Hormonal Responses of Dairy Cows with Ovarian Cysts to GnRH5

Abstract

Twenty-four cows, diagnosed via rectal palpation as having ovarian cysts were randomly assigned to one of four groups to receive a single IM injection of either 0, 50, 100 or 250 µg of synthetic gonadotropin-releasing hormone (GnRH). Sixteen lactating dairy cows exhibiting clinically normal estrous cycles were used as controls. Of the 18 cows receiving 50, 100 or 250 µg GnRH, 13 (72%) responded to treatment and returned to estrus 20.1 ± 1.5 (range 9 to 27) days after treatment as compared to one of six receiving 0 µg GnRH. Clinical changes in most cases were evidenced by increasing firmness of the cystic structure(s) which subsequently had palpable characteristics similar to corpora lutea. Plasma LH increased significantly (P<.005) on day 0 in cows following injection of GnRH. Differences in plasma LH on day 0 between cows responding or not responding to treatment were not significant. Plasma progesterone and estradiol concentrations on day 0 were higher (P<.01) for cows responding to treatment as compared to those not responding.