Cattlemen's Day, 2002; Kansas Agricultural Experiment Station contribution; no. 02-318-S; Report of progress (Kansas State University. Agricultural Experiment Station and Cooperative Extension Service); 890; Beef; Ovulation synchronization; Beef cows; Timed AI; GnRH; CIDR


Lactating 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 PGF2αadministration. Cows were assigned to a 2 x 2 factorial arrangement of four treatments: 1) insemination beginning at 48 vs. 60 hours after PGF2αand 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 PGF2αin 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.

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