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

- Paper I -
Feeding sows 16, 27 or 37 MJ ME day -1 from day 43 to day 114 in pregnancy did not influ-
ence the litter size (Merk & Kirchgessner, 1984) and in accordance with this, Einarsson &
Rojkittikhun (1993) suggest that feed level of pregnant sows after the first four weeks has
little effect on litter size.
Litter size seems to be unaffected even by low energy supply (e.g. 18.3 MJ ME) during
pregnancy for several parities (Walker, 1983; Whittemore et al., 1984), though, the results
should be treated with caution due to a relative low number of sows per treatment group (23
followed in four gestations, 20 followed in five gestations). However, also in larger scale
studies, no convincing effect of low energy supply for two (Spoolder et al., 1996), four
(Young et al., 1990) or five (Gatel et al., 1987) parities on litter size has been observed. In
some trials, a higher culling rate was seen among the low fed sows (Walker, 1983;
Whittemore et al., 1984; Young et al., 1990) and when the culling reason was reported,
main reasons were reproductive problems like for instance not pregnant and abortions
(Young et al., 1990). In contrast, Gatel et al. (1987) found a slightly higher culling rate for
less restricted fed sows (35.2 MJ ME day -1 ) but this was primarily due to anoestrus after
weaning and leg problems. Locomotion problems are a well-known consequence of high
feed intake during pregnancy (Dourmad et al., 1994). In practice, this could imply consequences
for litter size and pregnancy rate because a higher culling rate will lead to a higher
proportion of first-litter sows in the herd and since younger sows are less prolific than older
sows, this would lead to a reduction in average reproduction performance.
There are several reports of a negative relationship between feed intake during pregnancy
and feed intake in lactation (e.g.Yang et al., 1989; Young et al., 1990; Xue et al., 1997) and
a low feed intake in lactation may reduce ovulation rate and embryo survival (Zak et al.,
1997; Han et al., 2000) and perhaps even conception rate (Hughes et al., 1984) in the next
cyclus. The question is, however, how high feed intake in pregnancy should be before feed
intake in lactation is reduced so much that litter size and conception rate is impaired. In the
above-mentioned long-term trials, the level of feed intake in pregnancy was in the range
from low level (18.3-22.2 MJ ME per day) to moderate level (30.5-38.5 MJ ME per day)
and in these trials, apparently no negative effect of the moderate level of feed intake on
litter size was observed in the subsequent cyclus. However, whether higher feed intake during
pregnancy can influence litter size negatively by reducing feed intake in lactation, is not
possible to conclude based on these studies.
In summary, when looking isolated upon one cyclus, energy supply after the first four
weeks of pregnancy is believed to have little effect on reproduction performance. Regarding
effect of energy intake in several successive pregnancies on reproduction, low energy
intake (21.4 MJ ME day -1 ) for up till five parities does not seem to reduce litter size. However,
low energy intake in several gestations may increase the risk of being culled due to
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