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

- Paper III -
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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