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Induced Ovulation and Conception in Lactating Sows^{1 ,2,}

Southern Illinois University, Carbondale 62901

Abstract

Fifty lactating sows were injected with 1,500 IU pregnant mare serum gonadotrophin (PMSG) at an average of 25 days postpartum. Twenty-four of these sows received prostaglandin F₂ (PGF₂) 24 hr prior to PMSG. Ninety-six hours after the PMSG injection, 1,000 IU of human chorionic gonadotrophin (HCG) were injected. Artificial insemination was performed at 24 and 36 to 42 hr post-HCG. The PMSG/HCG treatment resulted in pregnancy in 17 of 20 sows slaughtered from 34 to 43 days postbreeding and in 23 of 30 sows allowed to complete gestation. Mean numbers of corpora lutea (33) and viable embryos (15) were counted at slaughter. Litter sizes were averaged (11) for those sows allowed to farrow. Treatment with PGF₂ prior to PMSG injection had no effect on conception rates, number of corpora lutea, number of embryos or litter size in the lactating sows. In a second experiment, the same hormone treatments were administered to lactating sows beginning on day 5, 10, 15 or 20 postpartum. Pregnancy rates were 0/10, 2/10, 8/10 and 6/10, respectively (P<.05, chi-square). At slaughter (30 to 40 days postbreeding), corpora lutea and embryo numbers recorded from pregnant sows were 23.0, 9.5; 31.5, 15.3, and 28.0, 18.8, respectively, for the sows in the day 10, day 15 and day 20 groups. In a third experiment, sows were given PMSG-HCG as previously described on either day 5 (five sows) or day 10 (14 sows) postpartum. Laparotomy of these sows 2 to 5 days postbreeding revealed minimal ovarian responsiveness at day 5, but 43% of the animals responded with multiple ovulations at day 10. The low pregnancy rate seen at day 10 in Exp. 2 may reflect embryonic mortality due to unfavorable uterine environment. We conclude that the PMSG/HCG treatment followed by timed artificial insemination of lactating sows will induce ovulation and conception as early as 15 days postfarrowing. Pregnancy is thus concurrent with lactation, eliminating the need for early weaning and reducing the interval between successive farrowings.

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

² The authors would like to thank Russell Snyder, the swine herdsman, for his assistance in carrying out this project.