Effects of endometrial biopsy, uterine culture, and cervical dilatation on the equine estrous cycle.

In 10 mares, lysis of the corpus luteum was induced by endometrial biopsy and culture on day 4 after estrus, as evidenced by a sharp decline in serum progesterone concentration and a shortened interestrous interval. Estrus following the manipulations was prolonged. Endometrial biopsy and culture on days 1 and 3 after estrus or manually dilating the cervix on day 4 after estrus also decreased the serum progesterone concentration (within 24--48 hr after manipulation), shortened diestrus, and prolonged the subsequent estrus. In a 2nd experiment, endometrial biopsy on day 4 after estrus shortened the estrous cycle and diestrous period and prolonged the subsequent estrus. It was postulated that these manipulations stimulated corpus luteum regression, followed by estrus and ovulation in the mare.