. Thomsen and Helge Yde for 

their much appreciated assistance in carrying out the data collection. 

For discussions of statistical analyses, I am very grateful to Senior Scientist Jens Henrik 

Badsberg and especially to Senior Scientist Erik Jørgensen for his great contributions to 

the statistical analyses and well-timed ‘pep-talks’. I am also grateful to Dr. Nicoline Soede 

and Dr. Wouter Hazeleger, Dept. of Animal Sciences, Wageningen University, for allowing 

me to stay in their group for two months and for sharing some of their knowledge of 

reproduction physiology with me. 

I would also like to thank the following people for valuable discussions/assistance: Ph.D. 

Marianne Bonde, Ph.D. Tine Rousing, Senior Scientist Lene J. Pedersen, Senior Scientist 

Viggo Dannielsen (all from DIAS), Lisbeth U. Hansen, Lisbeth B. Petersen, Flemming 

Thorup and Brian Fisker (all from The National Committee for Pig Production). 

Finally, a very grateful thought to all the two- and four-legged creatures at ‘Skovbakken’ 

whose calm attitudes have been an essential fountain of relaxation throughout the study, 

and especially THANK YOU, Jens, for always being there 110% - also on rainy days. 

Foulum, September 2004 , Anne Grete Kongsted

Contents 

Summary……………………………………………………………………..1 

Sammendrag (Danish)……………………………………………………….5 

Background and aim…………………………………………………………9 

Outline of this thesis………………………………………………………..13 

How does group housing vary in practice?…………………………………15 

Paper I. Effect of energy intake on pregnancy rate and litter size with 

particular reference to group housed non-lactating sows – a review………21 

Paper II. Stress and fear as possible mediators of reproduction problems 

In group housed sows: A review…………………………………………..49 

Paper III. Indicators of feed intake, fear and social stress in commercial herds with 

group housed non-lactating sows………………………………………….59 

Paper IV. Relation between reproduction performance and indicators of 

feed intake, fear and social stress in commercial herds with group housed 

non-lactating sows…………………………………………………………87 

General Discussion………………………………………………………..103 

Conclusions………………………………………………………………..109 

Appendix 1. Litter size and farrowing rate, which physiological 

processes may go wrong and why? ………………………..…………………. 111

- Summary - 

SUMMARY 

In the last decade the number of group housed non-lactating sows has been increasing in 

Europe. This is mainly caused by elevated public concern of animal welfare with changed 

legislation as a consequence. However, among herds with group housed non-lactating sows 

there is a huge variation in the reproduction results. The apparently large variation in farrowing 

rate and litter size indicates that it will be possible to improve these parameters in 

some of these herds. On this background the overall aim of this thesis was to produce 

knowledge that managers can implement in their decision-making to improve the reproduction 

performance of group housed non-lactating sows. The specific aims were to identify 

important causes for impaired reproduction performance in group housed non-lactating 

sows and to develop and evaluate indicators suitable for use in decision-making in commercial 

sow herds. 

First, a review of the literature of reproduction physiology was carried out (Appendix 1). It 

was concluded that the endocrine regulation of reproduction might be influenced by energy 

intake and stress. Since experimental studies had indicated that group housing might lead 

to unequal feed intake and social stress, the hypothesis was put forward that individual 

variation in feed intake and social stress might cause impaired reproduction performance in 

some group housed non-lactating sows. To illuminate this further, two review papers were 

written a) to consider the effect of energy intake (Paper I) as well as social stress and fear 

(Paper II) and b) to define indicators of feed intake, stress and fear suitable for use in practice. 

A study in 14 herds with different layouts and management routines was carried out to 

evaluate the defined indicators (Paper III) and to investigate whether the indicators were 

suitable to express variation in the reproduction performance of sows under practical conditions 

(Paper IV). 

Paper I 

The aim of this review was to consider whether the variation in energy intake in a group of 

non-lactating sows can influence variation in litter size and pregnancy rate in practice. 

Through a review of existing literature with main emphasis on publications after 1980, the 

effect of energy supply before mating and in pregnancy on pregnancy rate and litter size 

was discussed. Based upon experimental studies, indicating that low ranking sows may 

consume considerably less than high ranking sows (e.g. 50-80%) in group housing, it was 

suggested that the variation in feed intake in a group of restrictedly fed pregnant female 

pigs may be sufficiently severe to influence pregnancy rate and litter size. 

1

Paper II 

- Summary - 

A review of 15 experiments with group housed sows showed that there are indications that 

stress and fear might be contributing reasons for the impaired reproduction seen in some 

group housed sows. Possible initiators of stress and fear might be mixing of unfamiliar 

sows and high stocking rates. Traditional methods for assessing stress and fear are expen- 

sive and/or time consuming and therefore difficult to use in large-scale on-farm studies or 

as components in a management tool to analyse and improve the reproduction performance 

in group housed sows. Therefore, based on existing knowledge, possible indicators of 

stress and fear related reproduction problems suitable for use in practice were put forward 

in the paper. However, whether these indicators were suitable to express variation in sows 

susceptibility for a good reproduction performance under practical conditions was not 

known. 

Paper III 

Experimental studies have indicated that group housing may lead to individual variation in 

feed intake, fear and social stress. However, systematic information of between-herd and 

within-herd variation in feed intake, fear and social stress in sows group housed under 

various conditions is lacking. Most likely, this is to some extent because of a lack of suitable 

assessment methods. With the aim to evaluate indicators of feed intake, fear and social 

stress and to get insight in the level and variation in these indicators in group housed sows 

under various on-farm conditions, a farm study took place including 14 commercial herds 

followed in 11 month. The results showed that back fat, skin lesions and behavioural 

measurements might be relevant indicators of the condition of the sows regarding feed 

intake, stress and fear at herd, batch, and individual sow level in commercial herds with 

group housed non-lactating sows. For almost all indicators the variation between herds was 

larger than the variation between batches within herds. However, the largest contribution to 

the variation came from the variation between the individual sows. The between-sow 

variation in back fat at farrowing was significantly higher in herds with group feeding than 

in herds with individual feeding. The study indicated that group feeding may lead to overfeeding 

of high ranking sows and severe underfeeding of a few low ranking individuals. 

The presence of feeding stalls reduced the level of aggressions the first hour after weaning. 

Irrespective of layout, sows older than third parity were involved in most aggressions the 

first hour after mixing on the day of weaning. However, three weeks after mating and at 

farrowing, these sows had the lowest level of skin lesions indicating that any stress experienced 

by these old sows was short-lasting. In herds with no escape possibilities, first parity 

sows had the highest level of skin lesions three weeks after mating and at farrowing, 

whereas in herds with escape possibilities, second and third parity sows had the highest 

level. Herds with electronic sow feeding and large dynamic groups had the highest average 

level of skin injuries. 

2

Paper IV 

- Summary - 

Results from experimental studies suggest that group housing may lead to individual varia- 

tion in feed intake, stress and fear, which may impair the reproduction performance. How- 

ever, whether the individual variation in feed intake, stress and fear in sows group housed 

under commercial conditions is severe enough to be responsible for an impairment of the 

reproduction performance was not known. Therefore, a detailed farm study including 14 

herds with different layouts and management routines was carried out and the relations 

between various indicators of feed intake, stress and fear and reproduction performance 

were studied. Positive correlations between back fat gain from weaning to three weeks 

after mating and chance of pregnancy (P

- Sammendrag - 

SAMMENDRAG 

Antallet af grupppeopstaldede ikke-lakterende søer i Europa er stigende. Årsagen er øget 

fokus på dyrevelfærd, som har resulteret i ændrede lovgivninger. Blandt besætninger med 

gruppeopstaldede søer i hele ikke-laktationsperioden er der en stor variation i reproduktionsresultater. 

Dette indikerer, at det vil være muligt at forbedre disse parametre i mange 

besætninger. På den baggrund var det overordnede mål med denne afhandling at producere 

viden, som kan forbedre beslutningsgrundlaget for driftsledere i besætninger med gruppeopstaldede 

søer. De specifikke mål var at identificere væsentlige årsager til ringe reproduktion 

hos gruppeopstaldede søer samt at definere og vurdere indikatorer velegnede til 

brug som beslutningsstøtte i kommercielle besætninger. 

Først blev et litteraturstudie af soens reproduktionsfysiologi gennemført (Appendiks 1). Det 

blev konkluderet, at energi indtag og stress kan påvirke den fysiologiske regulering af soens 

reproduktion. Da eksperimentelle studier har indikeret, at gruppeopstaldning kan føre til 

ulige energi indtag og social stress, blev hypotesen fremsat, at individuel variation i foderindtag 

og social stress kan være medvirkende årsag til ringe reproduktionsresultater hos 

gruppeopstaldede søer. For at undersøge dette nærmere blev der skrevet to review-artikler 

for at a) undersøge effekten af energiindtag (artikel I) og effekten af social stress og frygtsomhed 

(artikel II) samt b) definere indikatorer for stress og frygtsomhed velegnede til brug 

i praksis. Et studie, der inkluderede 14 besætninger med forskellige indretninger blev gennemført 

for at evaluere de definerede indikatorer (artikel III) og for at undersøge om indikatorerne 

var velegnede til at udtrykke variation i søers reproduktion under praktiske forhold 

(artikel IV). 

Artikel I 

Formålet med dette litteraturstudie var at vurdere om variationen i energiindtag i en gruppe 

af søer kan påvirke variationen i kuldstørrelse og drægtighedsprocent i praksis. På baggrund 

af en gennemgang af eksisterende litteratur med fokus på publikationer efter 1980, 

blev effekten af energiindtag i den ikke-lakterende periode på kuldstørrelse og drægtighed 

diskuteret. Baseret på litteraturstudiet og eksperimentelle studier, som havde vist, at en lavt 

rangerende sos foderindtag kan være betydeligt mindre end en højtrangerende sos (fx 50- 

80%) i gruppeopstaldning, blev det foreslået, at foderindtag hos gruppeopstaldede ikkelakterende 

søer kan variere i tilstrækkelig grad til, at både drægtighed og kuldstørrelse kan 

påvirkes negativt. 

Artikel II 

Et litteraturstudie af bl.a. 15 eksperimenter med gruppeopstaldede søer bekræftede, at stress 

og frygtsomhed kan være medvirkende årsager til ringe reproduktionsresultater hos nogle 

5


gruppeopstaldede søer. Mulige årsager til stress og frygtsomhed er sammenblanding af søer 

og høje belægningsgrader. Traditionelle metoder til at vurdere stress og frygtsomhed er 

dyre og/eller tidskrævende og derfor uegnede som komponenter i et driftsledelsesværktøj til 

at analysere og forbedre reproduktionen hos gruppeopstaldede søer. Derfor, på baggrund af 

en litteraturgennemgang, blev indikatorer, der forventedes at være velegnede til at udtrykke 

variation i søers reproduktionsresultater i praksis, defineret. 

Artikel III 

Resultater fra eksperimentelle studier indikerede, at gruppeopstaldning kan føre til individuel 

variation i foderindtag, stress og frygtsomhed. Systematisk information om variation 

mellem besætninger og indenfor besætning i forskellige gruppeopstaldnings systemer eksisterer 

imidlertid ikke. Dette skyldes formentlig, delvist en mangel på velegnede målemetoder. 

Blandt andet med det formål at evaluere indikatorer for foderindtag, stress og frygtsomhed 

samt at få indsigt i niveau og variation i disse indikatorer i besætninger med forskellige 

indretninger og driftsledelse, blev et studie gennemført, som inkluderede 14 private 

besætninger fulgt i 11 måneder. Resultaterne indikerede, at målinger af rygspæk og 

sår/rifter kombineret med adfærdsmæssige observationer var relevante indikatorer for soens 

tilstand i forhold til foderindtag, stress og frygtsomhed. For størsteparten af indikatorerne 

var variationen mellem besætninger større end variationen mellem ugehold indenfor besætning. 

Størstedelen af variationen kom dog fra variationen mellem søer. Den individuelle 

variationen i rygspæk ved faring var signifikant større i systemer med gruppefodring i fht. 

systemer med individuel fodring. Undersøgelsen indikerede, at gruppefodring kan føre til 

overfodring af de højtrangerende søer og kraftig underfodring af nogle få lavt rangerende 

søer. Tilstedeværelsen af ædebokse reducerede antallet af aggressioner den første time efter 

sammenblanding. Søer ældre end 3. læg var involveret i flest aggressioner på fravænningsdagen, 

men tre uger efter løbning havde disse søer det laveste antal sår/rifter, hvilket indikerer, 

at eventuel stress oplevet af disse søer kun har været kortvarig. I besætninger uden 

flugtmuligheder havde 1. lægssøerne flest sår/rifter tre uger efter løbning og ved faring, 

hvorimod i besætninger med flugtmuligheder havde 2. og 3. lægssøerne det højeste niveau. 

Besætninger med elektronisk sofodring og store dynamiske grupper havde det højeste niveau 

af sår/rifter. 

Artikel IV 

Eksperimentelle studier har indikeret, at gruppeopstaldning kan føre til individuel variation 

i foderindtag, social stress og frygtsomhed. Hvorvidt denne variation i praksis er af et tilstrækkeligt 

omfang til at være ansvarlig for en reduktion i reproduktionsresultater vides 

imidlertid ikke. Blandt andet derfor blev et detaljeret studie gennemført som inkluderede 14 

private besætninger med forskellige indretninger og driftsledelse, og relationen mellem 

reproduktionen og en række indikatorer for foderindtag, stress og frygtsomhed blev under- 

6


søgt. Positive korrelationer mellem rygspæktilvækst fra fravænning til tre uger efter løbning 

og sandsynligheden for drægtighed (P>0.05) og kuldstørrelse (P=0.07) blev fundet. Søer 

som åd mindre end 20% af alle observationer i forbindelse med fodring havde en signifikant 

større risiko for at løbe om i fht. søer som åd mere. Derudover, søer med mindre end 

10 mm rygspæk ved fravænning var i højere risiko for at blive udsat i fht. federe søer. Antallet 

af sår/rifter korrelerede positivt med interval fra fravænning til første løbning 

(P=0.07). Der blev ikke fundet sammenhænge mellem reproduktion og liggeadfærd, antal 

aggressioner involveret i efter sammenblanding eller frygtsomhed estimeret vha. to frygttests. 

Samlet set tyder resultaterne på, at gruppeopstaldning kan føre til tilstrækkelig individuel 

variation i foderindtag til, at reproduktionen kan påvirkes negativt. Som en følge heraf 

kan rygspækmålinger og observationer af søernes ædeadfærd muligvis være brugbare indikatorer 

af fodringsrelaterede reproduktionsproblemer hos gruppeopstaldede søer. Der blev 

ikke fundet overbevisende sammenhænge mellem indikatorerne for social 

stress/frygtsomhed og reproduktionen. Dette demonstrerer imidlertid ikke nødvendigvis, at 

der ikke er nogen sammenhæng mellem disse karakteristika og reproduktionen, men det 

viser, at de pågældende indikatorer ikke er velegnede til at afspejle gruppeopstaldede søers 

reproduktionsevne i praksis. 

Sammenfattende tyder det på, at: 

1) individuel variation i foderindtag kan være medvirkende årsag til ringe reproduktionsresultater 

hos nogle gruppeopstaldede ikke-lakterende søer 

2) rygspækmålinger og observationer af søernes ædeadfærd kan være brugbare indikatorer 

for fodringsrelaterede reproduktionsproblemer hos gruppeopstaldede søer. 

Som følge heraf, kan disse indikatorer muligvis udgøre en vigtig komponent i et 

driftsledelsesværktøj til at analysere og forbedre reproduktionen hos gruppeopstaldede 

ikke-lakterende søer. 

7

- Background and aim - 

BACKGROUND AND AIM 

For several decades, individual housing of non-lactating sows was preferred, probably because 

individual housing made it possible to control the individual sows access to important 

resources like feed and water. However, in the last decade the number of group housed nonlactating 

sows has begun to increase in Europe. This is mainly caused by elevated public 

concern of animal welfare with changed legislations as a consequence. For instance, according 

to EU legislation all sows have, from January 2013, to be loose-housed in smaller 

or larger groups from four weeks after mating until seven days before expected farrowing 

(Council Directive 2001/88/EC amending Directive 91/630/EEC Laying Down Minimum 

Standards for the Protection of Pigs). In addition, national extraordinary laws have been 

introduced in several countries. In England, for instance, all sows have to be group housed 

in the entire period from weaning to seven days before expected farrowing according to the 

national legislation (The welfare of Farmed Animals (England) (Amendment) Regulations 

2003). In Norway, the sows may only be fixed from three days before until one week after 

farrowing, and in Sweden it is only allowed to keep sows in crates for maximum one week 

if necessary during the production cyclus (Baustad & Lium, 2002). Although no laws or 

regulations so far, similar tendencies are also seen in other parts of the world (McGlone, 

2001; Trezona, 2003). 

In Denmark it is still legal to keep the sows in crates from weaning until four weeks after 

mating. Nevertheless, the Danish Bacon and Meat Council, motivated by export interests, 

has introduced an extra pay for slaughter pigs produced by sows that are group housed in 

the entire non-lactating period. This additional price has caused an increase in the number 

of sows that are group housed from weaning to shortly before farrowing in Denmark. 

However, impaired reproduction in form of reduced litter size and pregnancy rate in group 

housed compared to individual housed sows in parts of or in the entire non-lactating period 

has been observed in several Danish on-farm experiments. Sows group housed from weaning 

until two days after mating had significant fewer total born piglets compared to sows 

individually housed in the same period (Hansen, 2000). Sows group housed from weaning 

to farrowing had significant fewer total born piglets per litter than sows kept individually in 

crates the first four weeks after weaning and thereafter loose housed until farrowing 

(Fisker, 1995). Equally, in other countries a reduced farrowing rate has been seen in group 

housed compared to individual housed sows (USA: Hurtgen et al., 1980; Finland: 

Peltoniemi et al., 1999). Conversely, in other studies, no difference (conception rate and 

litter size: England & Spurr, 1969) between grouped and individually housed sows or even 

opposite effects (farrowing rate: Bates et al., 2003; Hansen, 2003) have been found. The 

divergent results are probably a result of differences in the function of the group housing 

9


systems and shows that group housing do not ‘automatically’ lead to poor reproduction 

performance. 

This is further supported by indications of a large variation in reproduction performance 

between group housing systems. In a pilot study the litter size varied from 10.6 to 13.1 born 

piglets per litter in five herds with group housed non-lactating sows (Nielsen & Calmann- 

Hinke, 1998). Data from 78 Danish herds with sows housed outdoor in the lactation period 

and in groups either inside or outside in paddocks during the non-lactating period showed 

an average farrowing rate of 78 (range 53-93) % and an average litter size of 12.1 (range 

10.6-14.1) born piglets per litter (Kirk, 2001 pers. comm.). 

The apparently large variation in farrowing rate and litter size between herds with group 

housed non-lactating sows indicates that it will be possible to improve the reproduction 

performance in some of these herds. However, to do that it is first of all necessary to identify 


sows. 

It is likely that numerous management-related factors might influence the function of group 

housing systems. Therefore, it will probably be difficult to forecast which factors may influence 

reproduction in group housed sows, merely on the background of general defined 

housing factors like stocking rate, group size, floor type etc. Furthermore, even though 

main effects of different factors can be demonstrated in experimental studies, interactions 

might lead to unexpected results in real-life conditions (Capdeville & Veissier, 2001). As a 

consequence, it seems important that managers are able to make an in situ analysis of the 

reproduction in group housed sows. To be able to perform an analysis like that, indicators 

which provide information of the function of group housing systems and suitable for use in 

practice are needed. 

On this background the overall aim of this study is to produce knowledge that managers 

can implement in their decision-making to improve the reproduction performance of group 

housed non-lactating sows. The specific aims are: 

• To identify important causes for impaired reproduction performance in group 

housed non-lactating sows. 

• To develop and evaluate indicators suitable for use in decision-making in commercial 

sow herds 

10

References 


Bates, R.O., Edwards, D.B., Korthals, R.L., 2003. Sow performance when housed either in groups with elec- 

tronic sow feeder or stalls. Livestock Production Science 79, 29-35. 

Baustad, B., Lium, B., 2002. Helse og dyrevelferd i norsk svineproduksjon sett i et internasjonalt perspektiv. 

Norsk Veterinærtidsskrift 114, 87-91. 

Capdeville, J., Veissier, I., 2001. A metod of assessing welfare in loose housed dairy cows at farm level, fo- 

cusing on animal observations. Acta Agric. Scand. , Sect. A, Animal Science Suppl. 30, 62-68. 

England, D.C., Spurr, D.T., 1969. Litter size of swine confined during gestation. Journal of Animal Science 

28, 220-223. 

Fisker, B.N., 1995. Indsættelsesstrategi for gruppefodrede drægtige søer. Meddelelse 311, Landsudvalget for 

Svin, Den rullende Afprøvning, 7pp. 

Hansen, L.U., 2000. Løbeafdeling med enkeltdyrsstier eller flokopstaldning. Meddelelse 6, Landsudvalget for 


Hansen, L.U., 2003. Løbeafdeling med enkeltdyrsstier eller flokopstaldning med permanent adgang til æde- 

/insemineringsbokse. Meddelelse 602, Landsudvalget for Svin, Danske Slagterier, 6pp. 

Hurtgen, J.P., Leman, A.D., Crabo, B. 1980. Effect of season, parity and housing factors on estrus and fertility 

in swine. Proc. Int. Pig. Vet. Soc., Copenhagen, Denmark. Pp. 20 

Kirk, A. 2001. Personal communication. Konsulent, Svinerådgivning Midt-Vest, Holstebro. 

McGlone, J.J. 2001. Alternative sow housing systems: Driven by legislation, regulation, free trade and free 

market systems (but not science). Paper presented at jan 2001 Annual meeting of the Manitoba pork 

producers, Winnipeg, Manitoba, Canada. 12pp. 

Nielsen, N.-P., Calmann-Hinke, D., 1998. Løbeafdelinger med flokopstaldede søer fodret efter ædelyst. Erfaring 

9807, Landsudvalget for Svin, Den rullende Afprøvning, 10pp. 

Peltoniemi, O.A.T., Love, R.J., Heionen, M., Tuovinen, V., Saloiemi, H., 1999. Seasonal and management 

effects on fertility of the sow: a descriptive study. Animal Reproduction Science 55, 47-61. 

Trezona, M. 2003. Welfare update: Dry sow stalls. 

http://www.agric.wa.gov.au/progserv/animal/cntnorth/porkserv/pigtales/2000/Oct2000/article08.htm. 

Department of Agriculture - Western Australia. 2pp. 

11

- Outline of this thesis - 

OUTLINE OF THIS THESIS 

A basic knowledge of how group housing varies in practice is a prerequisite for identifying 


sows. A short introduction to group housing in practice is therefore provided in How does 

group housing vary in practice. 

With the aim to identify, which processes that may go wrong and why, a brief review of the 

literature of reproduction physiology was carried out. This review is presented in Appendix 

1. 

As discussed in Appendix 1, several studies have indicated that group housing may lead to 

individual variation in energy intake and increased stress. At the same time there are several 

indications that energy intake and stress may influence the reproduction physiology of the 

sow. Therefore, two review papers were written to consider whether individual variation in 

energy intake (paper I) as well as stress and fear (paper II) could be contributing reasons for 

the lower reproduction performance in group housed compared to individually housed sows 

found in some on-farm studies. 

Based on these two review papers it was concluded that there are indications that group 

housing practice may lead to individual variation in energy intake, stress and fear which 

may influence reproduction performance negatively. However, traditional methods for assessing 

feed intake, stress and fear in sows are not suitable in large-scale on-farm studies or 

for the individual farmer, who wants to find out whether level of stress, fear and feed intake 

could be contributing reasons for reproduction problems in group housed sows. Therefore, 

a need for indicators of stress, fear and energy status suitable for use under practical conditions 

was identified. It was possible to define such indicators based upon existing knowledge 

and these indicators are presented and discussed in paper II and paper III. However, 

whether these indicators are suitable to express variation in sows susceptibility for a good 

reproduction performance under practical conditions was not known. Therefore a study in 

14 herds with different layouts and management routines was carried out. The level, the 

between-farm and within-farm variation in indicators of feed intake, fear and stress from 

the 14 herds are presented and discussed in paper III. In paper IV the relation between the 

reproduction performance (e.g. litter size and pregnancy rate) and the indicators of feed 

intake, stress and fear are presented and discussed. 

In the General discussion, the results from the four papers are discussed and put into perspective. 

Finally, a general conclusion is put forward in Conclusions. 

13

- How does group housing vary in practice? - 

HOW DOES GROUP HOUSING VARY IN PRACTICE? 

A basic knowledge of how group housing varies in practice is a prerequisite for identifying 


sows. In this chapter some of the applied housing conditions are shortly described. The description 

is based on a combination of own observations, personal communication with 

people who work with pig production in practice (e.g. advisors), literature presented in pig 

magazines and scientific journals. The description is to a large degree founded on Danish 

conditions. However, it is aimed also to include experiences from outside Denmark. 

Housing conditions may e.g. vary with 

respect to feeding procedure, timing of 

mixing of groups, group dynamics, 

group size, stocking rate and floor type. 

Feeding procedure 

In general, feeding procedure can be 

divided into two different principles: 

Group feeding and individual feeding. 

Common group feeding procedures are 

1. Floor feeding, 2. Providing liquid 

feed in long feeding troughs with or 

without individual troughs dividers and 

3. Biofix. (Svendsen et al., 1990; Brouns 

& Edwards, 1992; Olsson et al., 1993; 

Fisker, 1994). In biofix the feed is provided 

in a trough with individual 

troughs dividers in a speed that match 

the eating rate of the sows in order to 

ensure that each sow are ‘fixed’ at one 

place throughout the feeding (‘biological 

fixed’). In biofix, as in the other 

group feeding systems differential feeding 

within a group is not possible. The 

group feeding procedures mentioned are 

illustrated in Figure 1. 

Figure 1. Floor feeding, liquid feed in long 

feeding troughs and biofix (photos: L.U. Hansen 

and A.G. Kongsted). 

15


Individual feeding systems employed in practice are Electronic Sow Feeding (ESF), fitmix, 

free access feeding stalls (FAFS) and individual feeding stalls (IFS) (Brouns & Edwards, 

1992; Nielsen et al., 2000; Hansen & Petersen, 2003). In ESF, the sows are provided with 

an electronic identification mark. When the sow enters a feeding box the sow are identified 

and the ration determent to this particular sow is provided automatically. Fitmix is based on 

the same principle as ESF but the sow does not stay in a box while eating. In FAFS all sows 

are fed at the same time in individual stalls that closes when the sow enters the stall. In 

FAFS the sows have permanently access to the stalls in opposite to IFS where the sows 

only have access to the feeding stalls during feeding. In IFS, one group is feed at a time and 

when the sows from one group are finished eating the sows return to their pen and the next 

group is allowed access to the stalls. These individual feeding procedures are shown in Fig- 

ure 2. 

Figure 2. Electronic Sow Feeding (ESF), fitmix, free access feeding stalls (FAFS) and individual feeding 

stalls (IFS) (photos: L.U. Hansen). 

16


From weaning until four weeks after mating, individual feeding procedures are preferred, 

however, systems with group feeding procedures in the entire non-lactating period do also 

exist (Sørensen & Thorup, 2003; pers. comm. Hansen, 2004, own observations). 

Group dynamic/group size 

A group of non-lactating sows may either be stable or dynamic. In stable groups, once the 

group is established no new sows are moved into the group. In dynamics groups, new sows 

are constantly moved into and out of the group e.g. up till once a week (Svendsen et al., 

1990). Group sizes may vary from 2 (Deininger, 1998) to 150 (Nielsen et al., 2000) sows 

per group. In the service unit the groups are often stable with group sizes equal to or less (if 

division into smaller groups take place at weaning) than the size of the farrowing batch. 

Mixing of unfamiliar sows 

Frequently, sows are individually housed in the lactating unit why sows usually are mixed 

with unfamiliar sows when moved from the lactation unit to the service unit (Edwards, 

1992; Deininger, 1998). In some herds the service and pregnancy units are integrated. In 

these systems sows stay in the same pen from weaning to shortly before farrowing. In many 

herds, however, sows are relocated at least once more when moved from the mating to the 

pregnancy section. This may happen in from a few hours to three-four weeks (own observations) 

after insemination. 

Stocking rate 

Stocking rates from less than 2 m 2 (Mortensen & Ruby, 1990; Deininger, 1998) to more 

than 4 m 2 per sow (Svendsen et al., 1990) or even 5 m 2 per sow (Deininger, 1998) are practised. 

Often, the stocking rate in the service unit is less compared to the stocking rate in the 

pregnancy unit (pers comm., Hansen 2004) because it is believed that a high stocking rate 

in this period may influence reproduction negatively. 

Floor type 

Systems exists with large ‘open’ floor plan with deep straw bedding, however, the floor 

may also be divided into a lying/activity and a dunging area (Olsson et al., 1991). The 

dunging area may consist of slatted or concrete floor. The lying/activity area may consist of 

concrete with or without small amounts of straw provided, straw bedding or deep straw 

bedding (Deininger, 1998). It is common to use some amount of straw in the service unit 

because it is believed to minimize the risk of leg injuries caused by fighting and mounting 

during oestrus (Hansen & Kongsted, 2002). Depending upon the system in use, the amount 

of straw provided may vary from zero (own observations) to 1.000 kg per sow per year 

(Svendsen et al., 1990). The lying/activity area may be divided into smaller or larger ‘nests’ 

by means of ‘pen dividers’ as shown in picture 3. 

17


Figure 3. Electronic Sow Feeding with small (left) or large ‘nests’ (photos: L.U. Hansen). 

How are the different layout related factors combined? 

Group feeding is usually combined with small group sizes e.g. six to 20 sows per group 

(own observations) and stable groups. In opposite, ESF and fitmix are often equal to dynamic 

groups and large group sizes e.g. from 50 to 150 sows per group (Nielsen et al., 

2000). The feeding procedures FAFS and IFS are frequently combined with stable groups 

with group sizes that vary from 6 to 50 sows per group; however, it may also be combined 

with larger dynamic groups (Nielsen et al., 2000). Each of the above mentioned feeding 

procedures may be combined with each of the above mentioned floor types. 

Concluding remarks 

Group housing of non-lactating sows in practice is not a well-defined system but varies in a 

number of ways in respect to housing conditions. This variation may influence the possibilities 

of the sows to cope in the system and further affect which management options that 

can be taken in order to obtain a good reproduction performance. 

References 

Brouns, F., Edwards, S.A., 1992. Future prospects for housing of non-lactating sows. Pig News and Information 

13, 47-50. 

Deininger, E. 1998. Beeinflussung der aggressiven Auseinandersetzungen beim gruppieren von abgesetzten 

sauen durch das haltungssystem und durch andere massnahmen. Veterinär-medizinischen Fakultet 

der Universität Zürich. 120pp. 

Edwards, S.A., 1992. Scientific perspectives on loose housing systems for dry sows. Pig Veterinary Journal 

28, 40-51. 

Fisker, B.N., 1994. Løsgående gruppefodrede søer. Meddelelse 278, Landsudvalget for Svin, Den rullende 

Afprøvning., 10pp. 

18


Hansen, L.U. 2004. Personal communication. Konsulent, Afd. for stalde og produktionssystemer, Landsud- 

valget for Svin, Danske Slagterier. 

Hansen, L.U., Kongsted, A.G., 2002. Gulvudformning i løbeafdeling med æde-/insemineringsbokse til løsgå- 

ende søer. Meddelelse 559, Den rullende Afprøvning, Landsudvalget for Svin, Danske Slagterier, 

8pp. 

Hansen, L.U., Petersen, L.B., Løsgående søer. 96-97. 2003. Landsudvalget for Svin, Danske Slagterier. 

Kongres for Svineproducenter. 28-10-2003. 

Mortensen, B., Ruby, V., 1990. Transpondersystemer til drægtige søer. Meddelelse 181, Landsudvalget for 


Nielsen, N.-P., Hansen, L.U., Calmann-Hinke, D., 2000. Stalde til løsgående søer. Rapport 17, Landsudvalget 

for Svin, Danske Slagterier, 33pp. 

Olsson, A.-C., Svendsen, J., Reese, D., Andersson, M., Rantzer, D., 1993. Inhysning av dräktiga suggor i 

långsmala boxar med blötutfodring. Rapport 87, Sveriges lantbruksuniversitet, Institutionen för lantbrukets 

byggnadsteknik, Lund, 39pp. 

Svendsen, J., Andersson, M., Olsson, A.-C., Rantzer, D., Lundqvist, P., 1990. Grupphållning av drägtiga 

suggor i isolerade och oisolerade stallar. En beskrivning av resultaten från enkätunder - sökningar, 

gårdsbesök och grupperingsförsök. Rapport 66, Institutionen för lantbrukets byggnadsteknik, Sveriges 

Lantbruksuniversitet, 202pp. 

Sørensen, G., Thorup, F., 2003. Energitildeling i implantationsperioden. Meddelelse 618, Landsudvalget for 

Svin, Danske Slagterier, 7pp. 

19

- Paper I - 

Effect of energy intake on pregnancy rate and litter size with particular 

reference to group housed non-lactating sows - a review 

A.G. Kongsted 

Department of Agroecology, Danish Institute of Agricultural Sciences, P.O. Box 50, DK- 

8830 Tjele 

Submitted to Livestock Production Science 

21 

I

- Paper I - 

Abstract 

The number of group housed non-lactating sows is increasing rapidly in Europe as a consequence 

of changed legislation initiated by elevated public concern of animal welfare. Lower 

litter size and pregnancy rate in group compared to individual housed non-lactating sows 

have been observed in several on-farm experiments. The aim of this review is to consider 

whether the variation in energy intake in a group of non-lactating sows can influence variation 

in litter size and pregnancy rate in practice. Through a review of existing literature with 

main emphasis on publications after 1980, the effect of energy supply before mating and in 

pregnancy on pregnancy rate and litter size is discussed. The results indicate that low compared 

to high energy intake before mating may impair litter size in gilts and in sows that 

experienced severe weight loss during lactation. Furthermore, it seems that moderate compared 

to low energy intake the first three days after mating may reduce litter size in the gilt 

but not in the sows. However, very low energy intake the first four weeks in pregnancy may 

impair litter size in gilts and sows and also pregnancy rate in gilts. Whether the last mentioned 

is also the case for sows is not possible to conclude. However, it seems that low energy 

intake for several successive parities can increase the risk of being culled as a consequence 

of not being pregnant. Based upon studies indicating that low ranking sows may 

consume considerably less than high ranking sows (e.g. 50-80%) in group housed systems, 

it is suggested that variation in feed intake in a group of restricted fed pregnant female pigs 

may be large enough to influence pregnancy rate and litter size. 

Keywords: Sow, Gilt, Group housing, Energy intake, Reproduction, Litter size, Pregnancy 

rate 

22

- Paper I - 

1. Introduction 


of changed legislation initiated by elevated public concern of animal welfare. According 

to EU legislation from January 2013, all sows have to be loose-housed in smaller or 

larger groups from four weeks after mating until seven days before expected farrowing 

(Council Directive 2001/88/EC amending Directive 91/630/EEC Laying Down Minimum 

Standards for the Protection of Pigs). In United Kingdom, all sows have to be group housed 

in the entire period from weaning to seven days before expected farrowing according to the 

national legislation (Mortensen, 1997). In Norway, the sows may only be fixed from three 

days before until one week after farrowing and in Sweden, it is only allowed to keep sows 

in crates for maximal one week if necessary during the production cyclus (Baustad & Lium, 

2002). Similar tendencies are seen in other parts of the world (Trezona, 2003). 

Impaired reproduction in form of reduced litter size and pregnancy rate in group housed 

sows compared to individual housed sows in parts of or in the entire non-lactating period 

has been observed in several on-farm studies. The impairment has been in the range of 0.3 

(Hansen, 2000) to 0.6 (Fisker, 1995) less born piglets per litter, 0.9 %-point lower farrowing 

rate (Hurtgen et al., 1980) and 3.4 %-point higher repeat breeding rate in autumn 

(Peltoniemi et al., 1999). However, in other studies, no difference (Gjein & Larssen, 1995; 

Hansen, 2003) or even opposite effects have been found (Bates et al., 2003; Hansen, 2003). 

The divergent results are probably a result of differences in the function of the group housing 

systems. 

Systems with group housed non-lactating sows can vary in a number of ways, e.g. in group 

size, group dynamics, floor type and feeding system. A commonly used feeding procedure 

is group feeding, providing the feed on the floor or in long feeding trough. These feeding 

procedures are economical attractive because of the low investments costs, however, the 

disadvantage is that individual rationing is not possible. A more expensive alternative to 

group feeding is individual feeding. Examples of popular individual feeding procedures are 

the Electronic Sow Feeding (ESF) system, where sows are fed automatically in a crate, one 

at a time (Brouns & Edwards, 1992), and one feeding stall per sow, where all sows are fed 

at the same time in individual crates that closes during eating (Nielsen et al., 1997). 

In systems with group feeding, the individual sow is not protected during feeding from displacements 

by other sows and studies have indicated lower feed intake in low ranking sows 

compared to high ranking sows in form of lower weight gain (Brouns & Edwards, 1994; 

Ruis et al., 2002), less increase in chest girth (Olsson & Svendsen, 1997), less time spent at 

the central area of a pile of feed provided on the floor (Csermely & Wood-Gush, 1990) and 

23

- Paper I - 

less time spent at the trough (Andersen et al., 1999). This indicate that group housed sys- 

tems without individual feeding can lead to individual variation in feed intake between 

sows. However, even in group housed systems with individual feeding, such as ESF, lower 

feed intake in the low and middle ranking sows has been indicated (Mendl et al., 1992). 

The reason for this might be that the low and middle ranking sows do not always eat the 

ration allocated because of intimidation from sows waiting outside the feeder (Mendl et al., 

1992). Furthermore, experiences from practice show that high ranking sows visit the feed 

station several times to lick feed left over, this may make it more difficult for the low ranking 

sows to gain access to the feed station (Olsson & Svendsen, 1997). 

Sows are often fed ad libitum or close to ad libitum before mating (flushing) in commercial 

practice. In Denmark, for instance, recommendation for energy supply, in the period from 

weaning to mating, is 51-77 MJ ME day -1 (The National Committee for Pig Production, 

2003a). When feed is provided ad libitum during pregnancy, the low ranking sows have 

been found to have comparable feed intake with higher ranking individuals (Brouns & Edwards, 

1994). However, in herds with group housed non-lactating sows, the sows are usual 

mixed with unfamiliar sows after weaning and when unfamiliar sows are mixed, fighting 

occur until a hierarchy is established (Arey & Edwards, 1998). Mixing with unfamiliar 

sows seems to be a stressful condition with increased level of plasma cortisol as a consequence 

(Barnett et al., 1981; Dalin et al., 1993; Tsuma et al., 1996) especially for the sows 

receiving most aggressions (Mendl et al., 1992). The effect of stress upon appetite in pigs 

has not yet been studied as far as we know. However, there are indications that stress may 

reduce appetite in rats (Rodríguez Echanía et al., 1988; Ottenweller et al., 1989). It is therefore 

likely that sows involved in many fights will have reduced appetite and therefore reduced 

feed intake even though the feed is provided ad libitum. 

In commercial practice, pregnant sows are usual fed amounts far below their capacity for 

feed intake (Brouns et al., 1991). Therefore, pregnant sows are motivated to eat throughout 

the day (Jensen et al., 2000) and competition for food is a major cause of aggressions in 

group feeding systems (Olsson et al., 1993). As mentioned above, there are indications that 

this may lead to an uneven energy intake in low and high ranking sows during pregnancy. 

For the above-mentioned reasons, it is believed that individual variation in energy supply is 

likely to occur in group housing systems both before mating and in pregnancy. It is generally 

agreed that energy intake can influence reproduction related processes in the female pig 

(Einarsson & Rojkittikhun, 1993; Cosgrove & Foxcroft, 1996; Foxcroft, 1997; Prunier & 

Quesnel, 2000ab). Therefore, one reason for the lower litter size and pregnancy rate in 

group housed sows compared to individual housed sows seen in some on-farm studies 

could be individual differences in energy intake between sows. 

24

- Paper I - 

Therefore, the aim of this review is to consider whether the variation in feed intake in a 

group of non-lactating female pigs can influence the variation in litter size and pregnancy 

rate in practice. 

Emphasis will be upon studies made in the eighties and forth. Several studies in the sixties 

and seventies have examined the effect of energy intake on pregnancy rate and litter size. 

However, intense genetic selection has changed the genotype of breeding sows why some 

of the early work may no longer be relevant to commercial sow herds (Ashworth & Antipatis, 

1999). 

Pope (1994) and Foxcroft (1997) point out that it is important to consider the effect of nutrition 

in the different reproductive stages of the sows separately because the effect in the 

different phases can vary. Furthermore, from a practical point of view, it is important to 

know when the sow’s reproduction is most susceptible to a low or a high energy intake because 

only then it is possible to adjust the feeding system in the different stages. This could 

be of outmost economical importance for the individual farmer because individual feeding 

procedures, like for instance one feeding stall per sow, are much more expensive than 

group feeding procedures, like floor feeding. Therefore, in this review, the effect of energy 

intake will, whenever possible, be divided into 1) Effect of energy intake before mating (in 

the oestrus cycle or after weaning) 2) Effect of energy intake in the early pregnancy (also 

called the embryonic phase i.e. the first 35 days after fertilization) and 3) Effect of energy 

intake in the mid and late pregnancy. 

2. Effect of energy intake before mating 

In Table 1, the results from the 12 experiments presented in this chapter are summarized. In 

these experiments, the effect of energy intake before mating on ovulation rate; number of 

embryos and/or pregnancy rate has been studied. 

25

Refer 

ence 

Table 1. Effect of energy intake before mating upon ovulation rate, number of embryos and pregnancy rate 

Feed supply, MJ ME day -1 N Parity Daily gain, 

1 H: 2.6 kg 1) 

L: 0 

2 HHHH: 2.3, 2.3, 2.3, 2.3 kg 1) 

LLHH: 0, 0, 2.3, 2.3 kg 

LLLH: 0, 0, 0, 2.3 kg 

LLLL: 0, 0, 0, 0 

3 H: 34.3 MJ NE4) L: 21.4 MJ NE 

4 H: 44.8 

L: 0 

5 H: 3.60 kg 1) 

L: 1.8 kg 

5 L: 1.8 kg 1) 

H: 0, 2.7, 1.8 kg 

6 H: ad lib 

L: 19.3 

7 H: 41.7 

L: 24.2 

36 2) 

36 2) 

107 

in all 

37 

32 

63 

65 

74 

75 

98 

98 

40 

40 

18 

18 

g 

0 416 

1 

-636 

(After 42 days) 

1 450a 

-280b 

- 

Ovulation rate Embryo survival, 

11.6a 

9.5b 

14.8a 

13.0 

13.3 

12.6b 

(30 days La.) 

15.2 

14.8 

% 

89.7 

88.7 

80.5 

80.7 

77.7 

77.4 

(30 days La.) 

Number of embryos Pregnancy rate Treatment period 

10.4 

8.4 

11.9/11.8a 

10.3/8.0b 

10.7/10.5 

9.7/11.3 

(Embryos 

day 25/litter size) 3) 

Different - - - 12.0x 

11.1y 

(Litter size) 

Different - - - 10.6 

10.4 

(Litter size) 

Different - - - 10.5 

10.4 

(Litter size) 

1 716 

294 

14.8a 

13.0b 

0 - 17.6a 

14.0b 

100 

61 

(Remained pregnant) 

10 days before ma. until 14, 18, 22, 26, 30 or 34 

days a. ma. 

- Day 1, 2, 3 and 4 a.w. 

- - - w.-ma. (9.1,8.2 days) 

0.68 

0,74 

74 

80 

(60 days after ma.) 

10.0 

9.5 

(Litter size) 

12.9x 

10.8y 

86 

90 

77 

85 

(Farrowing rate) 

83 

80 


On the day of w. 

w.-6 days a.w. 

(Mated in average on day 4.5 a.w.) 

w.-f. 

w.-2 days a.w., 2 days a.w.-ma., ma.-f. 

- w.-ma. (17.1,16.7 days) 

73 

73 

6 days before oestrus until 24 hour after oestrus 

To be continued on next page

Refer 

ence 

Table 1. Effect of energy intake before mating upon ovulation rate, number of embryos and pregnancy rate (continued) 

8 H: 46.1 

Feed supply, MJ ME day -1 N Parity Daily gain, 

L: 22.6 

9 HH: ad lib, ad lib 

LH: 25, 35 

LL: 25, 25 

10 HH: 74.4,74.4 

HL: 74.4,37.2 

LH: 37.2,74.4 

LL: 37.2,37.2 

8 

8 

14 

13 

14 

23 

22 

22 

22 

g 

0 173a 

650b 

Ovulation 

rate 

16.0a 

9.4b 

0 - 12.7a 

12.1a 

10.7b 

2 - 16.6 

16.2 

17.7 

16.7 

5) 

Embryo survival, 

% 


- - - Day 8 of second oestrus cycle until the end of 

oestrus cycle 

- - - From 45.3 kg BW to puberty and from puberty to 

second oestrus 

77.7ab 

85.0a 

70.4bc 

64.0c 

- 86.9a 

82.0a 

69.0b 

62.0b 

(Pregnancy rate) 

La., w.-ma. (6.6,6.7 days) 

11 HH: 44.0, 45.3 

22 0 714 

17.1 

83-6a 

14.3 

- Day 1-7 and day 8-15 in oestrus cycle 

HL: 44.0, 34.0 

19 

642 

18.5 

68.3b 

12.8 

LH: 32.7, 45.3 

21 

595 

17.7 

81.7a 

14.7 

(One cyclus) 

Note: In some references the level of energy is only reported in DE, in those cases ME is calculated as 0.96*DE (Theil et al. (2002)) 

Ma.: Mating, F.: Farrowing, W.: Weaning, La.: Lactation, A.: After 

A, b, c: Values with different superscripts are significant different (P≤0.05). x, y, z: Values with different superscripts tended to be different (P

- Paper I - 

Gilts 

When it comes to gilts, the effect of flushing is confirmed in several studies (Cox et al., 

1987; Flowers et al., 1989; Beltranena et al., 1991). The experiments mentioned, have all 

been investigating the effect of high (41.7 MJ ME day -1 -ad libitum) contra low (22.6-25 MJ 

ME day -1 ) energy intake. A moderate restriction in energy intake (34.0 MJ ME day -1 ) during 

day 8-15, but not during day 1-7, in oestrus cycle, seems to impair embryo survival, 

however, the number of embryos at day 28 in pregnancy were not affected significantly 

(Almeida et al., 2000). 

The effect of more restricted feeding of gilts before mating has, as far as we know, not been 

studied in the recent years but Anderson (1975), who investigated the effect of total starvation 

of gilts in ten days before mating, found that the ovulation rate was reduced compared 

to control animals given a full diet (2.7 kg). The question is, however, whether this lower 

ovulation rate will result in lower litter size because a positive correlation between the ovulation 

rate and the embryo mortality seems to exist (Toplis et al., 1983). In the study by Cox 

et al. (1987), the number of fetuses 60 days after mating tended to be decreased in the sows 

fed the low energy intake (P

- Paper I - 

Therefore, low energy supply compared to flushing does not seem to have any effect when 

looking isolated at the period from weaning to mating. Whether it has an effect in sows that 

experience severe weight loss during lactation is difficult to say because the results are inconsistent. 

King & Williams (1984) did not find any significant interactions between feed 

intake in lactation (25 MJ ME day -1 or ad libitum) and feed intake from weaning to mating 

(19.3 or 50.1 MJ ME day -1 ) on litter size in first litter sows even though the restricted fed 

sows had a weight loss of 37 kg during lactation. However, Baidoo et al. (1992) found a 

significant interaction between feed intake during lactation and feed intake after weaning in 

second parity sows because low feed supply after weaning reduced embryo survival only in 

sows fed restricted during lactation. 

Nielsen et al. (1981), reported that fasting compared to 44.8 MJ ME on the day of weaning 

resulted in a non-significant (P=0.08) smaller litter size. In contrast, Tribble & Orr (1982) 

were not able to find any effect of fasting two days after weaning. Perhaps the lacking effect 

in Tribble & Orr (1982) is due to a shorter lactation length (18-38 days compared to 

28-56 days in Nielsen et al. (1981) since Allrich et al. (1979) only found an effect of starvation 

after mating on litter size in sows lactating for 30 days and not in sows lactating for 21 

days. Weight loss during lactation is not reported in the mentioned studies but it is however 

likely that weight loss is higher, the longer lactation length, why these results confirm that 

the effect of low feed intake after mating depends upon the condition of the sow at weaning. 

All in all, there seems to be no evidence of an effect of low energy intake (19.3-37.2 MJ 

ME day -1 ) compared to flushing (ad lib or close to ad lib) from weaning to mating on ovulation 

rate in sows. However, it is possible that low feed intake (37.2 MJ ME day -1 ) has a 

negative effect on litter size in sows that experienced severe weight loss (e.g. 39 kg) during 

lactation. Pregnancy rate does not seem to be influenced by energy intake before mating. 

3. Effect of energy intake in early pregnancy 

In Table 2, the results from the 13 experiments presented in this chapter are summarized. In 

these experiments, the effect of energy intake in early pregnancy on number of embryos 

and/or pregnancy rate has been studied. 

29

Table 2. Effect of energy intake in early pregnancy upon number of embryos and pregnancy rate 

Refe- 

rence 

1 H: 2.7 kg 1) 

L: 0 

2 HH: 29.4, 29.4 

HL: 29.4, 17.6 

LH: 17.6, 29.4 

LL: 17.6, 17.6 

3 L: 25,0 

H: 50,1 

4 H: 23.09 

M: 16.84 

L: 10.58 

5 HH: 72.2, 43.3 

HL: 72.2, 21.6 

LH: 36.1, 43.3 

LL: 36.1, 21.6 

Level in treatments, 

MJ ME day -1 

6 L: 15.7 (Slaughtered a. 30 days) 

H: 31.4 (Slaughtered a. 30 days) 

L: 15.7 (Slaughtered a. 60 days) 

H: 31.4 (Slaughtered a. 60 days) 

L: 15.7 (Slaughtered a. Fa.) 

H: 31.4 (Slaughtered a. Fa.) 

N Parity Daily gain, g Ovulation rate Embryo survival, 

36 

48 

31 

29 

31 

28 

16 

18 

24 

23 

22 

28 

29 

25 

22 

24 

25 

25 

27 

84 

79 

0 416 

-636 

(After 44 days) 

0 0,42a 

0,15b 

0,36a 

0,12b 

6-7 313a 

757b 

4.9 2) -70 

-34 

-86 

2 280 

164 

120 

72 

0 -30 

710 

30 

750 

10 

720 

11.6a 

9.5b 

12,5 

12,5 

13,2 

12,0 

23.38 

23.89 

% 

89.7 

88.7 

75,8 

76,9 

85,4 

86,7 

LL+LH: 86.2a 

HH+HL: 75.2b 

17.58 

16.76 


10.4 

8.4 

9,5 

9,6 

11,2 

10,5 

LL+LH: 11.0a 

HH+HL: 9.5b 

0.75 

0.72 

- - 11.33 

10.57 

10.73 

(Litter size) 

- 80.6a 

84.6ac 

75.8ad 

67.4b 

13,6 

13,4 

13,4 

12,7 

82,5 

85,1 

82,4 

81,8 

13.8a 

14.5ac 

13.1ad 

11.5b 

11,2 

11,6 

11,2 

10,3 

10,5 

10,4 

100 

61 

(Remained pregnant) 

87.1a 

86.2a 

87.1a 

64.3b 

10 days before ma. Until 14, 

18, 22, 26, 30 or 34 days 

a.ma. 

1-10 and 11 – 30/35 days 

a.ma. 

- 3-30 days a.ma. 

75 

72 

69 


82 

97 

76 

77 

1-10 days a.ma. 

La., 0-25 days a.ma. 

- 0-10 days a.ma. 


Table 2. Effect of energy intake in early pregnancy upon number of embryos and pregnancy rate (continued) 

Refe- 

rence 

Level in treatments, 

MJ ME day -1 

7 Ll: 23.6 (P: 7.8 g /BW kg 0.75 ) 

Lh: 23.6 (P: 13.0 g/BW kg 0.75 ) 

Hl: 38.4 (P: 7.8 g/BW kg 0.75 ) 

Hh: 38.4 (P: 13.0 g/BW kg 0.75 ) 3) 

8 L: 21.4 

H: 34.6 

9 L: 22.6 

H: 33.9 

9 L: 20.6 

H: 33.9 

10 L: 23.0 

M: 29.4 

H: 38.4 

11 L1: 22.8 

L2: 22.8 

H: 31.3 

N Parity Daily gain, g Ovulation rate Embryo survival, 


12 0 216a 

13.7 

% 

- 12.2 

- 3-15 days a.ma. 

12 

200a 

15.1 

12.8 

12 

758b 

14.2 

12.4 

12 

750b 

14.8 

11.6 

91 0 - - 76.4 

78.6 

- - 0 - 9/10/11 days a.ma. 

36 

36 

34 

34 

614 

634 

631 

(Litter) 

24 

22 

21 

0 400a 

700b 

0 310a 

560b 

Gilts & 

sows 

0 657 

760 

830 

13.6 

13.5 

13.9 4) 

13.9 

71.,3a 

83.7b 

79.1 

78.4 

9.6a 

11.2b 

11.0 

10.9 

- - - 11.6 

11.7 

11.9 

(Litter size) 

14.50 

14.95 

14.95 

85.93a 

77.35ab 

66.96b 

12 L: 13 

369 Sows -321 

- - 14.9a 

M: 31 

378 

285 

15.1a 

H: 49 

364 

1000 

15.4b 

(Litter size) 

Note: In some references the level of energy is only reported as DE, in those cases ME is calculated as 0.96*DE (Theil et al. (2002)) 

Ma: Mating, F: Farrowing, W: Weaning, La: Lactation, A: After 

12.25 

11.04 

9.80 

- 3-30 days a.ma. 

- 3-24 days a.ma. 

85.9 

88.4 

88.4 



- L1: 1-15 days a.ma. 

L2: 3-15 days a.ma. 

H: 1-15 days a.ma. 

86.4 

88.5 

86.9 



a, b, c: Values with different superscripts are significant different (P≤0.05). x,y, z: Values with different superscripts tended to be different (P

- Paper I - 

Gilts 

Moderate energy supply (29.4 MJ ME day -1 ) compared to low energy supply (17.6 MJ ME 

day -1 ) both from mating until 30/35 days after mating and from mating until ten days after 

mating increased the embryonic mortality and reduced the number of embryos in gilts 

(Dyck & Strain, 1983). Some authors argue that a lower embryo survival in gilts fed moderate 

energy intake could be due to the ovulation rate being increased and hence, the embryo 

mortality as a result of the moderate energy intake immediately after mating (Toplis et 

al., 1983). However, in the present study, the ovulation rate did not differ between the treatments. 

Therefore, this could probably not be the explanation. Jindal et al. (1996) also found 

that moderate energy supply in gilts the first 15 days after mating resulted in a significant 

lower embryo survival and a non-significant lower number of viable embryos at day 25-30 

compared to low energy supply. These authors also found an inverse relationship between 

plane of nutrition and circulating progesterone concentrations. Furthermore they observed 

that the group of gilts with the greatest average plasma progesterone concentration had the 

greatest embryonal survival. Similarly, Pharazyn et al. (1991) observed that overall plasma 

progesterone concentrations on day three after oestrus were positively related to embryo 

survival. Perhaps increases in energy intake leading to rapid gains will result in reduced 

embryo survival because of an increase in metabolic clearance of progesterone as a 

consequence of increased hepatic blood flow (Einarsson & Rojkittikhun, 1993) 

Reduced levels of energy from day three to day 15 of gestation did not have an effect on the 

number of embryos in the uterus at day 28 (Pharazyn et al., 1991). Similarly, Jindal et al. 

(1996) found that low energy supply from day three after mating until day 15 does not effect 

embryo survival. Therefore, these authors suggest that a reduction in feed intake has a 

positive effect but only if it occurs in the first days after onset of oestrus. This is in agreement 

with other studies beginning treatment three days after mating and finding no effect 

(Liao & Veum, 1994) or even a negative effect (Liao & Veum, 1994) of low compared to 

moderate energy supply. 

In the light of the above-mentioned results, it seems that a low feed intake (17.6/22.8 MJ 

ME day -1 ) the first days after mating has a positive effect on reproduction performance 

compared to moderate feed intake (29.4/31.3 MJ ME day -1 ). However, in other studies with 

treatment beginning immediately after mating, no positive effect of low energy supply 

(15.7/21.4 MJ ME day -1 ) was found compared to moderate energy supply (31.4/34.6 MJ 

ME day -1 ) on embryo survival (Dyck, 1991; Cassar & King, 1992) or number of foetuses 

(Dyck, 1991). So, the results are inconsistent. Foxcroft (1997) argues that the inconsistency 

in much of the literature regarding effect of energy intake on embryo survival could be due 

to differences in number of animals used and level of embryo survival in the control group. 

32

- Paper I - 

However, this does not seem to be a possible explanation for the conflicting results in the 

mentioned studies given in Table 2. 

Anderson (1975) studied the effect of total starvation from ten days before mating to respectively 

14, 18, 22, 26, 30 and 34 days after mating and found no differences in embryo 

survival rate in the sows that remained pregnant compared to control animals given a full 

diet (2.7 kg). The number of embryos was lower in the starved sows but this was because of 

a lower ovulation rate and therefore probably founded before mating. 

The effect of energy intake in early pregnancy on pregnancy rate has not been subject for 

much research. Dyck & Strain (1983) found that the group with low energy supply (17.6 

MJ ME day -1 ) in the entire period from mating to 30/35 days after mating had lower pregnancy 

rate (64.3%) than the other groups (86.2-87.1%). This was not the case for sows with 

low energy supply only in the first ten days of pregnancy. The conception failure occurred 

after day ten and before day 30 and the authors therefore hypothesized that the conception 

failure was due to failure of either early embryonic growth or implantation. 

It has not been possible to find more recent references about the effect of energy intake in 

early pregnancy on conception rate. However, Anderson (1975) investigated the effect of 

total inanition in gilts from ten days before mating until 14, 18, 22, 26, 30 and 34 days respectively 

after mating. They found that 22 of 36 gilts (61 %) remained pregnant. Of these 

gilts, six out of six (100 %) remained pregnant after day 14 after mating whereas 13 out of 

18 (72 %) remained pregnant when inanition continued to day 18, 22 and 26 after mating 

and inanition longer than that resulted in a pregnancy rate of 25 % (three of 12 gilts). 

In summary, there are indications that moderate (31.3 MJ ME day -1 ) compared to low 

(17.6-22.8 MJ ME day -1 ) energy supply in the first three days after mating can influence 

embryo survival negatively in gilts. However, the results are conflicting. The effect of very 

low feed intake in early pregnancy in gilts has almost not been studied, but one study did 

not find a negative effect of total starvation compared to moderate feed intake in early 

pregnancy (34 days) on embryo survival rate in the sows that remained pregnant. Regarding 

pregnancy rate, it seems that low energy intake (17.6 MJ ME day -1 or less) compared to 

moderate energy supply (29.4 MJ ME day -1 , 2.7 kg) the first 30/35 days in pregnancy may 

have a negative effect. 

Sows 

High energy supply (50.1, 38.4, 48.6 MJ ME day -1 ) when treatment beginning three days 

after mating (Toplis et al., 1983) or immediately after mating (Sørensen, 1994) does not 

33

- Paper I - 

seem to impair the number of embryos (Toplis et al., 1983), litter size or farrowing rate 

(Sørensen, 1994; Sørensen & Thorup, 2003) in sows. 

When looking isolated at energy intake in pregnancy, there is apparently no effect of low 

energy intake (21.6, 23.0 MJ ME day -1 ) the first four weeks on the number of embryos 

(Kirkwood et al., 1990), litter size or farrowing rate (Sørensen, 1994). However, this is perhaps 

only the case when sows are in a good condition at weaning because Kirkwood et al. 

(1990) found a lower number of embryos in sows restricted fed during lactation (36.1 MJ 

ME day -1 ) and the first 25 days of pregnancy (21.6 MJ ME day -1 ) compared to sows fed 

close to ad libitum in lactation and restricted fed the first 25 days of pregnancy. 

Very low feed intake (10.6 MJ ME day -1 ) day one to day ten in pregnancy did not affect the 

number of piglets born (total or alive) or the farrowing rate (Dyck & Cole, 1986). However, 

as found in the study by Dyck & Strain (1983), it seems that low feed intake only has an 

effect after day ten of pregnancy, so perhaps a longer period of very low energy intake 

would have influenced the farrowing rate in sows. This is confirmed in a study by Sørensen 

& Thorup (2003) who found that very low energy intake (13 compared to 49 MJ ME day -1 ) 

the first 28 days in pregnancy, reduced the litter size significantly. 

All in all, there seems to be no evidence that high (≥38.4 MJ ME day -1 ) energy intake in the 

first 28 days of pregnancy impair the litter size in sows. It seems that low energy intake 

(21.6 MJ ME day -1 ) the first four weeks of pregnancy may impair the litter size only in 

sows fed very restricted during lactation. Very low energy intake (10.6 MJ ME day -1 ) the 

first ten days in pregnancy does apparently not impair the litter size or the pregnancy rate 

but very low energy intake (13 MJ ME day -1 ) for a longer period (28 days) may impair the 

litter size. 

4. Effect of energy intake in mid-/late pregnancy and in several successive pregnancies 

In Table 3, the results from the seven studies presented in this chapter are summarized. In 

these experiments, the effect of energy intake in mid- and late pregnancy and in several 

successive pregnancies on number of embryos; litter size and/or culling rate has been studied. 

34

Table 3. Effect of energy intake in mid- and late pregnancy and in several successive pregnancies upon number of embryos and pregnancy rate 

Refe- 

rence 

1 H: 30.5 

Level in treatments, MJ ME day -1 N Daily gain, g Number of embryos Pregnancy rate Treatment period 

L1: 24.4 

ML2: 24.4→ 18.3 1) 

L2: 18.3 

2 H: 37.2 

M: 26.7 

L: 16.2 

3 M1: 2.3 kg 3) 

M2: 2.0 kg 

L: 1.7 kg 

4 M: 28.8 

L: 23.8 

4 H: 35.2 

M: 31.9 

L: 28.8 

23 

23 

22 

23 

9 

9 

8 

20 

20 

20 

160 

164 

163 

153 

150 

- 8.3 2) 

9.0 

8.2 

8.8 

(Litter size) 

41.4a 

27.6b 

2.3c 

11.5 

11.1 

10.7 

(Litter size) 

- H: 10.8 

M: 10.4 

L: 11.1 

(Litter size) 

11.9-47.9 

2.4-39.8 

(Pregnancy) 

59.3-40.7 

53.7-32.5 

47.6-16.3 

(Pregnancy) 

9.5a 

10.0b 

(Litter size) 

10.3 

10.7 

10.6 

(Litter size) 

- 2 days a.w.-f 

Four successive gestations 

- Day 43-114 in pregnancy 

- Five successive gestations 

- Five successive gestations 

- Six successive gestations 


Table 3. Effect of energy intake in mid- and late pregnancy and in several successive pregnancies upon number of embryos and pregnancy rate (continued) 

Refe- 

rence 

5 H: 34.6 

Level in treatments, MJ ME day -1 N Daily gain, g Number of embryos Pregnancy rate Treatment period 

M: 28.1 

L: 21.4 

61 

63 

63 

- 11.2 4) 

10.8 

11.6 

More culled sows in L (main reasons: not 

pregnant and aborted) 

1 day a.w.-109 days a.ma. 

Four successive gestations 

6 H: 38.5 

48 

58-65a 

13.6 

- Two successive gestations 

L: 22.2 

48 

21-25b 

12.3 

(Pregnancy) 

(First parity) 

Note: In some references the level of energy is only reported as DE, in those cases ME is calculated as 0.96*DE (Theil et al. (2002)) 

Ma.: Mating, F: Farrowing, W: Weaning, La: Lactation, A: After 

a, b, c: Values with different superscripts are significant different (P≤0.05). x,y, z: Values with different superscripts tended to be different (P

- Paper I - 

Feeding sows 16, 27 or 37 MJ ME day -1 from day 43 to day 114 in pregnancy did not influ- 

ence the litter size (Merk & Kirchgessner, 1984) and in accordance with this, Einarsson & 

Rojkittikhun (1993) suggest that feed level of pregnant sows after the first four weeks has 

little effect on litter size. 

Litter size seems to be unaffected even by low energy supply (e.g. 18.3 MJ ME) during 

pregnancy for several parities (Walker, 1983; Whittemore et al., 1984), though, the results 

should be treated with caution due to a relative low number of sows per treatment group (23 

followed in four gestations, 20 followed in five gestations). However, also in larger scale 

studies, no convincing effect of low energy supply for two (Spoolder et al., 1996), four 

(Young et al., 1990) or five (Gatel et al., 1987) parities on litter size has been observed. In 

some trials, a higher culling rate was seen among the low fed sows (Walker, 1983; 

Whittemore et al., 1984; Young et al., 1990) and when the culling reason was reported, 

main reasons were reproductive problems like for instance not pregnant and abortions 

(Young et al., 1990). In contrast, Gatel et al. (1987) found a slightly higher culling rate for 

less restricted fed sows (35.2 MJ ME day -1 ) but this was primarily due to anoestrus after 

weaning and leg problems. Locomotion problems are a well-known consequence of high 

feed intake during pregnancy (Dourmad et al., 1994). In practice, this could imply consequences 

for litter size and pregnancy rate because a higher culling rate will lead to a higher 

proportion of first-litter sows in the herd and since younger sows are less prolific than older 

sows, this would lead to a reduction in average reproduction performance. 

There are several reports of a negative relationship between feed intake during pregnancy 

and feed intake in lactation (e.g.Yang et al., 1989; Young et al., 1990; Xue et al., 1997) and 

a low feed intake in lactation may reduce ovulation rate and embryo survival (Zak et al., 

1997; Han et al., 2000) and perhaps even conception rate (Hughes et al., 1984) in the next 

cyclus. The question is, however, how high feed intake in pregnancy should be before feed 

intake in lactation is reduced so much that litter size and conception rate is impaired. In the 

above-mentioned long-term trials, the level of feed intake in pregnancy was in the range 

from low level (18.3-22.2 MJ ME per day) to moderate level (30.5-38.5 MJ ME per day) 

and in these trials, apparently no negative effect of the moderate level of feed intake on 

litter size was observed in the subsequent cyclus. However, whether higher feed intake during 

pregnancy can influence litter size negatively by reducing feed intake in lactation, is not 

possible to conclude based on these studies. 

In summary, when looking isolated upon one cyclus, energy supply after the first four 

weeks of pregnancy is believed to have little effect on reproduction performance. Regarding 

effect of energy intake in several successive pregnancies on reproduction, low energy 

intake (21.4 MJ ME day -1 ) for up till five parities does not seem to reduce litter size. However, 

low energy intake in several gestations may increase the risk of being culled due to 

37

- Paper I - 

pregnancy failure. There is a negative correlation between feed intake during gestation and 

feed intake during lactation, for which reason very high feed intake during gestation may 

lead to low energy intake in lactation and thereby perhaps a lower litter size and pregnancy 

rate in the following cyclus. However, how high the feed intake in pregnancy shall be be- 

fore reproduction in the next cyclus is impaired, is not possible to say. 

5. Discussion 

The results reviewed do not provide a clear picture of the relation between energy supply 

and reproduction in female pigs because the results are often inconsistent. It is therefore 

difficult to draw unambiguous conclusions, however, some lines can be drawn. 

First of all, it seems that the reproduction performance of gilts in general is more influenced 

by energy supply than the reproduction performance of the sow. There are indications that 

ovulation rate and thereby litter size can be impaired in gilts if they are fed restricted (≤25 

MJ ME day -1 ) before mating. When it comes to the sow, the picture is much less clear. 

Energy intake from weaning to mating seems to have little influence on litter size although 

moderate energy intake (37 compared to 74 MJ ME day -1 ) did impair litter size in sows that 

experienced severe weight loss (39 kg) during lactation in one study (Baidoo et al., 1992). 

There are indications that litter size in gilts can be reduced if they are fed moderate (≥31 MJ 

ME day -1 ) compared to low (18-23 MJ ME day -1 ) level of energy the first three days after 

mating. Whether this is also the case for the sow has not been confirmed. The number of 

born piglets per litter seems to be highly resistant to even starvation in early pregnancy in 

some female pigs, however, there are indications that very low energy intake (≤13 MJ ME 

day -1 ) the first four weeks in pregnancy may impair litter size. Less restricted energy intake 

(21 MJ ME day -1 ) in early pregnancy may also reduce the litter size in sows fed very restricted 

(36 MJ ME day -1 ) during lactation. Pregnancy rate in gilts can apparently be reduced 

if they are fed very restricted (≤18 MJ ME day -1 ) the first 35 days of pregnancy. 

Whether this is the same for sows is not possible to conclude, however, it seems that low 

energy intake for several successive parities can increase the risk of being culled as a consequence 

of not being pregnant. Furthermore, it cannot be excluded that high feed intake 

during pregnancy reduces voluntary feed intake in lactation and thereby reduce the litter 

size in the following cyclus. 

The existence of a relation between energy intake and litter size and pregnancy rate is further 

supported by studies showing an effect of energy related hormones, e.g. insulin and 

IGF-1, on the hormonal control of litter size and pregnancy. The increase in ovulation rate 

seen in gilts as a consequence of flushing before oestrus is thus believed to be mediated 

through an increase in insulin and IGF-1 levels followed by an increase in plasma levels of 

38

- Paper I - 

gonadotrophins (LH, FSH) (Hughes & Pearce, 1989). Both LH and FSH act on the ovaries 

to stimulate the development of the pre-ovulatory follicle (Foxcroft & Hunter, 1985). LH is 

furthermore essential for the maintenance of early pregnancy in the pig (Peltoniemi et al., 

1995) why lower pregnancy rate as a consequence of restricted feed intake may be due to a 

reduction in LH pulse frequency (Peltoniemi et al., 2000). The negative effect of high feed 

intake the first three days in pregnancy on embryo survival is believed to be caused by an 

increase in hepatic blood flow and metabolic clearance rate of progesterone, as a consequence 

of rapid weight gain, followed by a decrease in plasma level of progesterone 

(Hughes & Pearce, 1989; Foxcroft, 1997). Progesterone is the primary director of uterine 

development and secretion (Geisert & Yelich, 1997) and therefore a change in plasma level 

of progesterone could imply detrimental consequences for embryo survival as indicated in a 

study by Pharazyn et al. (1991). Progesterone is secreted from Corpus Luteum and because 

the pig is polyovulatory, it is suggested that it is unlikely that the plasma progesterone concentration 

may get below some essential threshold after the first three to four days of pregnancy 

(Foxcroft, 1997). 

The statement, that reproduction may be influenced by nutrition is further supported by 

observations of wild sows. Matschke (1964 q.f. Graves, 1984) reported that European wild 

sows were anoestrous during years of small quantity of mast and similar did Mauget (1981) 

report that the timing of breeding season was influenced by the amount of mast available. 

When looking upon the results from the studies reviewed, although it does not provide a 

clear picture, it seems that pregnancy rate and litter size can be influenced by energy intake 

in the non-lactative period. However, the question, which remains to be answered, is 

whether variation in energy intake between female pigs in commercial group-housed systems 

reaches magnitudes large enough to impair the litter size and pregnancy rate? 

Andersen et al. (1999) observed that low ranking sows only spent about half as much time 

at the trough at feeding compared to high ranking sows (40 vs. 90 % of observations) in a 

group of pregnant sows. Although low ranking sows may be able to increase their eating 

rate when competition for feed is high, as suggested by Brouns & Edwards (1994), it is 

likely that the energy intake of the low ranking sows has been considerably lower than the 

energy intake of the high ranking sows. Mendl et al. (1992) observed that low and none 

success primaparous sows (the sows were divided into three groups according to their ability 

to displace other sows in agonistic interactions) had significant lower weight gain than 

high success primaparous sows (approximately 7, 9 and 19 kg, respectively in one month) 

in their 7 th week of pregnancy. As Mendl et al. (1992) point out, the lower weight gain in 

the low ranking sows is not necessarily a result of lower feed intake only but perhaps a 

combination of lower feed intake and an elevated expenditure of energy for maintenance as 

39

- Paper I - 

a consequence of stress. However, no matter what may have caused the lower weight gain, 

the result would be less energy substrates available for the physiological processes related 

to reproduction. In the study by Brouns & Edwards (1994), the weight gain throughout 

gestation in the low ranking sows was only 60% (28.3 vs. 46.6 kg) and 50% (22.4 vs. 44.9 

kg) of the weight gain of the high ranking sows, respectively in two different experimental 

pens. The total gain of 44.9 kg and 22.4 kg during an entire gestation corresponds with approximately 

0.390 kg and 0.195 kg daily gain, respectively. The groups consisted of multiparaous 

sows and the ranking order was significantly correlated with initial live weight of 

the sows (Brouns & Edwards, 1994). According to Danielsen (personal communication, 

2003), one kg of gain in gestation requires 14 MJ ME, for which reason 0.390 and 0.195 kg 

of gain would require 6 and 3 MJ ME, respectively. Assuming that high ranking sows 

weighted about 260 kg and low ranking sows 200 kg, the daily energy requirement for 

maintenance for high and low ranking sows would be approximately 27 MJ ME and 23 MJ 

ME, respectively (Just et al., 1983; Theil et al., 2002; Danielsen, personal communication 

2003). Estimated energy intake for low ranking sows would therefore be approximately 80 

% of the energy intake of the high ranking sows (26 and 33 MJ ME, respectively). 

In commercial practice, the difference between high and low ranking sows’ feed intake 

during pregnancy may, under some circumstances, be higher than indicated in the studies 

by Andersen et al. (1999) and Brouns & Edwards (1994). In these studies, the group size 

was six and 12 sows, respectively, whereas in commercial sow herds, floor feeding is also 

practiced in larger groups. If the feed is provided on a small area, it is likely that the more 

sows in the group, the higher the risk that the low ranked sows are kept away from the feeding 

place. Experiences from practical husbandry indicate that a huge variation in weight 

between sows causes more aggressions and displacements at feeding compared to more 

uniform groups (Olsson & Svendsen, 1997). Therefore, the magnitude of the variation in 

energy intake between group housed sows will probably not only depend upon feeding procedure 

but also on group size and group composition and then vary considerably between 

herds but also within herds between farrowing batches. 

It is generally recommended to feed pregnant sows in the range of 25-35 MJ ME day -1 

(NRC, 1998; The National Committee for Pig Production, 2003b). If sows for instance are 

provided with 30 MJ ME day -1 , and assuming that the low ranking sows only eat approximately 

50-80% of the portion that high ranking sows as indicated in the studies by 

Andersen et al. (1999) and Brouns & Edwards (1994), this means that high ranking sows 

would consume 33-40 MJ ME day -1 and low ranking sows 20-26 MJ ME day -1 in average. 

In gilts, an energy intake of 33-40 MJ ME day -1 could have a negative influence on litter 

size if it occurs the first three days after mating. An energy intake of 20-26 MJ ME day -1 

40

- Paper I - 

the first four weeks after mating could perhaps impair pregnancy rate in gilts and litter size 

in sows fed restricted during lactation. 

As regards before mating, it is not possible to say how huge impact the involvement in aggressive 

interactions has on a sow’s appetite and therefore whether variation in feed intake 

can influence the variation in litter size and pregnancy rate. Further studies are needed to 

clarify this. 

6. Conclusion 

Based upon a review of existing literature, it is suggested that pregnancy rate and litter size 

can be influenced by energy intake although the results reviewed do not provide a clear 

picture. There is little doubt, however, that the reproduction performance of the gilt, in general, 

is more influenced by energy supply than the reproduction performance of the sow. It 

is further suggested that variation in feed intake in a group of restricted fed pregnant female 

pigs in commercial pig husbandry, may be large enough to influence pregnancy rate and 

litter size. However, there is no empiricism to support this, why there is a need for studies 

analyzing whether a relation between individual feed intake and reproduction performance 

exists in a group of non-lactating female pigs. 

41

7. References 

- Paper I - 

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fasting on various reproductive phenomena of sows. J. Anim. Sci. 48, 359-362. 

Almeida, F.R.C.L., Kirkwood, R.N., Aherne, F.X., Foxcroft, G.R., 2000. Consquences of different patterns of 

feed intake during the estrous cycle in gilts on subsequent fertility. J. Anim. Sci. 78, 1556-1563. 

Andersen, I.L., Bøe, K., Kristiansen, A.L., 1999. The influence of different feeding arrangements and food 

type on competition at feeding in pregnant sows. Appl. Anim. Behav. Sci. 65, 91-104. 

Anderson, L.L., 1975. Embryonic and placental development during prolonged inanition in the pig. Am. J. 

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Arey, D., Edwards, S.A., 1998. Factors influencing aggression between sows after mixing and the concequences 

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Ashworth, C.J., Antipatis, C., 1999. Effect of pre- and post-mating nutrtion on embryo survival in gilts. Reproduc. 

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Baidoo, S.K., Aherne, F.X., Kirkwood, R.N., Foxcroft, G.R., 1992. Effect of feed intake during lactation and 

after weaning on sow reproductive performance. Can. J. Anim. Sci. 72, 91-917. 

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Beltranena, E., Foxcroft, G.R., Aherne, F.X., Kirkwood, R.N., 1991. Endocrinology of nutritional flushing in 

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Brouns, F., Edwards, S.A., 1994. Social rank and feeding behaviour of group-housed sows fed competitively 

or ad libitum. Appl. Anim. Behav. Sci. 39, 225-235. 

Brouns, F., Edwards, S.A., English, P.R., 1991. Fibrous raw materials in sow diets: Effects on voluntary food 

intake, digestibility and diurnal activity patterns. Anim. Prod. 52, 598. 

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Cosgrove, J.R., Foxcroft, G.R., 1996. Nutrition and reproduction in the pig: ovarian aetiology. Anim. Reprod. 

Sci. 42, 131-141. 

Cox, N.M., Stuart, M.J., Althen, T.G., Bennett, W.A., Miller, W., 1987. Enhancement of ovulation rate in 

gilts by increasing dietary energy and administering insulin during follicular growth. J. Anim. Sci. 64, 

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Csermely, D., Wood-Gush, D.G.M., 1990. Agonistic behaviour in grouped sows. II. How social rank affects 

feeding and drinking behaviour. Boll. Zool. 57, 55-58. 

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Stress and fear as possible mediators of reproduction problems in group 

housed sows: A review 

A.G. Kongsted 


8830 Tjele 

Acta Agric. Scand., Sect. A, Animal Science 54: 58-66, 2004 

49 

II

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Indicators of feed intake, fear and social stress in commercial herds with 

group housed non-lactating sows 

A.G. Kongsted, J.E. Hermansen and T. Kristensen 


8830 Tjele 

Submitted to Acta Agric. Scand., Sect. A, Animal Science 

59 

Ш

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Abstract 

A.G. Kongsted, J.E. Hermansen and T. Kristensen (Department of Agroecology, Danish 

Institute of Agricultural Sciences, P.O. Box 50, DK-8830 Tjele). Indicators of feed intake, 

fear and social stress in commercial herds with group housed non-lactating sows. Acta Agric. 

Scand., Sect. A, Animal Sci. 


of changed legislation. With the aim to evaluate indicators of feed intake, fear and 

stress and to get insight in the level and variation in these indicators in group housed sows 

under various on-farm conditions, a study took place including 14 herds. The results 

showed that back fat-, skin lesions- and behavioural measurements might be relevant indicators 

of sows’ condition at herd, batch and individual sow level. For almost all indicators, 

the variation between herds was larger than the variation between batches. The betweensow 

variation in back fat was significant higher in group- compared to individual feeding 

systems. For some of the indicators, the effect of parity differed between different layouts. 

For instance, in herds without escape possibilities, first parity sows had the highest level of 

lesions, whereas in herds with escape possibilities, second and third parity sows had the 

highest level. 

Keywords: Farm study, skin lesions, eating behaviour, aggressions, group feeding, individual 

feeding 

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of changed EU legislation (Council Directive 2001/88/EC amending Directive 

91/630/EEC Laying Down Minimum Standards for the Protection of Pigs) combined with 

extraordinary national laws (Baustad & Lium, 2002; The welfare of Farmed Animals (England) 

(Amendment) Regulations 2003). 

However, since individual housing of sows has been the far most common system in commercial 

sow herds for many decades, most of the information available about sows’ production 

and condition arrives from studies with individual housing. Although the amount of 

scientific work related to group housing of sows has increased markedly in the last ten 

years, there is still a lot of unanswered questions concerning the function of the sows in 

commercial herds with group housed non-lactating sows. 

Several experimental studies indicated that group housing of sows might lead to individual 

variation in feed intake, social stress, and fear (reviews by Kongsted, 2004ab). This may 

constitute a welfare problem and in addition affect the reproduction results negatively (reviews 

by Kongsted, 2004ab). Most of the studies referred to in the mentioned reviews were 

performed under conditions that did not always reflect those circumstances seen in practice 

which are large group sizes (Nielsen et al., 2000), high stocking rates (Svendsen et al., 

1990), constant introduction of new sows into dynamics groups (Svendsen et al., 1990), 

slippery floors (Hansen & Kongsted, 2002) and sows with locomotion problems (Gjein & 

Larssen, 1995; Nielsen et al., 2000; Hansen & Kongsted, 2002). 

In a few Danish on-farm experiments, level and variation of indicators of feed intake expressed 

as growth rate (Fisker, 1994; Nielsen, 1995; Fisker, 1999; Hansen, 2000) and stress 

expressed as adrenocortical response to additional stressors (Jensen et al., 1995) in group 

housed sows has been assessed. However, systematic information of variation in feed intake, 

fear and social stress in sows group housed in the entire non-lactating period under 

various conditions are lacking. This is most likely, to some extent, because traditional 

methods for assessing these factors are expensive and/or time-consuming and therefore 

difficult to employ under practical conditions in large scale. First of all, it is therefore necessary 

to identify indicators of energy intake, stress and fear suitable for use in practice. 

Based upon existing knowledge, a suggestion for such indicators has been put forward in 

Kongsted (2004a). However, whether these indicators are suitable for use in group housed 

sows under various on-farm conditions is not known. 

On this background the aim of this study is 1) to evaluate indicators believed to be suitable 

to gain information of variation in feed intake, social stress and fear in non-lactating sows 

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group housed under different on-farm conditions and 2) to get insight in the level and be- 

tween-farm and within-farm variation in indicators of energy intake, fear and social stress 

in non-lactating sows group housed under various on-farm conditions. 

2. Materials and methods 

2.1 Herds, sows and design of recordings 

The study was conducted during an 11-month period from May 2003 to March 2004 in 

fourteen Danish commercial sow herds with group housed non-lactating sows. The herds 

were chosen to represent different layouts and management routines. The herd sizes varied 

from 180 to 1000 sows. Farrowing batch interval was 1, 2 and 2½ week in six, five and 

three herds, respectively. In all herds, the sows were moved to the service department and 

grouped on the day of weaning or the day after. One herd had integrated service and pregnancy 

department. In all other herds, the sows were moved to the pregnancy department 

between 0 to 28 days after first mating. In Table 1 the layout of the herds are detailed. It 

appears e.g. that eight of the 14 herds practiced group feeding (biofix, on the floor and long 

feeding troughs) in the pregnancy unit. 

Four batches were observed on each farm from weaning to farrowing. In each of the four 

batches, ten focal sows (F-sows) were randomly chosen in the lactation department just 

before the sows were moved to the service department on the day of weaning. In those 

herds where the sows were divided into different pens according to size (small, normal, 

large) in the service department the farmer marked the ‘normal’ sows the day before weaning 

and the ten F-sows were then chosen randomly from this group of sows. This procedure 

was carried out to ensure that all F-sows were placed in the same pen (or at least in adjacent 

pens) to make sure that it was possible to observe all F-sows at the same time. To allow 

individual identification during behavioural observations, the ten F-sows were sprayed with 

a number on their back and sides. 

62

Table 1. Applied feeding and housing systems in the service and the pregnancy unit of 14 farms 

Feeding system No. herds in total Ad lib. No. of daily Feed type Floor type Group dynamics Group size 

feeding feedings 

1 ≥2 Dry Liquid Concrete Deep lit- Stable Dynamic

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2.2 Registration of indicators 

2.2.1 Eating behaviour 

Although eating speed may differ between sows (Brouns & Edwards, 1994), behavioural 

observations of time spend eating is likely to give some indications of feed intake 

(Andersen et al., 1999). 

For each F-sow, it was recorded whether the sow was eating or not for each half minute 

during feeding. A sow was considered eating if she, while chewing had her snout in the 

trough or in contact with the floor (Csermely & Wood-Gush, 1990). However, if the sow 

shortly lifted her head from the trough or floor still chewing, she was also considered eating. 

The recordings began the moment the feed was supplied and stopped 25 minutes (50 

recordings) after or until the last sow had stopped eating. Number of times the sow was not 

eating compared to number of recordings (max 50) was calculated for each F-sow (% not 

eating). 

2.2.2 Back fat depth and back fat gain 

Measurements of back fat depth is a method to assess the body condition of sows (Charettte 

et al., 1996 fra livestock s. 4) and is possible to perform also under practical conditions 

(pers.comm., Maes, 2004). 

Back fat depth was measured on the F-sows by means of a digital ultrasound back fat indicator 

LEAN MEATER ® (Baltic Korn A/S, Naestved, Denmark). All measurements were 

performed in the home pen of the sow i.e. in a farrowing crate (at weaning and at farrowing) 

or in a group of sows (three weeks after mating). The back fat was measured about 65 

mm from either side of the backbone at the 10 th and 12 th (last) rib (conventionally known as 

P2-measurements) and all three layers of fat was measured. Four measurements were performed 

in all (two at each rib). The average value of the four measurements was used to 

characterise the back fat depth of the sow. Observations with more than five mm deviations 

between the lowest and highest measurement were excluded from the material (15 sows). 

Back fat gain per day were calculated as the difference between back fat at the beginning of 

the period and back fat at the end of the period divided with the number of days between 

the two measurement days. 

2.2.3 Fear tests 

Three examples of fear tests believed to be possible to perform in commercial sow herds 

were used in this study. These test are further discussed in Kongsted (2004a). 

At weaning, when the F-sows were routinely moved from the service to the pregnancy department, 

a human approach test (HA-test) (Rousing et al., 1999; Bonde et al., 2003) was 

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performed. The sow had to pass a human (a research technician) at a passage of 10 metres 

long and about one meter wide. The relation between the time required to approach the per- 

son (AB) compared to the total time required to pass the 10 metres (AC) was calculated 

(=AB/AC). If the sow had not passed the 10 metres after two minutes the test was stopped. 

If the AB was more than two minutes the value of AB/AC was specified as 1. Sows with 

AB/AC values of > 0.67 were categorized as fearful. 

In the home pen of the F-sows, a forced human approach (FHA-test) (Andersen et al., 

2003) was performed. A research technician entered the home pen quietly, approached the 

sow and squatted down immobile 20 cm from the sows for 30 seconds. The sow’s reaction 

was categorised into one of six possible reactions: 1. Fled at a distance of more than 1 m 

from the technician, 2. Withdrew some steps away from or turned her head away from the 

technician, and stayed there ore continued with activity for the rest of the test period, 3. 

Withdrew some steps away from or turned her head away from the technician, but approached 

the technician again and initiated physical contact within the test period, 4. Neither 

withdrew from nor approached the technician, but remained in the same posture or 

continued with activity, 5. Remained in the same posture or continued with activity, but 

seeked contact with the technician before the end of the test period or 6. Approached and 

initiated physical contact with the technician (pers. comm., Andersen 2003). Sows with 

reaction 1 or 2 were categorized as fearful. 

After the FHA test a forced human touch test (FHT-test) (Pedersen et al., 2003) was performed. 

The technician approached the head of the sow and touched or tried to touch the 

sows neck. The sows reaction was divided into three reactions: 1. Fled before touching her 

neck was possible/fled with or without squaling/stood immobile holding the head still while 

keeping the eyes fixed, 2. Walked away without squealing or 3. Stood calmly/moved the 

head towards the technician/approached the technician (Pedersen et al., 2003). Sows with 

reaction 1 were categorised as fearful. 

The FHA and the FHT tests were performed outside the sows’ expected resting period. 

Based upon previous studies (Jensen et al., 1996) and statements from the individual farmers, 

resting period was chosen as between 11 and 13 PM in all 14 herds. 

Sows may use feeding stalls as an escape possibility during fighting (Olsson & Samuelsson, 

1993 cf. Arey & Edwards, 1998) and frequency of reside in stalls may reflect level of fear 

towards the other sows in the group. Therefore, for each F-sow, it was recorded whether the 

sow was in box or not for each 10 minute the first hour after weaning and half an hour at 

mating and three weeks after mating. Number of times the sow was in box compared to 

number of recordings (7 or 4) was calculated for each F-sow (% in box). 

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2.2.4 Aggressive interactions, skin lesions and lying solitary 

Involvements in aggressive interactions (Barnett et al., 1981; Mendl et al., 1992), skin le- 

sions (Barnett et al., 1992) and frequency of lying solitary during resting periods (Barnett et 

al., 1984; Bonde, 2004) were used as indicators of stress. For a discussion of why these 

parameters are believed to be suitable indicators for stress, see review by Kongsted (2004a). 

The first hour after weaning and half an hour at mating and three weeks after mating outside 

the resting period, the number of aggressive interactions the individual sow participated 

in was recorded. An interaction was defined to have occurred when one sow initiated 

a behaviour, which was clearly directed at another sow in the group (Bradshaw et al., 

2000). All interactions were categorised into four different types: 1) a threat, 2) one 

bite/knock/push, 3) several bites/knocks/pushes and 4) bites from both sows (Jensen et al., 

1996; Bradshaw et al., 2000; Jensen et al., 2002). 

The total number of skin lesions divided into four length categories (10 

cm) on head, ears, neck and shoulders (Barnett et al., 1992) were recorded for all F-sows by 

a research technician. All lesions (except shoulder wounds because they are not a result of 

aggressive interactions) were recorded (also superficial scratches). The recordings were 

performed in the home pen of the F-sows, i.e. in a group of sows. Total length was calculated 

as total number in the length category 1-4 multiplied with 0.5, 2.5, 7.5 and 10 respectively. 

The behaviour of the F-sows was recorded during resting period for 25 minutes. Every five 

minute the position of the individual sow (in a feeding stall, in the dung area, in the resting/activity 

area) was recorded and the ten F-sows’ behaviour were categorised into the 

following: 1) lying/sitting solitary, 2) lying/sitting socially or 3) standing/walking/running 

(if a sows position was a feeding stall her behaviour was not recorded). Lying/sitting solitary 

was defined as lying/sitting in a distance of 20 cm or more from other sows (Bonde, 

2004). If the sow was lying/sitting more frequently than not, the sow was categorised as 

lying. If the sow was lying/sitting solitary more frequently than lying/sitting socially, the 

sow were categorised as lying solitary. 

2.3 Timing and frequency of recordings 

The timing of registrations were first of all chosen to give information of the sows’ conditions 

from weaning to first mating and from first mating to three weeks in pregnancy because 

these phases seems to be the main periods of relevance regarding reproduction performance 

(Kongsted, 2004ab). The timing of the above mentioned recordings and measurements 

are presented in Table 2. The recordings took place at weaning, at mating, ap- 

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proximately three weeks after first mating or just before the following farrowing. Only 

sows, pregnant after first mating were followed all the way to the following farrowing. 

Table 2. Time schedule of measurements/recordings (number of herds in parenthesis) 

Indicator 

Measurements/recordings 

Day of weaning At mating 

(W) 

1) 

After weaning 

(M) 

2) 

At farrowing 

(AM) 

(F) 

Back fat X (14) - X (14) X (14) 

Eating behaviour X (2) X (2) X ( 9) - 

Fear test (HA) X (14) - - - 

Fear test (FHA and FHT) - - X (14) - 

Aggressions and % in box X (14) X (4) X (13) - 

Lesions X (14) X (14) X (14) X (14) 

Lying behaviour X (14) X (4) X (13) - 

1) 4-7 days after weaning 2) 20-28 days after weaning 

In ten herds the sows were fixed in feeding stalls in the days or hours around insemination 

why it was not possible or relevant to record eating and resting behaviour or to perform fear 

tests. For three farrowing batches in two different herds it was impossible to perform the 

human approach test when moving sows routinely at weaning because no suitable testing 

area was available. The two fear tests (FHA and FHT) were not performed at mating because 

it turned out to be very difficult to perform on sows in oestrus. Sows in oestrus were 

in general very contact seeking, which made the results unreliable and sometimes endangered 

the test person! In one herd, the large group sizes and the layout of the stables made it 

impossible to overview the ten F-sows resting behaviour three weeks after mating. Measurement 

of eating behaviour was only performed in herds with group feeding. 

2.4 Statistical analysis 

All analyses were based on data from individual sows. Parity was divided into three groups: 

1. First parity sows 2. Second and third parity sows and 3. Sows older than third parity. 

First parity sows were defined as sows that had weaned one litter when entering the service 

unit. 

The layout of the mating unit was divided into +/- escape possibilities (defined as +/- access 

to feeding stalls) whereas the pregnancy unit were categorised as group vs. individual feeding 

or +/- escape possibilities (defined as group sizes above 30 or access to feeding stalls). 

When analysing the effect of parity and layout, the following mixed model was applied: 

E(Yijklm )= µ + αi + βj + (αβ)ij + a·xijklm + Ak(j) + Bl(kj) 

In which Yijklm is the observed independent variable transformed by the natural logarithm 

(skin lesions), square root (% not eating and aggressions) or logit (% in box). E() indicates 

expected value. In case of the dichotomous categorical variables E(Yijklm) corresponds to 

logit to the probability of the observed outcome, pijklm. µ is the overall mean of the observa- 

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tions, αi is the fixed effect of parity group, βj is the fixed effect of layout, (αβ)ij is the interac- 

tion between parity group and layout, xijklm is the back fat at weaning or three weeks after 

mating, a is the regression parameter, Ak(j) and Bl(kj) are the normal distributed random ef- 

fects of herd (within layout) and batch (within herd) respectively. For all continuous indica- 

tors, Yijklm ~ N(E(Yijklm), σijklm 2 ) whereas for all categorical indicators, Yijklm ~ B(1, pijklm). 

The covariate xijklm was only included in the model of the indicator back fat gain. Further, 

when analysing the effect of herd and batch, βj and (αβ)ij were excluded. Effects with Pvalues 

above 0.10 were eliminated from the model one by one and the analysis was repeated. 

For all continuous indicators, the statistical analyses were performed with a linear mixed 

model using the MIXED procedure (Littell et al., 1996) in SAS ® (SAS Institute Inc. 1990). 

For all categorical indicators, the statistical analyses were performed with a generalized 

linear mixed model using the glmmPQL function in the MASS package (Venables & Ripley 

2002) of R (R Development Core Team 2004). Effect of herd and batch within herd 

(random effects) were analysed by a Wald Z-test that provides an approximate test that the 

variance components are zero. For all continuous indicators, this was done by including the 

option COVTEST in the MIXED procedure (Littell et al., 1996), and a similar test was calculated 

in R. The test for variance heterogeneity (test for different between-sow variation in 

herds with group feeding and herds with individual feeding) for all back fat measurements 

was performed by comparing a model with homogeneous covariance structure to a model 

with heterogeneous covariance structure by means of the likelihood ratio test. For all continuous 

indicators, the option GROUP in the MIXED procedure was used to specify heterogeneity 

in the covariance structure (Littell et al., 1996). 

The correlation between continuous indicators was calculated using the CORR procedure 

(SAS Institute Inc. 1990). The calculations were based on data transformed to obtain normality 

and corrected for herd and batch mean. 

3. Results 

For all continuous indicators, the overall averages and different measurements of the variation 

between sows across all 14 herds are presented in Table 3. For all lesions- and aggressions 

measurements, the 50% quantile was lower than the mean value, which indicates that 

these variables were not normally distributed but skewed to the right. 

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Table 3. Overall mean and variation shown as the standard deviations (Std), the minimum (Min) and 

maximum (Max) values, the median (M50) and the 5% (Q5) and 95% (Q95) quantiles for all continuous 

indicators (sow level) 

N Mean Std Min Max M50 Q5 Q95 

Back fat W mm 551 15 5 6 35 14 9 23 

Back fat AW mm 524 16 4 7 34 15 10 24 

Back fat F mm 428 18 6 6 43 17 10 30 

Back fat gain W → AM mm/day 481 0.03 0.07 -0.19 0.27 0.03 -0.08 0.16 

Back fat gain AM → F mm/day 387 0.03 0.04 -0.11 0.17 0.02 -0.03 0.1 

Not eating W % 19 54 - 0 98 52 0 98 

Not eating M % 62 46 - 0 100 47 4 92 

Not eating AM % 299 27 - 0 100 21 0 74 

Lesions W cm 554 3 - 0 162 0 0 14 

Lesions M cm 542 66 - 0 330 48 3 181 

Lesions AM cm 543 76 - 0 384 63 6 197 

Lesions F cm 456 46 - 0 249 31 0 143 

Lesions W no. 554 2 - 0 100 0 0 12 

Lesions M no. 542 28 - 0 171 23 1 72 

Lesions AM no.. 543 37 - 0 208 30 3 86 

Lesions F no. 456 26 - 0 188 18 0 78 

Aggressions W no. 552 4.0 - 0 66.0 3 0 13 

Aggressions M no.. 99 0.7 - 0 7.0 0 0 3.0 

Aggressions AM no. 479 1.5 - 0 21 1 0 5 

Aggressions int 3+4 1) W no. 552 2.5 - 0 36 2 0 8 

Aggressions int 3+4 1) M no. 99 0.3 - 0 3 0 0 2 

Aggressions int 3+4 1) AM no. 479 0.3 - 0 6 0 0 2 

% in box W % 348 63 - 0 100 71 0 100 

% in box AM % 74 95 - 0 100 100 75 100 

W: Weaning M: Mating AM: Three weeks after mating F: Farrowing 

1) Only serious interactions, 3 (several bites/knocks/pushes) and 4 (bites from both sows). 

The variation cannot be presented as variation between sows for all lying and fear measurements 

because these indicators are categorical. Instead the variations of these indicators 

are presented as the variation between batches (Table 4). 

Table 4. Mean and variation shown as the minimum (Min) and maximum (Max) values, the median 

(M50) and the 25% (Q25) and 75% (Q75) quantiles for all categorical indicators (%sows per batch) 

N Mean Min Max M50 Q25 Q75 

Lying W 56 26 0 100 20 10 40 

Lying AM 52 68 0 100 80 55 90 

Lying alone W 52 25 0 30 10 0 11 

Lying alone AM 55 8 0 70 20 10 30 

Fear test (HA) 53 30 0 90 22 10 50 

Fear test (FHA) M 8 63 22 100 72 30 89 

Fear test (FHA) AM 56 47 0 100 50 30 60 

Fear test (FHT) M 8 49 0 89 50 34 71 

Fear test (FHT) AM 56 48 0 100 50 30 66 

W: Weaning M: Mating AM: Three weeks after mating F: Farrowing 

3.1 Relation between indicators 

The correlations between the indicators are shown in Table 5. Back fat measured at different 

times were highly correlated. Further, although less pronounced, correlations between 

back fat and back fat gain existed. High back fat at weaning was negative correlated with 

back fat gain from weaning to three weeks after weaning but positive correlated to back fat 

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gain from three weeks after mating to farrowing. The skin lesion measurements, taken at 

different times were also significant interrelated. 

Also significant correlations between different indicators existed. Back fat measured at all 

three stages were e.g. negatively correlated to lesions (both number and length) three weeks 

after weaning and at the following farrowing. Aggressions at weaning were positive correlated 

to back fat gain, but negatively correlated to % not eating and lesions. This indicates 

that sows, involved in few aggressions at weaning have a low feed intake and receive many 

aggressions during pregnancy. 

70

Table 5. Correlations between all continuous indicators (transformed to obtain approximate normality and corrected for herd and batch mean). Correlations 

in bold are significant 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

Back fat. mm 

1. W *** *** *** ** ns ns ns ns * ** ns * * ns ns ns ns ns 

2. AM 0.85 *** *** ** ns ns ** ns *** *** ns ** *** ns ns ns ns ns 

3. F 0.70 0.75 ** *** ns ns *** ns *** *** ns *** *** * ns ns ns ns 

Back fat gain, mm/day 

4. W to AM -0.23 0.23 0.20 ns ns ** ** ns ** ns ns ** ns ** ** ns ns ns 

5. AM to F 0.14 0.15 0.68 0.02 ns ns ** ns ** *** ns *** *** * ns ns ns ns 

Not eating, % 

6. W 0.36 0.25 0.19 -0.08 -0.16 ** ns ns ns ns ns ns ns ns ns * - - 

7. M 0.34 0.05 0.01 -0.43 -0.01 0.85 ns ns ns ns ns ns ns ns * ns - - 

8. AM -0.09 -0.18 -0.30 -0.20 -0.27 0.24 0.15 ns *** ns ns *** ns ** ns ns ns - 

Lesions, cm 

9. M -

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3.2 Between-farm and within-farm variation of indicators 

In Figure 1, the variation between herds and between batches within herds are shown for 

some of the indicators and in Table 6, the effects of herd and batches are given. 

Table 6. Effect of herd and farrowing batch within herd on level of indicators 

Variance component % of variation explained Significance 

Herd (σk 2 ) Batch (σl(k) 2 ) Sow (ε ) Herd Batch Sow Herd Batch 

Back fat W 1.8 2 1.1 2 4.0 2 16 5 79 * * 

Back fat AM 1.5 2 1.2 2 3.8 2 12 8 80 * * 

Back fat F 2.8 2 0 5.0 2 23 0 77 * - 

Back fat gain W → AM 0.01 2 0.02 2 0.06 2 5 8 87 ns * 

Back fat gain AM → F 0.02 2 0.008 2 0.03 2 31 5 64 * ns 

Lesions, No. M 0.6 2 0.4 2 0.9 2 28 9 63 * ** 

Lesions, No. AM 0.5 2 0.4 2 0.8 2 24 14 62 * ** 

Lesions, No. F 1.1 2 0.3 2 1.0 2 52 5 43 ** * 

% not eating AM 1.3 2 0.7 2 1.9 2 29 7 64 * * 

Aggressions W 0.5 2 0.4 2 0.9 2 22 11 67 * ** 

Aggressions AM 0.4 2 0.3 2 0.7 2 22 10 67 * ** 

% in box W 0.6 2 0.8 2 2.1 2 7 12 81 ns * 

Lying alone W 0.9 2 1.0 2 - a) 45 55 - a) ** *** 

Lying alone AM 0.7 2 0.03 2 - a) 99

Back fat W, mm 

Back fat gain, AM-F, mm/day 

Skin lesions AM, no. 

30 

25 

20 

15 

10 

5 

0 

0,12 

0,07 

0,02 

-0,03 

-0,08 

-0,13 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314 

Figure 1. Variation between the four batches within the 14 herds 

Back fat AM, mm 

% not eating AM 

Skin lesions F, no. 

30 

25 

20 

15 

10 

5 

0 

70 

60 

50 

40 

30 

20 

10 

0 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314 

Back fat F, mm 

Aggressions W, no. 

Fear test (HA), % sows 

30 

25 

20 

15 

10 

5 

0 

20 

15 

10 

5 

0 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314 

Back fat gain W-AM, mm/day 

Skin lesions M, no 

Fear test (FHA), % sows 

0,12 

0,07 

0,02 

-0,03 

-0,08 

-0,13 

1 2 3 4 5 6 7 8 9 10 1112 1314 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

100 

90 

80 

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60 

50 

40 

30 

20 

10 

0 

1 2 3 4 5 6 7 8 9 1011121314 

1 2 3 4 5 6 7 8 9 1011121314

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Table 7. The between-sow variation in back fat measurements in herds with group feeding and herds 

with individual feeding 

Variance component (variation between sows) 

Group Individual Significance 

Back fat W 4.2 2 3.5 2 * 

Back fat AM 3.9 2 3.6 2 NS 

Back fat F 5.6 2 3.9 2 *** 

Back fat gain W → AM 0.069 2 0.055 2 ** 

Back fat gain AM → F 0.037 2 0.024 2 *** 

W: Weaning AM: Three weeks after mating F: Farrowing 

*. **. ***: Significant effect (P=

- Paper III - 

from three weeks after weaning to farrowing, no effect of back fat three weeks after mating 

(P>0.1), feeding system (P>0.1) or interaction between parity and feeding system (P>0.1) 

was found. 

As shown in Table 9, % not eating three weeks after mating differed significantly between 

parity groups (P=0.01) in that sows older than third parity were spending more time eating 

compared to younger sows. 

75

Table 8. Effect of parity on back fat at weaning, three weeks after mating and at farrowing and back fat gain from weaning to three weeks after mating in 

herds with group feeding and herds with individual feeding shown as LS-MEANS and number of sows 

Feeding system Parity group 

Back fat W 

LS-MEANS n 

Back fat AM 

LS-MEANS n 

Back fat F 

LS-MEANS n 

Back fat gain W→AM 

LS-MEANS n 

1 13.1 (84) 13.5 (79) 16.2 (53) 0.012 (72) 

Group 

Individual 

2 14.8 (141) 15.9 (131) 18.44 (115) 0.042 (123) 

3 17.3 (87) 18.3 (87) 22.2 (72) 0.062 (80) 

1 13.6 (69) 14.4 (68) 17.0 (51) 0.019 (65) 

2 14.4 (76) 15.3 (74) 17.0 (60) 0.026 (65) 

3 14.8 (93) 16.0 (88) 17.6 (77) 0.029 (75) 

P-value (parity group x feeding system)

- Paper III - 

Number of skin lesions. The number of skin lesions at mating were significant lower in 

herds with escape possibilities compared to herds without escape possibilities in the mating 

unit (13.7 vs. 30.9, n=400 vs. 142, P=0.01). There was no effect (P>0.1) of parity group and 

no interaction (P>0.1) between +/- escape possibilities and parity group for number of le- 

sions at mating. 

There was a significant interaction between parity group and escape possibility in the pregnancy 

unit for number of skin lesions three weeks after mating (P0.1) was found on aggressions 

three weeks after mating and no parity group x escape interaction (P>0.1). There 

was no effect of parity group on % in box at weaning (P>0.1). 

Lying behaviour. As shown in Table 9, parity group affected the probability of lying solitary 

at weaning (p=0.04) in that, the probability of lying solitary was higher for sows older 

than third parity compared to younger sows. There was no effect of +/- escape possibilities 

(P=0.6) on lying solitary at weaning and no effect of parity group (P=0.3), +/- escape possibilities 

(P=0.6) or interaction (P=0.4) for lying solitary three weeks after mating. 

Fear tests. In the HA-test test, first litter sows were more likely to be tested fearful compared 

to the other parity groups (P=0.03) as shown in Table 9. No main effect of parity 

group (P= 0.3, 0.4), +/- escape possibilities (P=0.5, 0.4) or interaction between parity group 

and +/- escape possibilities (P=0.3, 0.8) were found for the FHA-test or the FHT-test, respectively. 

4. Discussion 

With a few exceptions as mentioned in 2.3, the indicators were possible to perform in 

commercial sow herds at the planned stages at weaning, mating, three weeks after mating 

and/or at the following farrowing. 

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Almost all indicators were influenced by herd and batches within herd. This suggests that 

the indicators are sensitive to herd- and batch-specific factors. Furthermore, it seems that all 

indicators, except % in box, lying solitary three weeks after mating and the two fear tests 

performed three weeks after first mating were sensitive to the sow-specific factor, parity. 

With the above-mentioned and the theoretical background (Kongsted, 2004a) in mente, 

there are indications that the back fat measurements, the skin lesion assessments and the 

behavioural observations might be relevant indicators of the sows’ condition especially in 

relation to feed intake, stress and fear at herd, batch and individual sow level in commercial 

herds with group housed non-lactating sows. 

For almost all indicators, the variation between herds was larger than the variation within 

herd between batches. This suggests that factors that might differ between herds, e.g. layout, 

management and genetics, influence the indicators more than factors which might differ 

between batches like e.g. climatic conditions. When the layout factors employed in the 

later analyses were taken into account, the percentage of variation explained by herd decreased 

only with a few percentage points (

- Paper III - 

In herds practising group feeding in the pregnancy department, back fat at farrowing de- 

creased significantly with decreasing parity number. This was not the case in herds with 

individual feeding. Since the same pattern was seen already at weaning, this may partly be a 

result of the sows’ condition at weaning more than a result of the sows condition throughout 

the non-lactating period (qua the high correlations between the back fat measurements 

between different measurement day). However, as the interaction between system and parity 

group became more and more significant for every day of measurement, it indicates that 

high-parity sows are favoured in herds with group feeding to a much larger extent compared 

to herds with individual feeding. This is further supported by the higher increase in 

back fat gain from weaning to three weeks in pregnancy with increasing parity group seen 

in the group feeding systems. The effect of parity group on back fat gain from three weeks 

after mating to farrowing did not differ between feeding systems. However when including 

the interaction, although the non-significance (P=0.17) the same trend was seen (results not 

shown). In addition, the behavioural observations showed that sows older than third parity 

spend significant more time eating compared to first to third parity sows in the group feeding 

herds. 

As several studies have found a positive correlation between parity and rank (Arey & Edwards, 

1998), it seems that the low ranked sows had less access to feed compared to the 

older high ranked sows in group feeding systems. This is supported by results from a previously 

field study that indicated lower feed intake in low compared to high ranking sows, as 

indicated by less increase in chest girth (Olsson & Svendsen, 1997). Also several experimental 

studies have indicated lower feed intake in low compared to high ranking sows in 

group feeding systems, as indicated by lower weight gain (Brouns & Edwards, 1994; Ruis 

et al., 2002), less time spend at the central area of the pile of feed provided on the floor 

(Csermely & Wood-Gush, 1990) and less time spent at the trough (Andersen et al., 1999). 

The result of the back fat measurements implies that group fed sows in average are provided 

with a larger amount of feed compared to individual fed sows probably in an attempt 

to achieve that all sows, also the low ranked get adequate amount of feed during pregnancy. 

The results of this study indicate an overfeeding of sows older than third parity more than 

an underfeeding of the young sows when looking upon average data. However, in the herds 

with group feeding, six % of all sows had back fat depth less than 10 mm at farrowing. In 

addition, in the group feeding systems, 11 out of 256 sows ate less than 20 % of all observations 

during feeding and four sows did not eat at all three weeks after mating. In this 

study, all the sows in the group feeding herds were fed amounts of feed below their capacity 

for feed intake during pregnancy (Brouns et al., 1991). It is therefore presumable that 

the majority of sows were motivated to eat (Jensen et al., 2000) and that sows, which did 

not eat were displaced from the feed or ‘chose’ to stay away to avoid aggressions. Taken 

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together, the results from this study indicate a serious welfare problem for a few sows that 

are not able to cope in this kind of system. Also, the apparently overfeeding of the older 

sows may constitute both a welfare- and productivity problem. Locomotion problems 

(Dourmad et al., 1994) and a low feed intake during lactation, which may reduce ovulation 

rate and embryo survival (Zak et al., 1997; Han et al., 2000) and perhaps even conception 

rate (Hughes et al., 1984) are well-known consequences of high feed intake during pregnancy. 

It is therefore of outmost importance that managers of group feeding systems try to 

avoid this unequal feed allocation. Possible management initiatives might be assuring sufficient 

‘isolation pens’ for sows, which are not able to cope in the system, providing the feed 

on a larger area in systems with floor feeding. In systems with liquid feeding, setting up 

body partitions may have a positive effect (Andersen et al., 1999), however, it presupposes 

that the feed are equally divided in the trough, which is difficult to achieve in practice 

(Olsson et al., 1993). 

Aggressions, skin lesions and lying behaviour. Since it is well known that mixing of unfamiliar 

sows causes fighting between sows to settle social ranking (Arey & Edwards, 1998) 

it is not surprising that the level of aggressions were highest on the day of weaning. The 

first hour after mixing, the individual sow was in average involved in four aggressions, 

varying from 0 to 66. The study indicates that feeding stalls have a reducing effect on aggressions 

the first hour after mixing, as also found in a previous experimental study 

(Barnett et al., 1992). In view of the fact that sows in average spend 63 % of all observations 

in box the first hour after mixing; this is not surprising. Irrespective of layout, sows 

older than third parity were involved in more aggressions compared to younger sows the 

first hour after mixing. As sows had access to feeding stalls in the majority of herds, one 

explanation for this could be that the lower ranked sows stayed in the stalls during the most 

serious hierarchical fights to avoid aggressions. 

In general, as also found in other field studies (Gjein & Larssen, 1995; Andersen & Bøe, 

1999; Leeb et al., 2001), the skin lesions were mainly superficial lesions. The total number 

and length of skin lesions approximately five days after mixing was 28 and 66 cm respectively. 

In an experimental study with comparable scoring method it was found that number 

of skin lesions varied in average from 11.1 to 17.0 and length of skin lesions in average 

from 19.4 to 28.0 cm ten days after mixing in sows group housed in various pen designs 

(Barnett et al., 1992). The level of skin lesions has been assessed in several field studies (de 

Koning, 1985; Gjein & Larssen, 1995; Olsson & Svendsen, 1997; Andersen & Bøe, 1999; 

Leeb et al., 2001), however, due to differences in measurement and scoring methods it is 

difficult to use the results of these studies as comparison. 

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Previous work have found that mixing of sows into small groups (12 and 3 sows respec- 

tively) lead to the highest level of skin injuries (Olsson & Svendsen, 1997) and the highest 

and longest lasting elevated level of cortisol (Tsuma et al., 1996) in low ranked sows. In 

contrast, Mendl et al. (1992) reported that if sows where mixed into a large group (37 gilts), 

the intermediate sows received the highest level of aggressions and had the highest level of 

cortisol. The dominating sows received the lowest level of aggressions and the submissive 

sows were in between. These results indicate that when little free space is available, the 

submissive sows are the ones receiving most aggressions probably because they receive 

aggressions from both the dominating and the intermediate sows, whereas the intermediate 

mainly receives aggressions from the dominating sows. In contrast, in large groups the 

most submissive sows have more chances to avoid the more dominant sows due to more 

available free space. Accordingly, this study found that in herds with no escape possibilities 

(small group sizes and no feeding stalls) in the pregnancy unit, first parity (and probably 

low ranked) sows had significant more lesions compared to older sows three weeks after 

mating and at farrowing, whereas in herds with escape possibilities, the second-third parity 

(and probably middle ranked) sows had the highest number of skin injuries. 

Although not significant, more skin lesions were observed in herds with escape possibilities 

in the pregnancy unit, especially at farrowing. One explanation for this could be that the 

group of herds with escape possibilities include the two herds with ESF and large dynamic 

groups with constantly introduction of new sows into the group. As seen in Figure 1, these 

two herds (herd 7 and 15) had the highest level of lesions at farrowing. This is in agreement 

with Leeb et al. (2001) who found significant more lesions in herds with dynamic groups 

compared to herds with stable groups in a field trial that involved 55 herds and O'Connell et 

al. (2003) who found a higher injury level in dynamic compared to stable groups in an 

experimental study. 

In accordance with Olsson & Svendsen (1995), the frequency of lying solitary was highest 

on the day of weaning. Further, the likelihood of lying solitary at weaning was highest for 

sows older than third parity, which were also the sows involved in most aggressions at 

weaning. Accordingly, Bonde (2004) found that solitary lying behaviour was positive correlated 

to involvement in aggressive interactions. Since there was no effect of parity group 

on the probability of lying at weaning (P=0.8, results not shown) the results was not solely 

a consequence of old sows lying more often than younger sows. 

Fear tests. According to the results from the human approach test performed at weaning, 

first parity sows were more likely to be categorised as fearful compared to older sows. This 

trend could however not be rediscovered in the two fear tests three weeks after mating in 

the home arena of the sows. The test arena for the human approach tests differed inevitable 

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between the 14 herds. As system differences previously have shown to influence the results 

of human approach tests (Marchant-Forde et al., 2003), the between-herd variation should 

be interpreted with caution. 

For managers of herds with group housed sows, information of the sows' condition would 

be very useful in relation to analysing and improving animal welfare and perhaps also productivity. 

Since it is likely that the sows’ general condition, to a large extent is influenced 

by management related factors, it may be difficult to predict the presence of e.g. stress, fear 

and unequal feed intake merely on the knowledge of layout related factors like feeding system 

and escape possibilities. Therefore, it seems important that managers are able to make 

an on site judgement of the sows’ condition. The indicators presented in this paper are possible 

to perform in practice, and taken together the results indicate that they could be relevant 

indicators of social stress, fear and feed intake. As a consequence, these indicators 

might be relevant ingredients of a management tool to analyse and improve the welfare and 

productivity of group housed sows. 

Acknowledgements 

The authors wish to thank the participating farmers and the technicians Henrik K. Andersen, 

Kristine R. Hansen, Michael Hansen, Orla Nielsen, Niels H. Thomsen, and Helge Yde 

for their much appreciated assistance in carrying out the data collection. The authors also 

wish to express their gratitude to Erik Jørgensen for valuable contributions to the statistical 

analyses. 

82

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Relation between reproduction performance and indicators of feed intake, 

fear and social stress in commercial herds with group housed nonlactating 

sows 

A.G. Kongsted 


8830 Tjele 

87 

ІV

- Paper IV - 

Abstract 

Group housing of non-lactating sows is becoming more and more widespread in commercial 

sow herds in several European countries as a result of changed legislations. Results 

from experimental studies suggest that group housing may lead to individual variation in 

feed intake, stress and fear, which may impair the reproduction performance. However, 

whether the individual variation in feed intake, stress and fear in sows group housed under 

commercial conditions is severe enough to impair the reproduction performance is not 

known. Therefore a detailed farm study including 14 herds (in total about 550 sows) with 

different layouts and management routines was carried out, and the relations between various 

indicators of feed intake, stress and fear and reproduction performance were studied. 

11.4 % of all mated sows were re-mated and average litter size was 14.8 born piglets per 

litter. Positive correlations between back fat gain from weaning to three weeks after mating 

and chance of pregnancy (P

- Paper IV - 


Group housing of non-lactating sows is becoming increasingly widespread in commercial 

sow herds in European countries as a result of changed EU-legislations (Council Directive 

2001/88/EC amending Directive 91/630/EEC Laying Down Minimum Standards for the 

Protection of Pigs) and national extraordinary laws (Baustad & Lium, 2002; The welfare of 

Farmed Animals (England) (Amendment) Regulations 2003) initiated by elevated public 

concern of animal welfare. Although no legislation yet, similar tendencies are also seen in 

other parts of the world (Trezona, 2003). 

Impaired reproduction in the shape of reduced litter size or pregnancy rate has been observed 

in group compared to individually housed non-lactating sows in several on-farm 

studies (Hurtgen et al., 1980; Fisker, 1995; Peltoniemi et al., 1999; Hansen, 2000). Conversely, 

in other studies, no difference (England & Spurr, 1969) between grouped and individually 

housed sows or even opposite effects (Bates et al., 2003; Hansen, 2003) have been 

found. The divergent results are probably a result of differences in the function of the group 

housing systems and shows that group housing do not ‘automatically’ lead to poor reproduction 

performance. 

Results from experimental studies, not necessarily reflecting conditions seen in practice 

have indicated that the impaired reproduction performance seen under some circumstances 

in group housed non-lactating sows might be a result of social relations causing individual 

variation in energy intake (review by Kongsted, 2004b), fear and stress (review by Kongsted, 

2004a). 

Further, registrations of various indicators of feed intake, stress and fear in sows group 

housed under various on-farm conditions suggest a large individual variation in these characteristics 

(Kongsted et al., 2004). However, whether these individual variations are severe 

enough to impair the reproduction performance in sows group housed in commercial herds 

is not known. Therefore, a detailed farm study including 14 commercial sow herds with 

different layout and management routines was carried out to investigate the relation between 

various indicators of feed intake, stress and fear and the reproduction performance in 

practice. 

2. Materials and methods 

2.1 Design and herds 

In 14 herds with group housed non-lactating sows, ten focal sows (F-sows) in each of four 

batches were observed from weaning to farrowing. The ten sows were randomly chosen in 

the lactation unit just before the sows were moved to the service unit. The F-sows’ back fat, 

89

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eating and lying behaviour, skin lesions and reaction in fear test were monitored at wean- 

ing, at mating and/or three weeks after mating. 

The study was conducted during an 11-month period from May 2003 to March 2004. The 

timing of the registrations differed maximum 1.5 months between the herds. The 14 herds 

were chosen to represent different layouts and management routines to ensure that any 

found correlations could be transferred to apply in a broad spectrum of herds. The herd 

sizes varied from 180 to 1000 sows. Feeding systems applied in the service unit were freeaccess 

feeding and insemination stalls (11 herds), providing feed in long trough (1 herd), 

floor feeding (1 herd) and biofix (1 herd). Feeding systems applied in the pregnancy unit 

were floor feeding (5 herds), providing feed in long trough (2 herds) or feed dispenser (1), 

Electronic Sow Feeding (2 herds), free-access feeding stalls (2 herds), individual feeding 

stalls (1 herd) and biofix (1 herd). See Kongsted et al. (2004) for a more detailed description 

of the farms. 

2.2 Recordings 

2.2.1 Reproduction and culling data 

For each F-sow, weaning date, date for first mating, date for re-mating for the sows that 

returned to oestrus after the first mating were recorded, farrowing date and the number of 

born piglets (alive and stillborn). A sow was defined as pregnant after first mating if no 

date for re-mating was noted. For culled sows, the date of culling and estimated culling 

reason was recorded. The sows were only followed until re-mating, culling or farrowing. 

Therefore, the number of culled sows did not include any re-mated sows. 

2.2.2 Indicators 

The timing of the recordings of the indicators was first of all chosen to give information 

about the sows’ conditions from weaning to first mating and from first mating to three 

weeks in pregnancy because these stages are believed to be the main periods of relevance 

regarding reproduction performance (Kongsted, 2004ab). The motives for choosing the 

respective indicators are discussed in Kongsted (2004a) and a more thoroughly description 

of the recordings is provided in Kongsted et al. (2004). 

Back fat gain and eating behaviour were used as indicators for feed intake. Back fat depth 

was measured by means of a digital ultrasound back fat indicator LEAN MEATER ® (Baltic 

Korn A/S, Naestved, Denmark) 65 mm from either side of the backbone at the 12 th (last) 

and 10 th rib (conventionally known as P2-measurements) at weaning and three weeks after 

mating. Eating behaviour was only registered in the eight herds with group feeding in the 

pregnancy unit. For each sow, it was recorded whether the sow was eating or not for each 

half minute during feeding three weeks after mating. Number of times the sow was not eat- 

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ing compared to number of recordings (max 50) was calculated for each sow (% not eating). 

Three fear tests were performed as indicators of fear. One Human Approach test (HA-test) 

were performed when sows were routinely moved at weaning (Rousing et al., 1999; Bonde 

et al., 2003). The sow had to pass a human (research technician) at a passage of 10 metres 

long and about one meter wide. The human was placed halfway. If the relation between the 

time required to approach the person compared to the total time required to pass the 10 metres 

were more than 0.67 then the sow was categorised as fearful. Two Forced Human Approach 

tests (FHA-tests) were performed in the home arena of the sows (Andersen et al., 

2003, Pedersen et al., 2003) three weeks after mating. The sows’ reaction was categorised 

into reaction 1 to 6 and 1 to 3 respectively with low score indicating fleeing behaviour. 

Only sows, which scored 1 or 2 in the first and 1 in the second test, were categorised as 

fearful. 

Involvements in aggressive interactions, skin lesions and lying behaviour during resting 

periods were used as indicators of stress. The total number of aggressive interactions the 

individual sow participated in together with the number of lost interactions the first hour 

after weaning was recorded. The total number of skin lesions on head, ears, neck and 

shoulders were recorded for each sow at mating and three weeks after. Every five minute 

during resting period at weaning and three weeks after mating for 25 minutes, it was registered 

whether the sow was lying solitary (defined as lying/sitting in a distance of 20 cm or 

more from other sows) or socially. If the sow was lying alone more frequently than socially, 

the sow was categorised as lying solitary. 

2.4 Statistical analysis 

When analysing the effect of the indicators on the interval from weaning to first mating, 

pregnancy chance, culling risk and litter size, the following model was applied: 

E(Yijk)= µ+αI(ijk)+γI(ijk) W +γI(ijk) AM +δI(ijk) W +δI(ijk) AM + Ai + Bi(j)+ 

91 

7 

∑ 

u=1 

βu xuijk 

Where Yijk is the observation for herd i, batch j and sow k. αI(ijk) is the effect of parity group 

I(ijk) (1, 2-3 and >3 parity). I(ijk) is an indicator function given the parity of observation 

ijk. The indicator functions are specific to each effect, however, to keep Eq. (1) as simple as 

possible this I() notation is used throughout. γI(ijk) W and γI(ijk) AM is the effect of fear category 

(j,k =fearful, confident) at weaning and three weeks after mating respectively, δI(ijk) W and 

δI(ijk) AM the effect of lying behaviour (l,m=lying solitary, lying socially) at weaning and 

(1)

- Paper IV - 

three weeks after mating respectively. Ai and Bi(j) are the normal distributed random effects 

of herd and batch nested within herd. 

All covariates are represented in the last expression in Eq. (1). x1-7ijk is 1. the lactation 

length transformed by the natural logarithm, 2. the back fat at weaning, 3. the back fat gain 

(mm/week), 4. and 5. the number of skin lesions at mating and three weeks after mating 

transformed by the natural logarithm, 6. the number of aggressions and 7. % not eating 

transformed by square root respectively. β1-7 are regression parameters. 

The interactions between parity group and the indicators were also included in the model 

one by one but for the sake of simplicity these are not included in Eq. (1). 

For pregnancy chance after first mating and culling risk, E(Yijk) corresponds to logit to the 

probability of the observed outcome, pijk. For the interval from weaning to first mating and 

litter size, Yijk ~ N(E(Yijk), σijk 2 ) whereas for pregnancy chance and culling risk, Yijk ~ B(1, 

pijk). 

Some exceptions were made to the general modelling strategy. The model for effect on litter 

size and pregnancy chance included the additional covariate, weaning to first mating 

interval. Similarly, when analysing interval from weaning to first mating, sows mated later 

than eight days after weaning (26 sows) were excluded from the analysis, and only covariates 

measured at weaning and mating were included in the model. In an experimental study, 

sows with back fat less than 10 mm were more predisposed to culling compared to fatter 

sows (Young et al. 1990). Therefore, when analysing risk of culling the analysis was repeated 

with the continuous covariate back fat at weaning categorised into a discrete variable 

with two levels: back fat category (

- Paper IV - 

mixed model using the glmmPQL function in the MASS package (Venables & Ripley, 

2002) of R (R Development Core Team, 2004). 

3. Results 

For the reproduction parameters, the overall averages and the variation between sows 

across all 14 herds are presented in Table 1. In average, the sows involved in this study 

showed a very high litter size of nearly 15 born piglets per litter. The percent of re-mated 

sows varied from 0 to 45% and the number of born piglets per litter varied from 13.6 to 

15.7 between the herds. 

Table 1. Overall level and variation in different production parameters for all focal sows 

N Mean Std Min Max 

Interval from weaning to first mating, days 541 5.3 - 2 40 

Re-mated sows, % 541 11 - - - 

Culled in all, % of weaned 554 4.4 1) - - - 

Total number of born piglets/litter 2) 437 14.8 3.3 4.0 24.0 

Number of dead born/litter 437 1.5 - 0 12 

1) Any sows culled after re-mating are not included 2) Alive and dead born 

Parameter estimates and standard errors from the analysis of weaning to first mating interval, 

pregnancy chance and litter size are shown in Table 2. There were no effects of % not 

eating, aggressions after mixing, fear or lying behavior for any of the dependent variables. 

Weaning to first mating interval. The total number of skin lesions at mating tended to correlate 

positive with weaning to first mating interval (P=0.07) and a significant two-factor interaction 

between back fat at weaning and parity was found, in that the interval decreased 

with increased back fat at weaning but only for first parity sows (Figure 1). Further, a significant 

negative correlation with lactation length was found. No main effects or interactions 

with parity for aggressions, fear category or lying behaviour were found. 

93

Days from weaning to first mating 

5,2 

5 

4,8 

4,6 

4,4 

4,2 

4 

3,8 

3,6 

3,4 

parity 1 

parity 2-3 

parity >3 

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 

Back fat at weaning, mm 

Figure 1. The modelled relation between back fat at 

weaning and days from weaning to first mating for 

each parity group (P

Table 2. Estimates and standard error for all independent variables when analysing the effect on interval from weaning to first mating, pregnancy chance 

and litter size 

N Range 1) Weaning to first mating interval Pregnancy chance Litter size 

Estimate Std.err. P-value Estimate Std.err. P-value Estimate Std.err. P-value 

Intercept 5.43 0.45 10.24 3.29 6.96 3.28 

Parity 554 0.0002 0.006 

1 0.66 3) 0.23 0 . -0.73 0.42 

2-3 -0.02 3) 0.18 0.98 0.32 0.50 0.36 

>3 0 3) . 1.15 0.39 0 . 

Lactation length, ln(days) 554 -0.30 0.13 0.02 -1.21 0.72 0.24 2.30 0.74 0.003 

Weaning to first mating int., days 515 0-8 -1.11 0.31 0.0004 -0.22 0.26 0.39 

Back fat at weaning, mm 551 6-35 0.01 3) Indicators 

0.01 0.03 0.06 0.03 0.43 0.07 0.04 0.11 

Back fat gain, mm/week 481 -1.3-1.9 0.67 0.29 0.02 0.59 0.33 0.08 

Not eating AM 2) , square root(%) 299 0-100 - - NS - - NS 

Skin lesions M 2) , ln(no.) 542 0-171 0.04 0.02 0.07 - - NS - - NS 

Skin lesions AM 2) , ln(no.) 543 0-208 - - NS - - NS 

Aggressions, square root(no.) 552 0-66 - - NS - - NS - - NS 

Fear (HA-test) W 2) 513 - - NS - - NS - - NS 

Fear (FHA-test) AM 2) 529 - - NS - - NS 

Lying behaviour W 2) 253 - - NS - - NS - - NS 

Lying behaviour AM 2) 1) 

Untransformed values 

386 - - NS - - NS 

2) 

W: at weaning, M: At mating, AM: three weeks after mating 

3) 

Parity group interacted with back fat at weaning, estimate for interaction for parity group one, two and three respectively: -0,041 (0,016), -0,0019 (0,011), 0

- Paper IV - 

4. Discussion 

The average litter size was high compared to earlier studies, whereas the percentage of 

sows re-mated corresponded to several previous on-farm studies (Gjein & Larssen, 1995; 

Olsson & Svendsen, 1997; Hansen & Kongsted, 2002). The high litter sizes of the sows 

involved in this study, support that group housing of non-lactating sows does not necessarily 

lead to poor reproduction performance. 

The chance of pregnancy (P=0.02) and number of born piglets per litter (P=0.08) decreased 

with decreased back fat gain from weaning to three weeks after mating. Furthermore, sows 

eating less than 20% of the observations at feeding were in markedly higher risk of returning 

to oestrus compared to sows eating more frequently (P

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cial effect on high ranked sows (equal to the sows receiving fewest aggressions) more than 

a suppressing effect in sows of low rank in respect to weaning to oestrus interval. 

A negative effect of a poor body condition at weaning on weaning to oestrus interval is well 

documented in experimental studies (reviews by Dourmad et al., 1994; Whittemore, 1996). 

In this study, however, this effect was seen only in first parity sows. This indicates that first 

parity sows are more sensitive to a low back fat at weaning compared to older sows as also 

proposed by Whittemore & Morgan (1990). These results show that if it is difficult to avoid 

poor body condition at weaning, special attention should be given in the post weaning period 

to young sows. The negative effect of a low back fat depth at weaning might be caused 

by reduced LH level (Aherne & Kirkwood, 1985). Since boar stimuli after weaning may 

stimulate LH secretion in sows with metabolic constraints (Langendijk, 2001), careful boar 

stimulation could perhaps counterbalance the negative effect of poor body condition at 

weaning. 

In agreement with a previously experimental study (Young et al., 1990), a relation between 

back fat depth and culling was found, in that sows with a very low back fat depth at weaning 

(less than 10 mm) were more likely to be culled later in the non-lactating period compared 

to sows with 10 mm or more back fat (P

- Paper IV - 

hour after mixing (Kongsted et al., 2004). However, sows involved in many aggressions at 

weaning had the fewest skin lesions three weeks after mating (Kongsted et al., 2004). As a 

consequence, any stress experienced by these old, and probably high ranked sows (Arey & 

Edwards, 1998) might have been too short lasting to influence their reproduction. The 

number of skin lesions has previously shown to correlate with incidences of aggressive acts 

(Barnett et al., 1992). However, not only physical contact but also treats and visual contact 

may cause stress in the submissive sows (Ruis et al., 2002). Skin lesions per se may there- 

fore be inadequate to determine levels of stress. Finally, the lack of relation between repro- 

duction and fear could partly be due to the timing of the fear tests. Fearfulness towards hu- 

mans around oestrus might decrease the chance of a correct timing of ovulation and in- 

semination (Kongsted, 2004a). However, the fear tests were not performed on the observation 

day around mating because the oestrus behaviour of the sows made the test results unreliable 

(Kongsted et al., 2004). Therefore, the fear tests were only carried out at weaning 

and three weeks after mating, and it cannot be excluded that the fearfulness of the sows at 

that time were different compared to around mating. 

In conclusion, with the heterogeneity of the herds involved and the non-standardisation of 

possible influential factors related to layout and management in mente, the found relations 

are noteworthy. Taken together, the results indicate that the individual variation in feed 

intake in sows group housed in commercial herds may be large enough to impair pregnancy 

rate and perhaps also litter size. However, it cannot be excluded that the found associations 

between back fat and reproduction are linked to social stress. The relations between indicators 

of feed intake and reproduction performance may not only be a consequence of feed 

intake per se but a combination of low feed intake and a high level of social stress in the 

low ranked sows. Additional studies are needed to illuminate the role of social stress in 

commercial sow herds further. Special attention should be aimed at developing additional 

indicators of social stress suitable for use in practical pig production. 

Acknowledgements 

The author wishes to thank the participating farmers and the technicians Henrik K. Andersen, 

Kristine R. Hansen, Michael Hansen, Orla Nielsen, Niels H. Thomsen, and Helge Yde 

for their much appreciated assistance in carrying out the data collection. The author also 

wishes to express her gratitude to John E. Hermansen and Troels Kristensen for valuable 

comments on this paper and to Erik Jørgensen for valuable contributions to the statistical 

analyses. 

98

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101

102

- General discussion - 

GENERAL DISCUSSION 

The specific aims of this thesis were 1) to identify important causes for impaired reproduction 

performance in group housed sows and 2) to define and evaluate indicators suitable for 

use in decision-making to improve the reproduction performance of commercial herds with 

group housed sows. 

Based upon a review study, the hypotheses put forward were: 1) individual variation in energy 

intake as well as fear and social stress might be important causes for impaired reproduction 

performance in group housed non-lactating sows, and 2) back fat, skin lesions and 

behavioural measurements might be indicators of these characteristics, suitable to express 

variation in sows’ reproduction performance under practical conditions. 

The results of the detailed farm study, including 14 commercial herds, supported that group 

housing may lead to individual variation in feed intake severe enough to impair pregnancy 

rate and perhaps also litter size (Paper IV). The 14 herds were chosen to represent different 

layouts and management routines to ensure that any relation found could be transferred to a 

broad spectrum of herds. For the 554 sows followed, a significantly (P=0.02), positive correlation 

between back fat gain and chance of pregnancy was found and further a tendency 

(P=0.08) to a positive correlation between back fat gain and litter size. The modelled relations 

indicate that a sow with a negative back fat gain of 0.5 mm per week has 5 percentage 

points lower chance of pregnancy after first mating and 0.6 fewer born piglets per litter 

compared to a sow with a positive back fat gain of 0.5 mm per week. In addition, it was 

found that sows eating less than 20% of all observations three weeks after mating had a 

significantly (P


No convincing associations were found between the indicators of stress and fear and the 

risk of returning to oestrus or litter size. As some of these indicators, though not pro- 

nounced, was significantly related to back fat gain, e.g. number of skin lesions (Paper III), 

the reason could be that including back fat in the statistical model left little variation to be 

explained by the other indicators. However, even after exclusion of back fat gain, no sig- 

nificant effects were found on any of the indicators of stress. This does not necessarily 

demonstrate that no relations between reproduction and these characteristics exist. As dis- 

cussed in Paper IV, it cannot be excluded that the indicators applied have been insufficient 

to express variation in levels of social stress. Special attention should be paid to developing 

additional indicators of social stress suitable for use in commercial sow herds. In this study, 

all the indicators of social stress were related to aggressive interactions (e.g. direct behav- 

ioural observations of aggressions and the number of skin lesions). However, not only 

physical contact but also treats and visual contact may cause stress in the low ranking sows 

(Ruis et al., 2002), and sows receiving many aggressions are not necessarily identical with 

the most submissive sows, as shown and discussed in paper III. Therefore, in any complementary 

future study, efforts should be made to estimate the rank (high, medium, low) of 

the individual, focal sow. As already discussed, in group feeding systems, sows with limited 

access to the feed are probably identical to the most submissive sows. However, in systems 

with individual feeding, access to feed cannot necessarily be used as an indicator of 

rank. In these systems it might be possible to estimate rank by provoking a competition 

situation e.g. by providing a small amount of feed in the corner of the pen. 

As presented in Paper II, human approach tests were used as indicators of fear, because it 

was hypothesized that submissive sows would react fearfully towards humans due to their 

negative experience during grouping. However, this has never been verified and some of 

the research technicians actually had the impression that the most submissive sows were the 

ones that reacted most confidently towards humans. This indicates that human approach 

tests cannot be used for assessing the rank of the sows. This is further supported by the lack 

of associations between parity group and the outcome of the two fear tests performed after 

grouping of the sows (paper III). 

The results from the farm study indicated that back fat measurements and observations of 

sows’ eating behaviour might be relevant indicators of reproduction problems since 1) they 

were possible to perform in sows group housed under practical conditions and 2) a relation 

was found between reproduction performance and these characteristics. Consequently, 

these indicators might be relevant ingredients of a management tool to analyse and improve 

the reproduction performance of group housed non-lactating sows. 

104


However, an indicator is not necessarily well suited in an operational context just because 

the indicator is possible to perform in commercial herds and well related to the phenomena 

under study. Indicators applicable in a management tool should further be meaningful for 

the individual farmer (Halberg, 1996). It is e.g. important that the individual manager be- 

lieves that an indicator provides useful and relevant information, because otherwise he/she 

will not be motivated to use this as a management tool. Furthermore, it is essential that an 

indicator is possible to measure or register by farmers or advisors within reasonable time 

and costs (Halberg, 1996; Rousing et al., 2001; Sørensen et al., 2001). Whether the two 

indicators mentioned above meet these requirements will be discussed in the following. 

A systematic investigation of whether the indicators applied were perceived as meaningful 

by the farmers, e.g. by means of qualitative interviews (Vaarst, 2003) has not been carried 

out. However, none of the farmers or managers questioned the relevance and usability of 

the back fat measurements or the observations of eating behaviour at the introductive farm 

visits or during the recordings. 

Observation of eating behaviour. Time has become a very important issue in pig management, 

as the average labour input per animal has decreased (Madsen, 2001; Rasmussen, 

2003). The time necessary to observe sows’ eating behaviour was 10 to 25 minutes per 

batch as one group of sows were observed per batch and the recordings were carried out 

until the last sow had stopped eating or at longest 25 minutes after feeding start. Following 

four batches would then acquire between 40 m and 1.7 h plus the time required to select 

and mark ten random, focal sows. This seems as a feasible time range in most herds. However, 

the disadvantage of manually recording the eating behaviour is that a maximum of ten 

focal sows can be overviewed at a time. As a consequence hereof, there is a risk that an 

existing problem will not be detected. This problem could, however, be overcome if the 

identification of sows with a low feed intake could be automated. O'Connell et al. (2003) 

report that low ranking sows visit the drinker more often than the high ranking in a group of 

sows and according to own observations it seemed that sows with a very low feed intake 

often visited the drinker during feeding. Online registration of pigs’ drinking pattern as an 

indicator of e.g. an outbreak of diarrhoea has already been implemented as a commercial 

software package, Farm Watch® (Madsen, 2001). Likewise, it might be possible to detect a 

feed-related problem in submissive sows by automatical registration of the water consumption 

during feeding. In that case, it would probably be possible to identify and pay special 

attention to ‘problem sows’ before the reproduction performance was influenced negatively. 

Back fat measurements. Assessment of back fat gain from weaning to three weeks after 

mating cannot be used for identifying individual sows with a potential reproduction prob- 

105


lem, because three weeks after mating their reproduction will already have been impaired. 

However, assessment of back fat gain can provide the farm manager with valuable indica- 

tions of whether variation in back fat gain, in general, could be a contributing reason for 

impaired reproduction in group housed sows. The time necessary for back fat measurements 

was not recorded in this farm study. However, the back fat measurements were estimated 

to be possible to perform within two or three minutes per sow including finding the 

measuring points, shaving and measuring. A recent Danish test trial showed that back fat 

measurements with a similar digital ultrasound back fat indicator, in average requested approximately 

one minute per sow if the measuring points were marked and the sows were 

shaved in advance (Thorup, 2004 pers. comm.). This, in combination with a low price 

(DKK 4,800 ~ EUR 650) makes LEAN-MEATER® a potential management tool. However, 

the suitability of the equipment has recently been questioned due to a large withinobserver 

variation, which makes it inappropriate for use at individual sow-level (Thorup, 

pers. comm.). More accurate two-dimensional back fat indicators are available on the market. 

As some of these can be used for pregnancy diagnosis too, they will perhaps be potential 

management tools in spite of the considerable larger price. 

The 14 herds involved in the farm study differed markedly with respect to the reproduction 

performance of the approximately 40 sows observed per herd. Return percentage varied 

from 0 to 45% with an average of 11% and litter size differed from 13.6 to 15.7 with an 

average of 14.8 total born piglets per litter. These figures support the assumption that group 

housing of non-lactating sows does not ‘automatically’ lead to poor reproduction performance 

and further that it will be possible to improve the reproduction performance in some 

commercial herds. 

Improving the reproduction performances is, however, not the only challenge that managers 

of group housed sows are facing. Group housing was implemented with the aim to improve 

the animal welfare in commercial pig production. However, submissive sows eating in less 

than 20% of all observations during feeding because they are kept away from the feed, 

sows having less than 10 mm back fat at farrowing and sows with more than 150 skin lesions 

at the end of the gestation, as found in the present farm study are not equal to animal 

welfare. Therefore, efforts should be made to improve not only the reproduction performance 

but also the animal welfare in group housed sows. 

106

References 





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Husdyrbrugsforsøg. 

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sity, Copenhagen. 

Mendl, M., Zanella, A.J., Broom, D.M., 1992. Physiological and reproductive correlates of behavioural stra- 

tegies in female domestic pigs. Animal Behaviour 44, 1107-1121. 

O'Connell, N.E., Beattie, V.E., Moss, B.W., 2003. Influence of social status on the welfare of sows in static 

and dynamic groups. Animal Welfare 12, 239-249. 



Rasmussen, J.D.L.K., 2003. Erfaringer med tidsforbrug i drægtighedsstalde. Erfaring 301, Den rullende Af- 

prøvning, Landsudvalget for Svin, Danske Slagterier, 11pp. 

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53-57. 


coping characteristics and social status for welfare and production of paired growing gilts. Appl. 

Anim. Behav. Sci. 75, 207-231. 

Sørensen, J.T., Sandøe, P., Halberg, N., 2001. Animal welfare as one among several values to be considered 

at farm level: The idea of an ethical account for livestock farming. Acta Agric. Scand. , Sect. A, 

Animal Science Suppl. 30, 11-16. 

Thorup, F. 2004. Ph.D. The National Committee for Pig Production, Danish Bacon and Meat Council. Per- 

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qualitative interviews. Animal Welfare 12, 541-546. 

107

108

- Conclusions - 

6. CONCLUSIONS 

Two review papers revealed a good theoretical and experimental background for believing 

that individual variations in feed intake, social stress and fear could be contributing reasons 

for impaired reproduction seen in some group housed sows. The results of a detailed farm 

study including 14 commercial herds, supported the assumption that group housing in practice 

may lead to individual variation in feed intake severe enough to impair pregnancy rate 

and perhaps also litter size, as correlations between back fat gain and reproduction performance 

as well as between eating time and reproduction performance were found. As a 

consequence hereof, back fat measurements and observations of the eating behaviour of the 

sows might be useful components in a decision-support tool to analyse and improve the 

reproduction performance in group housed sows. No convincing correlations were found 

between chance of pregnancy and litter size on one side and the indicators of social stress 

and fear on the other. Since stress and fear are difficult to measure, this does not necessarily 

demonstrate that no relations exist between reproduction and these characteristics. It does, 

however, indicate that the indicators applied are unsuitable to reflect the reproduction performance 

of group housed sows under practical conditions. 

109

110

- Appendix 1 - 

APPENDIX 1 

LITTER SIZE AND FARROWING RATE, WHICH PHYSIOLOGICAL PROCESSES 

MAY GO WRONG AND WHY? 

Successful reproduction, characterized by establishment and maintenance of pregnancy and 

a high litter size, depend on a series of precisely timed physiological and endocrine events 

in the period from weaning to farrowing. Some of these events are illustrated in Figure 1 

and will be explained in the following text. 

Day 117 

Day 13-25 

Posterior pituitary gland Anterior pituitary gland Developing follicles Uterus Corpus Luteum 

Oxytocin 

Maintenance of pregnancy 

Implantation of ova in the 

uterus 

+ fertilisation 

Farrowing 

The mature ova pass 

down into the uterus 

Day 3.5 

FSH LH Oestrogen Prostaglandin Progesteron 

Weaning 

÷ fertilisation 

Regression of 

corpus luteum 

The ruptured follicles 

form corpus luteum 

Release of the mature ova 

(=ovulation) 

The physiological events will be discussed in events happening 1) before and around mating/insemination 

and 2) after mating/insemination. After that the endocrine control of the 

physiological events will be presented. Finally, a short discussion of which parameters may 

influence these events will be carried out. 

111 

Development and maturation 

of ovarian follicles 

Day 1 

Mating/insemination 

Transport of semen 

Oestrus behaviour 

Figure 1. Reproduction related physiological and endocrine events in the period from weaning to 

farrowing (see text for further explanation) 

Day 0


Physiological events before and around mating/insemination 

To gain pregnancy and a high litter size, onset of oestrus has to appear followed by ovulation, 

the number of ovulated eggs have to be high and further, the artificial insemination or 

mating has to bee successful resulting in fertilisation and a high number of fertilised eggs. 

At luteolysis (around day 16 in oestrus cycle when the luteal phase is replaced by the follicular 

phase) or at weaning, 15-25 follicles are recruited and selected to undergo preovulatory 

growth and to ovulate 4-7 days later (Prunier & Quesnel, 2000b). A few days after 

weaning the sow start to show oestrus. The interval from weaning to onset of estrus (WEI) 

and duration of estrus varies to a large degree between farms and also between sows within 

farms (see Table 1). 

Table 1. Examples of interval from weaning to onset of estrus (WEI) and duration of estrus (ED) reported 

in the literature 

WEI, hours after weaning ED, hours 

X, +/-SD Range X, +/-SD Range 

Pedersen & Navntoft, 1996 112+/-11 - 49+/-7 - 

Pedersen & Navntoft, 1996 100+/-17 - 61+/-10 - 

Nissen et al., 1997 92+/-13 64-134 60+/-14 30-89 

The interval from onset of estrus to ovulation is reported to be in the range of 10 to 85 

hours for individual sows, with mean values of 15 to 35 hours (review by Kemp & Soede, 

1997). The duration of estrus and the interval from onset of oestrus to ovulation is negative 

correlated to WEI (Nissen et al., 1997). The duration of ovulation ranges from one to three 

hours (Kemp & Soede, 1997). At ovulation the released ova are expelled into the oviduct 

and transported to the ampullary-isthmic junction, the site of fertilisation, perhaps in 30-45 

min or less (Hunter, 1990). At insemination or mating sperm cells are deposited at the 

utero-cervical junction. Sperm cells migrate through the uterine horns to the oviducts where 

they are temporarily stored in the sperm reservoir near the utero-tubal junction (Hunter, 

1990). This transport is believed to be dependent mainly upon uterine contractions (Scott, 

2000). Hunter (1981) found that within 1-2 h after mating there were enough spermatozoa 

in the oviduct to promote 100% fertilisation. Before the sperm are capable of fertilisation 

they have to undergo capacitation (maturation), which is presumed to happen in the sperm 

reservoir (Rodriguez-Martinez et al., 2001). Capacitation is believed to require five to six 

hours but can be accelerated to less than two hours if insemination is performed around 

ovulation (Hunter, 1990). By the time ovulation approaches, sperm are released from the 

reservoir to the oviduct (Hunter, 1981). 

The ova are only capable of being fertilised the first eight hours after ovulation (Hunter, 

1967) and the sperm needs to be present in the female tract for about two h or longer before 

112


they are mature i.e. capable of fertilisation (see above). The fertilisation ability of the sperm 

in the female tract begins to decline after 12 hours (Dziuk, 1970) but can survive for more 

than 44 h (Kemp & Soede, 1997). Therefore a successful insemination or mating also de- 

pends upon clear oestrus behaviour of the sow and a co-ordination between oestrus behav- 

iour and ovulation, which as will be discussed later, depends on a good hormonal function. 

Physiological events after mating/insemination 

To gain pregnancy and a high litter size, the embryo survival also has to be high. A high 

embryo survival depends upon whether the following events are successful. 

Fertilised eggs are moving from the ampullary-isthmic junction (where fertilisation occurs) 

to the uterus. During this journey, which takes about 48 h, the eggs under go cleavage (cell 

division) and when they reach the uterus, they are at the four-cell stage (Dziuk, 1985; 

Ashworth, 1991). In the uterus the cell divisions continue (Hughes et al., 1996). On day six 

to day seven hatching from the zona pellucida (which is a complex glycoprotein matrix 

formed around each oocyte during follicular development (Dunbar & Bundman, 2003) occurs 

(Stroband & Lende, 1990). After hatching, the eggs become increasingly dependent 

upon nutrients in uterine secretions (Ashworth, 1991). Between day 7 and 12 of pregnancy 

the fertilised eggs redistribute themselves over the full length of both uterus horns (Dziuk, 

1985). Finally the elongation and the implantation (attachment to the uterine endometrium) 

take place. Elongation starts around day 10 of gestation (Ashworth, 1991; Geisert & Yelich, 

1997). During elongation the embryos undergo a morphological change from 10 mm 

spherical (i.e. round) to tubular (20-40 mm) and finally filamentous (up to 100 cm in 

length!) shapes by day 14-16 (Ashworth, 1991; van der Lende et al., 1994; Geisert & Yelich, 

1997). The implantation starts around day 13-14 of pregnancy and is completed about 

24 days after fertilisation (Crombie, 1970; Ashworth, 1991). Each embryo is surrounded by 

separate fluid filled membranes, the amnion and chorion, which form the placenta 

(Ashworth, 1991). From day 18 to day 30 of pregnancy the volume of this fluid increases 

markedly (Ashworth, 1991) and it is the presence or absence of this fluid that can be detected 

by the commonly used ultrasound pregnancy diagnosis instruments. On day 35 of 

pregnancy the embryo is approximately four cm long (van der Lende, 1989) (see Figure 2). 

113


Figure 2. A pig embryo approximately 30 days old (Maddox-Hyttel, 2003) 

The major part of prenatal mortality occurs in the first 35 days of pregnancy and perhaps 

especially before day 18 of pregnancy (Pope & First, 1985; van der Lende et al., 1994). The 

average embryo mortality is in the range of 20-30 % but with large variation between and 

within populations (van der Lende et al., 1994). The last mentioned is illustrated in a study 

by van der Lende (1989) where the embryo mortality varied from 0 to 67 % in 71 gilts. 

Hormonal control of reproduction 

The above-mentioned physiological events are under sharp endocrine control of the hypothalamo-piturity-ovarian 

axis (Turner et al., 2002). Gonadotrophin-releasing hormone 

(GnRH) is released from the hypothalamus and transported to the anterior pituitary gland 

where it stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone 

(FSH). Luteinizing hormone and FSH act on the ovaries to stimulate the development 

of the pre-ovulatory follicle (Foxcroft & Hunter, 1985). FSH is necessary to support follicular 

growth up to 5-6mm whereas LH is necessary for the final stages of follicle maturation 

(Britt et al., 1985). These developing follicles produce oestrogen, which is the primary 

trigger of oestrus behaviour (Hughes et al., 1996). The increased level of oestrogen influences 

the hypothalamus to increase the secretion of LH. The LH peak introduces changes in 

the follicle wall eventually leading to ovulation (Hughes et al., 1996). 

The ratio of oestrogen and progesterone and the level of prostaglandin influence the transport 

of the released ova to the site of fertilisation by causing contractions of the oviduct 

(Frandson & Spurgeon, 1992). Oestrogen and prostaglandin increase uterine activity and 

progesterone decreases uterine activity (Langendijk, 2001). Prostaglandin is also involved 

in the transport of semen from the uterus to the site of fertilisation (Soede, 1993). This 

transport is furthermore depending on small amounts of oxytocin, released from the posterior 

gland at the onset of oestrus, causing strong contractions of the uterus (Hughes & Varley, 

1980). The oxytocin release is augmented by both external (the presence of a boar) and 

internal stimulation (from seminal oestrogens) (Soede, 1993). 

114


Soon after ovulation the granulosa cells lining the follicle wall begins to multiply to form a 

corpus luteum (CL) (Anderson, 2000). If fertilisation does not occur, prostaglandin pro- 

duced by the uterus is transferred to the ovary were it induces regression of CL. Corpus 

Luteum is essential for maintenance of pregnancy because CL is the only source of proges- 

terone in the sow and progesterone is essential during the whole period of pregnancy (van 

der Lende, 1989). The main function of CL is the secretion of progesterone. Progesterone 

stimulates uterine secretions (among other things IGF-1) and progesterone is the primary 

director of uterine development and secretion (Geisert & Yelich, 1997). Furthermore pro- 

gesterone is necessary to prevent contractions of the uterus, which would be caused by ele- 

vated levels of oestrogen (Hughes et al., 1996). Both oestrogen (Stroband & Lende, 1990) 

and progesterone are involved in preparing the uterine wall for the attachment of the em- 

bryos (Hughes & Varley, 1980). There are indications that LH is essential for maintenance 

of the CL beyond the first 12 days of pregnancy but that this requirement for LH decreases 

after day 29 of pregnancy (Peltoniemi et al., 1995; Hughes et al., 1996). To avoid regres- 

sion of CL at day 16 in oestrus cycle the embryo around day 11-12 secretes oestrogen 

(Bazer et al., 1982; Geisert & Yelich, 1997). This is also called ‘the embryonic signal’ 

(Peltoniemi et al., 2000) or ‘the maternal recognition signal’ (Geisert et al., 1987). Accord- 

ing to Bazer et al. (1982;1984) oestrogen produced by the embryo directs the prostaglandin 

synthesised in the uterus into the uterine lumen which prevent their release to the uterine 

vascular bed and therefore prevents the regression of CL. Oxytocin (Geisert & Yelich, 

1997), which secretion from the endometrium is stimulated by oestrogen, and prolactin 

(Gross et al., 1990 cf Geisert et al., 1994) may also play a role in this redirection of pros- 

taglandin. Bazer et al. (1984) suggested that prostaglandin is only luteolytic on day 12 or 

later after onset of oestrus. However, Estill et al. (1993) found that repeated treatment with 

prostaglandin from day five to day ten also resulted in luteolysis. Geisert et al. (1994) hy- 

pothesise that, before the first embryonic signal, progesterone controls the release of pros- 

taglandin. It seems that a second prolonged embryonic oestrogen signal is required after 

day 14 to maintain pregnancy beyond day 30 (Geisert et al., 1987). 

At the time of parturition foetal cortisol stimulate the prostaglandin production in the 

uterus, which causes regression of the CL followed by a drop in progesterone level (Hughes 

et al., 1996; Anderson, 2000). 

Discussion 

The above-mentioned emphasize that a successful reproduction depends upon a series of 

precisely timed physiological and endocrine events. These events may be disturbed by 

various factors. There are thus indications that the endocrine regulation may be disturbed 

by e.g. stress, as indicated by increased cortisol. In several studies, administration of corti- 

115


sol in oestrus cycle impaired the pre-ovulatory oestrogen surge, the preovulatory LH surge 

and the timing between oestrus behaviour and LH surge in female pigs (Turner et al., 

2002). Likewise did administration of AdrenoCorticoTrophic Hormone (ACTH), followed 

by an increase in cortisol in very early pregnancy impede the cleavage rate of the embryos 

(Razdan et al., 2002). 

Furthermore, there are also indications that the endocrine regulation may be influenced by 

energy intake. A positive correlation is believed to exist between the levels of the energy 

related hormones, insulin and IGF-1, and the levels of LH and FSH (Hughes & Pearce, 

1989; Peltoniemi et al., 1995). Finally, there are indications that a high level of feed intake 

may reduce the level of progesterone (Hughes & Pearce, 1989; Foxcroft, 1997). 

It therefore seems that both stress and energy intake may influence the reproduction physiology 

of the sow. These factors might be very much affected by the group housing system. 

In commercial group housing systems, mixing of unfamiliar sows often occur and in a 

number of studies, mixing of unfamiliar sows have lead to a more or less long-lasting elevated 

level of cortisol in plasma (Pedersen et al., 1993; Tsuma et al., 1996; Olsson & 

Svendsen, 1997b). Likewise, there are several indications that group housing may lead to 

individual variation in energy intake between sows (Brouns & Edwards, 1994; Olsson & 

Svendsen, 1997a; Andersen et al., 1999). 

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