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

- General discussion -
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.
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