THE EFFECT OF ESTRADIOL CYPIONATE (ECP) ON OVARIAN FOLLICULAR DEVELOPMENT AND OVULATION IN DAIRY-CATTLE

The efficacy of estradiol cypionate (ECP) for synchronizing ovarian fo llicular development was determined in lactating Holstein-Friesian cat tle. In Experiment 1, 13 cattle were given simultaneous intramuscular (IM) injections of 100 mg progesterone and 0 (control), 0.5 or 1.0 mg ECP on Day 3, after a synchronized ovulation (Day 0). Maximum diameter of the dominant follicle of Wave 1 was significantly larger in contro l cattle than in those given 0.5 or 1.0 mg ECP (means: 15.7, 13.2, and 12.9 mm, respectively). Mean day of emergence of Wave 2 was significa ntly later in controls than in those given 1.0 mg ECP, with the 0.5 mg group intermediate (Days 10.2, 8.8 and 9.5, respectively). In Experim ent 2, 14 cattle were given a CIDR-B and IM injections of 1 mg ECP and 50 mg progesterone without regard to stage of cycle (treatment = Day 0). On Day 8, the CIDR-B was removed and 500 mu g cloprostenol injecte d, IM. Mean days of wave emergence (Day 3.4; range: -2 to 7) and ovula tion (Day 12.1; range: 10 to 14) indicated that ECP had limited effica cy for synchronizing follicular development and ovulation in dairy cat tle when given at random stages of the estrous cycle.