Seasonal reproductive inefficiency in large pig breeding units in Britain.

The reproductive performance of five large, intensive pig breeding units was monitored over a period of 930 days. During this time three periods of reproductive inefficiency were noted, these mainly involving animals served during the summer months of July and August. Manifestations of this inefficiency were returns of oestrus, abortions and animals reaching 95 days of presumed gestation not-in-pig. It is suggested that ambient temperature stress, a hitherto unidentified arbortifacient factor, and a seasonal tendency towards suboestrus may have been contributory factors.