Presynchronization with gonadotropin-releasing hormone increases the proportion of Bos indicus-influenced females ovulating at initiation of synchronization but fails to improve synchronized new follicular wave emergence or fixed-time artificial insemination conception rates using intravaginal progesterone, gonadotropin-releasing hormone, and prostaglandin F^sub 2[alpha]1

摘要

The objectives were to evaluate the effect of presynchronization with GnRH on pregnancy rates (Exp. 1) and ovarian events (Exp. 2) in Bos indicus-influenced females synchronized with CO-Synch + controlled internal drug release (CIDR) as described below. In Exp. 1, a total of 135 Brahman x Hereford (F1) females were assigned randomly after stratification to 1) Presynch; presynchronization followed by CO-Synch + CIDR, or 2) No Presynch; CO-Synch + CIDR without presynchronization. On d - 7, cattle received 100 pg of GnRH or 2 mL of intramuscular (i.m.) saline. On d 0, all cattle received a CIDR and i.m. injection of GnRH (GnRH-1), followed by CIDR removal and i.m. injection of 25 mg of PGF^sub 2α^ (PGF) Ofl d 7, and i.m. injection of GnRH (GnRH-2) and timed Al (TAT) 66 h after CIDR removal (d 10). An additional 77 cows not involved in the Presynch comparison werealso treated with CO-Synch + CIDR. Pregnancy rates for Presynch (37.3 ± 6%) and No Presynch (48.5 ± 6.1%) did not differ (P 0.6). Pregnancy rate for all CO-Synch + CIDR-treated cattle combined was 41.9 ± 6.1 (n = 145). Tn Exp. 2, we examined ovarian events in 98 Brahman x Hereford (F1) cows assigned randomly to Presynch or No Presynch. Ovulatory response to GnRH-1 was greater (P < 0.01) in the Presynch (58 ± 7.1%) than in the No Presynch (27.1 ± 6.5%) group. However, emergence of a synchronized new follicular wave after GnRH-1 and ovulation rate after GnRH-2 did not differ between groups (P 0.4). Presynchronization increased the proportion of females ovulating after GnRH-1, but this did not increase synchrony of new follicular wave emergence or ovulation after GnRH-2, and did not improve TAI pregnancy rates. [PUBLICATION ABSTRACT]