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

- Paper IV -
cial effect on high ranked sows (equal to the sows receiving fewest aggressions) more than
a suppressing effect in sows of low rank in respect to weaning to oestrus interval.
A negative effect of a poor body condition at weaning on weaning to oestrus interval is well
documented in experimental studies (reviews by Dourmad et al., 1994; Whittemore, 1996).
In this study, however, this effect was seen only in first parity sows. This indicates that first
parity sows are more sensitive to a low back fat at weaning compared to older sows as also
proposed by Whittemore & Morgan (1990). These results show that if it is difficult to avoid
poor body condition at weaning, special attention should be given in the post weaning period
to young sows. The negative effect of a low back fat depth at weaning might be caused
by reduced LH level (Aherne & Kirkwood, 1985). Since boar stimuli after weaning may
stimulate LH secretion in sows with metabolic constraints (Langendijk, 2001), careful boar
stimulation could perhaps counterbalance the negative effect of poor body condition at
weaning.
In agreement with a previously experimental study (Young et al., 1990), a relation between
back fat depth and culling was found, in that sows with a very low back fat depth at weaning
(less than 10 mm) were more likely to be culled later in the non-lactating period compared
to sows with 10 mm or more back fat (P