The seasonal breeding pattern of sows in seven confinement herds.

The breeding herd records from 7 confinement herds were analyzed to determine the association of season with the frequency of estrus within 1 week after weaning and the farrowing rate following mating during this estrus. All herds utilized the cooling of sows during lactation and water fogging during the postweaning, breeding and early gestation periods. During July, August and September, the frequency of estrus within 7 days after weaning was lower (P < 0.05) than the frequency of estrus during October, November and December. The farrowing rate for matings during September and October was lower (P < 0.05) than the farrowing rate for sows mated from February through May. These data suggest that reduced postweaning estrous activity and fertility may occur in confinement herds, despite the use of cooling systems used to minimize heat stress of sows during hot weather.