Management and genetic factors affecting fertility in sows.

Contents The purpose of this article is to summarize the current knowledge on genetic and management methods for improving fertility in sows. Fertilization rate, litter size and the interval between weaning and oestrus are traits that can be monitored on farms. These traits are heritable but can also be influenced by management. Age at puberty and the interval between weaning and oestrus are genetically linked (rg = 0.3) and a shorter weaning-to-oestrus interval is related to a longer duration of oestrus. Consequently, selection may be used to simplify detection of oestrus but because of variation in duration of oestrus between lines/breeds, farm-specific insemination strategies are needed. The direct boar effect on fertilization is small, probably due to the superabundance of sperm cells that is available in each dose of semen. Consequently, the use of a large number of sperm cells per dose is the best management tool for avoiding fertilization problems in sows. Health status of the boars, both for artificial insemination and natural mating, is of importance in order to produce a large number of sperm cells/doses of good quality per ejaculate. It is concluded that factors that influence fertility in sows, particularly prior to and during fertilization, are mainly related to oestrus and the optimal timing of insemination. Selection for adequate symptoms of oestrus, together with farm-specific insemination strategies are needed.