Johnson, Sandra K.Harmoney, Keith R.Stevenson, Jeffrey S.2010-08-062010-08-062010-08-06http://hdl.handle.net/2097/4575Lactating beef cows (n=360) were synchronized using the Cosynch procedure; 100 μg of GnRH (day −7) followed in 7 days by 25 mg of PGF2α (day 0). A used intravaginal progesterone insert (CIDR-B) was inserted on day −7 and removed at the time of PGF2α administration. Cows were assigned to a 2 × 2 factorial arrangement of four treatments: 1) insemination beginning at 48 vs. 60 hours after PGF2α and 2) administration of a second, 100 μg injection of GnRH or an equivalent volume of saline immediately after timed AI. Timed AI at either 48 or 60 hours after PGF2α in a Cosynch + CIDR protocol was equally effective. Administration of GnRH at timed AI improved conception in all cycling cows and in some noncycling cows, depending on their progesterone status.BeefOvulation synchronizationBeef cowsTimed AIGnRHCIDRConference paper