Ovarian follicular responses in dairy cows treated with GnRH and cloprostenol

Lactating, nonpregnant (with a corpus luteum) Holsteins were given 100 ug GnRH (n = 12) or saline (n = 12) and 500 ug cloprostenol 6 d later. Following luteolysis, ovulation occurred 10.1 +/- 0.2 d (range, 9-12 d) after GnRH and 8.6 +/- 1.0 d (range, 3-12 d) after saline (differences between groups: means, P > 0.05; variability, P < 0.001). Treatment with GnRH and cloprostenol resulted in a relatively synchronous ovulation.