Evaluation of the effectiveness of decreasing the dose of GnRH used for synchronization of ovulation and timed AI at first service in dairy cows
McKee, Lauren Elizabeth
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The objective was to determine the effectiveness of decreasing the dose of GnRH used for synchronization of ovulation. First service lactating Holstein cows (n=100) at the University of Georgia Dairy in Athens were randomly assigned to 1 of 4 treatment groups using different doses of GnRH (100 µg and 100 µg; 50 µg and 50 µg; 100 µg and 50 µg; 50 µg and 100 µg). All cows received 25 mg of PGF2a 11 days (d -11) prior to starting Ovsynch. Blood samples were collected on days -11 and 0 for progesterone analysis. Cows received GnRH on day 0, PGF on day 7, and GnRH on day 9. Cows were artificially inseminated (AI) 16-20 hours after the second GnRH injection. Pregnancy was checked via ultrasound at 35-40 days and 55-60 days after AI. Pregnancy rates did not differ among treatments. Cows that were cycling were more likely to be pregnant.