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

- 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.
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