Seasonal infertility in pigs.

A retrospective study of a seasonal infertility problem in a large intensive piggery showed that during the periods of infertility there was a significant increase in the numbers of sows returning to oestrus in the periods 22 to 37 and 44 to 53 days after mating. A prospective study showed that the majority of sows affected by the seasonal infertility problem returned to oestrus during the fourth of fifth week after mating. However, some sows did not exhibit a normal behavioural oestrus at this time and so the oestrus was undetected until and sow completed another oestrous cycle accounting for the second period of increased returns at 44 to 53 days. Some sows failed to exhibit behavioural evidence of oestrus at this second to exhibit behavioural evidence of oestrus at this second oestrus and so had very prolonged mating to detectable oestrus intervals.