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

- Paper IV -
three weeks after mating respectively. Ai and Bi(j) are the normal distributed random effects
of herd and batch nested within herd.
All covariates are represented in the last expression in Eq. (1). x1-7ijk is 1. the lactation
length transformed by the natural logarithm, 2. the back fat at weaning, 3. the back fat gain
(mm/week), 4. and 5. the number of skin lesions at mating and three weeks after mating
transformed by the natural logarithm, 6. the number of aggressions and 7. % not eating
transformed by square root respectively. β1-7 are regression parameters.
The interactions between parity group and the indicators were also included in the model
one by one but for the sake of simplicity these are not included in Eq. (1).
For pregnancy chance after first mating and culling risk, E(Yijk) corresponds to logit to the
probability of the observed outcome, pijk. For the interval from weaning to first mating and
litter size, Yijk ~ N(E(Yijk), σijk 2 ) whereas for pregnancy chance and culling risk, Yijk ~ B(1,
pijk).
Some exceptions were made to the general modelling strategy. The model for effect on litter
size and pregnancy chance included the additional covariate, weaning to first mating
interval. Similarly, when analysing interval from weaning to first mating, sows mated later
than eight days after weaning (26 sows) were excluded from the analysis, and only covariates
measured at weaning and mating were included in the model. In an experimental study,
sows with back fat less than 10 mm were more predisposed to culling compared to fatter
sows (Young et al. 1990). Therefore, when analysing risk of culling the analysis was repeated
with the continuous covariate back fat at weaning categorised into a discrete variable
with two levels: back fat category (