Social behaviour of domestic animals VII. Variation in weaning weight in pigs

SUMMARY Regression analyses were made of the inter-relations among weights at day-old, 3 and 8 weeks, teat order, social order and litter size in 41 litters of young pigs. Birth weight and teat order accounted for 40 % of the variation of 3-week weight within litters. Social rank was strongly influenced by 3-week weight, but not by birth weight or teat order except through their effects on 3-week weight. About 70% of the within-litter variation in 8-week weight was attributable to 3-week weight and social rank. Of the total variation in 8-week weight about 55 % could be explained in terms of the other variables. The effect of litter size on 8-week weight appeared to differ considerably in the Berkshire and Large White pigs used in this study. On the assumption of a causal sequence in time, the within-litter variation in 8-week weight was partitioned into fractions of 19% due to birth weight, 5 % due to teat order, 29 % due to 3-week weight and 17 % due to social rank.