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

- Paper I -
1. Introduction
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. 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
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