THE RÔLE OF THE UTERUS IN OVARIAN CONTROL IN THE MARE

in Reproduction

Summary.

The effect of hysterectomy on ovarian activity was studied in four mares. The cyclic secretion pattern of plasma progestins normally observed in the intact mare was interrupted by hysterectomy. Follicular activity was observed in all four hysterectomized mares, in spite of prolonged luteal activity, with a large number of follicles attaining ovulatory size without the occurrence of ovulation. Some ovulations were observed at irregular intervals in two out of four hysterectomized mares in spite of plasma progestin levels which ranged from 2 to 6 ng/ml. While all ovulations which occurred in the hysterectomized mares were followed by the formation of CL as determined by palpation per rectum, the rise of progestins in the peripheral plasma was variable as significant increases followed CL formation in some instances but not in others. Four mares had CL with functional life spans of 48, 74, 75 and 77 days at the time the experiment was terminated. There was no difference in the ability of the CL formed following these ovulations to convert pregnenolone to progesterone (per unit weight) as compared to CL of 9 days duration. The longest estimated CL life span in any hysterectomized mare was 137 days. Sexual receptivity did not occur in conjunction with follicular growth and ovulation in the hysterectomized mares in the presence of an active CL.

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