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Effect of Exogenous Progesterone on the Corpora Lutea of Hysterectomized Gilts¹

University of Wisconsin, Madison

Abstract

Four gilts (three open and one bred) were hysterectomized 7 days after the beginning of heat. The corpora lutea were marked with India ink. None of the gilts exhibited estrus before slaughter at 32, 71, 72 and 119 days post heat. The average individual corpus luteum weights and progesterone concentrations of the corpora lutea for the four gilts were 484 mg., 57 ug.; 486 mg., 79 ug.; 305 mg. (not determined); and 414 mg., 12 ug., respectively. Thus hysterectomy caused retention of the corpora lutea for prolonged intervals.

Another experiment involving 32 market gilts was designed to study the effect of progesterone injections on maintenance of the corpora lutea in hysterectomized gilts. All animals were bred on the first day of estrus (day-0); hysterectomy was performed on day-7 and slaughter was on day-25. Progesterone was injected subcutaneously daily from day-10 to slaughter at the rate of 1 mg. per lb. body weight per day. Four groups of gilts were involved: pregnant, pregnant-injected-with-progesterone, hysterectomized, and hysterectomized-injected-with-progesterone. The average individual corpus luteum weights and progesterone concentrations of the corpora lutea from the four respective groups were 419 mg., 34 mcg.; 178 mg., 19 meg.; 421 mg., 42 mcg.; and 181 mg., 26 mcg. Progesterone treatment reduced the corpora lutea weight in both the hysterectomized and non-hysterectomized groups. There was no significant effect of hysterectomy or progesterone treatment on the mean progesterone concentration of the corpora lutea, but progesterone brought about a positive regression of concentration on corpus luteum weight.

Local injections of 4 mg. of progesterone directly into the corpora lutea on the 18th day of pregnancy produced no measurable influence on the average individual corpus luteum weights in two gilts at the 25th day of pregnancy. Two progesterone-treated corpora lutea from each of the two gilts averaged 413 and 412 mg. as compared to an average of 471 and 407 mg. for six and ten untreated corpora lutea from the same gilts.

Transplants of luteal or estrual phase uterine tissue into four gilts hysterectomized on day-7 or -11 of the cycle failed to cause regression of the corpora lutea. The average individual corpus luteum weights for the four gilts were 520, 475, 593 and 517 mg. at 24 to 30 days from their previous estrus. Another gilt in which the nerves associated with the middle uterine artery had been sectioned on day-7 of the cycle returned to heat 21 days post estrus. Evidence from these five gilts fails to demonstrate the role of the uterus in corpus luteum maintenance and regression.

¹ Paper from the Department of Genetics No. 733 and the Department of Animal Husbandry, published with the approval of the Director of the Agriculture Experiment Station.