The Effect of Exogenous Progesterone on Formation and Maintenance of the Corpora Lutea and on Early Embryo Survival in Pregnant Swine

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Abstract
The effect of exogenous progesterone on early reproductive performance was studied in 130 gilts. The dosages of hormone were 1 mg. per lb. of body weight during various intervals between zero and 25 days of gestation and 0.4 mg. per lb. of body weight daily from day-10 to day-25 of gestation. Progesterone given daily from time of mating to 96 hours of gestation did not have a significant effect on fertilization rate (97.8% in the controls vs. 100% in the treated), but a higher percent of solid corpora lutea was found in the control group than in the treated group (65 vs. 21; P<.05). Progesterone injected daily during various intervals between zero and 25 days produced no significant beneficial effects on embryo survival. The 18- and 25-day control groups had a significantly higher embryo survival (72% and 83%, respectively) than the two groups treated continuously from breeding to slaughter at the 18th and at the 25th day (1 and 0%), the group treated from breeding to the 18th day and killed on day-25 (0%), the group treated from breeding to day-4 and killed on day-25 (5%), and the group treated from day-4 to day-18 and killed on day-25 (22%). Treatment initiated at day-4 and continued until slaughter on the 18th day as well as treatments initiated on either day-4 or day-18 and continued until slaughter at the 25th day did not appear to have a deleterious effect (means of 96%, 72% and 79%, respectively). Progesterone treatment decreased the average individual corpus luteum weight significantly in every case as compared to the 18- and 25-day control groups. The correlation of percent luteal cells with vesicular nuclei and progesterone concentration was 0.83 (P<.01) between individuals within groups and 0.76 (P<.05) between groups. Embryo and membrane weight did not differ significantly due to progesterone treatment, nor did dosage level have a significant effect upon them. Copyright © . .