Summer infertility in pigs: its incidence and characteristics in an Australian commercial piggery

Abstract

The records of five years' production in an 800 sow commercial piggery were examined and the relationships between summer temperatures, returns to service and litter size were considered. When mean daily maximum temperature exceeded 32¦C during the week of service there was an increase in the number of sows failing to hold to service. The number of sows that returned to service 15-25 days after mating remained constant throughout the year, and summer infertility was characterized by an increase in the number of sows that exhibited extended, irregular return-to-service intervals. The litter size of sows that conceived during the period of summer infertility was not significantly different from that of sows conceiving at other times of the year. The data suggest that summer infertility is not due simply to fertilization failure, embryonic mortality or an increased incidence of abortions in sows mated during periods of high temperature. Neither does boar fertility appear to be in question. It seems most likely that heat stress around the time of mating may affect ovarian function, resulting in temporary infertility and an endocrine imbalance, which causes delayed, irregular returns to oestrus.