In a study on dairy cows, giving a GnRH drug (buserelin) 34 hours after removing a progesterone device made the cows ovulate earlier and more at the same time, but it didn't significantly boost pregnancy rates compared to just giving estradiol.

The objective of the present study was to evaluate whether the inclusion of a gonadotropin-releasing hormone (GnRH) treatment at a novel time (34 h) after intravaginal progesterone device (IPD) removal improves ovulation synchrony and increases fertility in crossbred Girolando dairy cows (B. taurus × B. indicus). A total of 226 crossbred Girolando lactating cows (predominantly 5/8, ¾, and ½ Holstein blood share) were subjected to an estradiol-progesterone based timed artificial insemination (TAI) protocol. At the IPD removal, all cows were treated with 1 mg i.m estradiol cypionate (EC), and then allocated into two groups to receive either 2.5 mL of saline solution (EC-Control, n = 111) or 10.5 μg i.m. buserelin acetate (GnRH analogue) 34 h after IPD removal (EC-GnRH34, n = 115). A subgroup of 30 cows was examined by ultrasonography at 12 h intervals to determine the time of ovulation after IPD removal. All cows were subjected to TAI 48 h after IPD removal. Cows in the EC-GnRH34 group ovulated earlier (60.4 ± 3·8 h, p = 0.03) and more synchronously (100%; p = 0.006) than EC-Control cows (69.8 ± 4·0 h and 60%). Females submitted to the EC-GnRH34 protocol had 42.6% pregnancy per AI (P/AI) compared with 35.1% for the ones treated with EC only (EC-Control, p = 0.24). In conclusion, the present study demonstrated that the ovulation synchrony is optimized with the use of GnRH 34 h after IPD removal. Fertility to the TAI protocol, however, was not significantly improved in comparison with cows treated with a single ovulation inducer, EC.