Reproductive performance of sows treated with a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin at weaning in the summer.

During the summer and fall of 1987, sows from eight herds in three states were assigned randomly to receive either a combination of 400 IU of pregnant mare's serum gonadotropin with 200 IU of hCG (P.G. 600) or no treatment at weaning. A treatment x parity interaction was observed for days to first estrus after treatment and percentage anestrus (percentage of sows not achieving estrus within 10 d after weaning). Relative to primiparous control sows, primiparous sows given P.G. 600 expressed estrus sooner (P less than .02) after weaning (6.0 vs 7.8 +/- .6 d) and exhibited less (P less than .02) postweaning anestrus (15.6 vs 29.2 +/- 4.0%). Second parity sows that received P.G. 600 showed estrus sooner (P less than .06) than second-parity control sows (4.7 vs 6.4 +/- .7 d). Days to first estrus after treatment did not differ between groups for parity-three and older sows, and percentage anestrus was not different between treatments for parity-two and older sows. The herd X treatment interaction was significant for percentage recycled (percentage of successfully mated sows that returned to estrus), subsequent farrowing rate, and subsequent number of pigs born dead. Number of pigs born alive was lower for sows treated with P.G. 600 than for control sows (10.55 vs 10.10 +/- .18; P less than .02). In summary, treatment of sows weaned in the summer and fall with P.G. 600 had decreased days to postweaning estrus in parity-one and -two sows and reduced frequency of postweaning anestrus in primiparous sows.