Seasonal influence on estrous activity in sows and gilts.

Seasonal fluctuations in the estrous activity of sows after weaning and of sows and gilts after mating were determined by analysis of breeding records from eight swine herds covering a total of 19 herd-years of data. Of 11,461 sows, 78.4% were in estrus within 7 days after weaning. From July through September, 68.6% of sows returned to estrus within 7 days after weaning, compared with 82.0% during the remaining 9 months of the year. An increase in postweaning anestrus of more than 30 days' duration also occurred during summer months. Seasonal fluctuations in the frequency of postweaning estrus were similar for sows moved from farrowing facilities to environments with or without specialized temperature control features. For sows confined to crates after weaning, the rate of postweaning return to estrus was 10.4% greater than for sows in group-housing systems, but the seasonal pattern in postweaning return to estrus was not altered. Postweaning estrous failure was more obvious in primiparous sows than in multiparous sows, especially during summer and fall. The frequency of delayed return to estrus after infertile mating was 63.7% for matings during the period July through September and 29.7% for the period January through March. It was concluded that postweaning and postservice estrous activities in swine are influenced by season of the year and by parity. Group housing of sows or individual crating of sows, and water sprinkling or evaporative cooling systems in the postweaning breeding area, as used in the herds investigated, appear to be of questionable value in preventing estrous failure during summer and fall months.