Buttrey, B.S.Burns, M.G.Stevenson, Jeffrey S.2010-11-292010-11-292010-11-29http://hdl.handle.net/2097/6673Dairy Research, 2006 is known as Dairy Day, 2006Experiments have shown human chorionic gonadotropin (hCG) to be more effective than GnRH as a means to induce ovulation of folli-cles. Dosages used, however, have differed greatly among experiments. A study was per-formed to determine the minimum effective dose of hCG needed to induce ovulation of ovarian follicles in dairy cows. Ovaries of Holstein cows were mapped by using transrec-tal ultrasonography 7 days before a bi-weekly pregnancy diagnosis. Cows were assigned randomly to treatments of saline, 100 μg of GnRH (2 mL of Fertagyl, Intervet, Inc., Mills-boro, NJ), or 500, 1000, 2000, or 3000 IU of hCG (0.5, 1, 2, or 3 mL of Chorulon, Intervet, Inc., Millsboro, NJ). Ovarian structures were monitored again 7 days later, and the propor-tion of cows, and proportion of follicles ≥ 8 mm in diameter, that ovulated were recorded. A dose of at least 1000 IU of hCG resulted in a greater ovulatory response than saline, GnRH, or 500 IU of hCG.DairyGnRHhCGOvulationConference paper