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Maintenance of Early Pregnancy in Ovariectomized Gilts Treated with Gonadal Hormones¹

University of Wisconsin, Madison

Abstract

Studies were made to determine the hormonal requirements for the maintenance of early pregnancy in swine. Nine control and 27 treated gilts were used. Ovariectomy was performed on day-4 and autopsy on day-25 of pregnancy. Subcutaneous injections of progesterone and estrone at a ratio of 4000:1 were administered in three different dosage levels per pound body weight, daily: (1) 0.3 mg. progesterone plus 0.075 meg. estrone, (2) 0.6 mg. progesterone plus 0.15 mcg. estrone (3) 1.2 mg. progesterone plus 0.3 meg. estrone. Injections were started 72 hours after breeding and were continued to slaughter.

The numbers of gilts out of nine that were pregnant at day-25 of gestation were 8, 8, 9 and 8 for the three treated and control groups, respectively. The average percentages of embryo survival (for all gilts per group) and the average numbers of live embryos (per pregnant gilt) in the three treated groups were significantly less than for the control group (17, 4.1; 45, 4.6; and 38, 5.2 vs. 86, 11.8). There were significantly greater average numbers of dead embryos at autopsy in the three treated groups than in the control group (3.6, 2.1 and 1.8 vs. 0). The group receiving the lowest hormone level also had a significantly greater average number of dead embryos as compared to the group receiving the highest hormone level (3.6 vs. 1.8). Embryo and membrane weights averaged 0.39, 5.9; 0.47, 7.8; 0.48, 7.7; and 0.51, 9.2 gm. for the three treated and control groups respectively. These means were not significantly different.

¹ Paper from the Department of Genetics No. 734 and the Department of Animal Husbandry, published with the approval of the Director of the Agriculture Experiment Station.