Effect of EC-GnRH34 timed AI protocol on ovulation synchrony and fertility in crossbred Girolando dairy cows

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.