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

- 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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