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Influence of Prostaglandin F₂, Dexamethasone, Progesterone and Induced Corpora Lutea on Porcine Parturition¹

University of Wisconsin^,3, Madison 53706

Abstract

The ability of induced corpora lutea (CL) to prevent induction of porcine parturition by dexamethasone or prostaglandin F₂ (PGF₂) was tested in two experiments. In the first experiment, 19 pregnant crossbred sows were injected intramuscularly (IM) with 1,500 IU of Pregnant Mare Serum Gonadotropin (PMSG) on day 104 followed by 1,500 IU of Human Chorionic Gonadotropin (HCG) on day 106. Eight of the 19 sows were also injected IM with 100 mg of dexamethasone/day on days 109 through 112. Five other sows served as untreated controls. Treatment with gonadotropins to induce CL formation increased length of gestation compared to controls (120.0 vs 114.8, SD = 2.3, respectively). Following adjustment by covariance (b = .16, P<.05) for number of induced CL (0 to 27), it was revealed that dexamethasone had no effect on length of gestation in sows containing one or more new CL: PMSG-HCG, 119.4 and PMSG-HCG + dexamethasone, 121.8 days. Litter size, live birth rate and number of CL of pregnancy did not differ among control, PMSG-HCG or PMSG-HCG + dexamethasone-treated sows.

Twenty-eight pregnant crossbred sows and gilts were utilized in the 2 x 3 factorial design of experiment 2 as follows: eight received no treatment and served as controls; eight received IM injections of 500 mg of progesterone in oil/day on days 107 to 114 of gestation andnew CL were induced in 12 using the same doses of PMSG and HCG as was used in experiment 1 with treatment starting on day 99. In half of the females of each group, 5 mg of PGF₂ was infused into a marginal ear vein during a 9-hr period on day 109. Mean lengths of gestation for the six subgroups were: control, 115.5; PGF₂, 110.0; exogenous progesterone, 117.5; exogenous progesterone + PGF₂, 117.5; PMSG-HCG, 117.5; PMSG-HCG + PGF₂, 118.5.

The proportion of piglets born live was lower (P<.01) in females with an additional source of progesterone. Infusion of PGF₂ resulted in a further decrease (P<.05) when premature parturition was prevented. The weight of the CL of pregnancy in pigs with an additional source of progesterone was decreased (P<.01). A further decrease in weight of CL (P<.01) was observed in females infused with PGF₂. Weight of the induced CL was not affected by PGF₂. Serum progestin concentrations of 25 to 30 ng/ml were measured in the PMSG-HCG-treated females on days 107 and 109 and the exogenous progesterone-treated pigs on day 109. Between days 109 and 110 progestin concentrations decreased in all infused and PMSG-HCG-treated females; remained the same in controls and increased further in females treated with exogenous progesterone but not infused with PGF₂. The prepartum decline in serum progestins was similar in all groups.

¹ Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison 53706, Public Health Service Training Grant No. 5-T01-HD-00104-10 from the National Institute of Child Health and Human Development, and Grant No. 630-0505B from the Ford Foundation.

² The authors express appreciation to Ayerst Laboratories for providing the prostaglandin F₂.

³ Department of Meat and Animal Science Paper No. 685.