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Abstract
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 g and 100 g; 50 g and 50 g; 100 g and 50 g; 50 g and 100 g). 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.