A review of the effect of energy intake on pregnancy rate and litter size–discussed in relation to group-housed non-lactating sows

Abstract

The number of group-housed non-lactating sows is increasing rapidly in Europe as a consequence of changed legislation initiated by elevated public concern of animal welfare. Lower litter size and pregnancy rate in group compared to individually housed non-lactating sows have been observed in several on-farm experiments. The overall aim of this paper is to consider whether the variation in energy intake in a group of non-lactating sows can influence variation in litter size and pregnancy rate. A review of existing literature with main emphasis on publications after 1980 was carried out to clarify whether pregnancy rate and litter size may be influenced by energy intake. The studies reviewed indicate that low energy intake compared to high energy intake before mating may impair litter size in gilts and in sows that experienced severe weight loss during lactation. Furthermore, moderate energy intake compared to low energy intake in the first 3 days after mating may reduce litter size in the gilt but not in the sows. Both pregnancy rate and litter size might be influenced by very low energy intake in the first 4 weeks of pregnancy. Based upon studies indicating that low ranking sows may consume considerably less than high ranking sows (e.g., 50–80%) in group-housed systems, it is suggested that the variation in feed intake in a group of restricted fed pregnant female pigs may be large enough to influence pregnancy rate and litter size.