Increasing gonadorelin hydrochloride dose at the first GnRH of breeding Ovsynch enhances luteinizing hormone release, ovulatory response, and pregnancy in first-service lactating dairy cows

of DO), with concurrent serum progesterone (P4) sampling. An additional subset of 18 cows had blood samples collected at 0 (pretreatment) and at 30, 60, 90, 120, 150, 180, 210, 240, 300, and 360 min post-treatment to measure LH concentrations. The final statistical model for P/AI included fixed effects of treatment, parity, and their interaction, with random effects of herd, service sire, herd-by-treatment-by-parity, and month fresh nested within herd-by-parity. Treatment and parity significantly affected P/AI, although their interaction was not significant. Least squares means for P/AI were higher with 200 µg than 100 µg GnRH (51.8% vs. 48.6%). When stratified, the effect in primiparous cows was minimal (52.8% vs. 51.8%), but substantial in multiparous cows (50.7% vs. 45.4%). Cows treated with 200 µg GnRH had a greater ovulatory response than those receiving 100 µg (83.0% vs. 70.8%). Parity also influenced ovulation, though no treatment-by-parity interaction was observed. When P4 was categorized (Low