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Today many sow herds kept in intensive management conditions exhibit a reduced prolificacy in the second litter while former results had shown an improvement of prolificacy with the litter order from the first to the fifth cycle. The data collected since 1976 in experimental farms exhibiting this reduction in prolificacy were analysed using the multivariate analysis to point out the factors affecting this phenomenon. Data concerning 656 sows with at least two cycles were studied. The variables used were the following : weight change of the sow before and during reproduction, prolificacy in first cycle, feeding and reproductive rhythm (age of the gilt at mating 212.4 ± 14.1 ; lactation length 27.06 -!4.44 ; weaning-fertilization interval 6.11 ± 1.78, sows being systematically culled when this interval exceeded 14 days). Among these factors, prolificacy in first cycle (r = 0.569) was the most involved in the variation of the decrease in prolificacy (32.3 p. 100). It was the same for the prolificacy in second cycle, but its effect was positive (r = 0.187). The following factor was the farrowing-mating interval whose lengthening by 10 days improved prolificacy in second cycle by 0.95 piglet. The lactation length and mainly the weaning-fertilization interval had a significant and favourable effect on the prolificacy in second cycle. They did not totally account for the variation in the decrease of prolificacy, but allowed to relate the recent appearance of this phenomenon to the acceleration of reproductive rhythms. The weight variable accounting the best for the effect of the prolificacy in first cycle was the weight loss during lactation. It was not demonstrated any important and significant effect for the dietary factors and the other variables of the weight change.

Decrease in sow prolificacy at the second litter : analysis of data from two experimental herds