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Effect of Gonadotropin Dose and Postpartum Status on Induced Ovulation and Pregnancy in Lactating Sows^1,2,

Southern Illinois University, Carbondale 62901

Abstract

The effect of 1,000 or 1,500 IU of pregnant mare serum gonadotropin (PMSG) and 500 or 1,000 IU human chorionic gonadotropin (HCG) given 96 hr post-PMSG on ovulation and pregnancy in 100 lactating sows was studied in a 2 x 2 factorial experiment. Sows were artificially inseminated at 24 and 36 to 42 hr post-HCG. Pregnancy occurred in 76% of the sows treated with 1,500 IU PMSG/1,000 IU HCG versus 56% of the sows given the other three treatments (P<.10). There were no differences among treatment groups in number of corpora lutea or embryos in sows slaughtered at 32 to 36 days postbreeding or in gestation length, litter size or pig birth weight for sows allowed to farrow. In a second experiment, 56 lactating sows were treated with 1,500 IU PMSG plus 1,000 IU HCG given either 72 or 96 hr later. The interval between PMSG and HCG did not affect pregnancy rate, gestation length, litter size or pig birth weight. The results of PMSG-HCG treatment of 282 lactating sows were summarized for an evaluation of the effects of the following factors: number of times the sows had been treated previously; number of pigs born at the prior farrowing; number of pigs nursing; number of days postpartum; season; primiparous versus multiparous at first treatment, and purified, desiccated versus nonpurified, nondesiccated PMSG. The first three factors had no effect on pregnancy rate, ovulation rate, number of pigs born or birth weight. Sows treated 14 to 24 days postpartum had a lower (P<.05) pregnancy rate than those treated 25 to 45 days postpartum, but ovulation rate and litter size were similar. Season had no effect on pregnancy rate but did influence number of pigs born (P<.05). Primiparous sows had a lower (P<.10) pregnancy rate, fewer (P<.10) ovulations and embryos (P<.05), shorter (P<.05) gestations and fewer (P<.05) pigs farrowed than multiparous sows. Use of the purified, desiccated PMSG resulted in a lower (P<.05) pregnancy rate, fewer (P<.05) ovulations and embryos (P<.10) and smaller (P<.05) litters farrowed than nonpurified, nondesiccated PMSG.

¹ This investigation was supported in part by USDA/CSRS ILL-616-15-151.

² The authors would like to thank Russell Snyder and Jim Andruch, swine herdsmen, and Willow Warren for their assistance in the conduct of this project.