ARS | Publication request: Strategies to improve fertility in post partum Bos indicus cows submitted to a fixed-time insemination protocol with GnRH and PGF2a

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 4, 2009
Publication Date: N/A

Interpretive Summary: Fertility of Bos indicus cows to a timed artificial insemination was evaluated following pretreatment with progesterone for either 7 or 14 days to induce estrous cyclicity and control follicular wave development and temporary calf removal. Nelore cows (n = 283), from commercial research herds in Brazil received a progesterone intravaginal device (CIDR) for 7 or 14 d prior synchronization of ovulation using the CO-Synch protocol and timed insemination. These cows were also divided to receive either temporary weaning or no weaning for 48 h before each GnRH injection of the CO-Synch protocol. Effects of progesterone pretreatment and temporary weaning on ovulatory follicle size and ovulation to each GnRH treatment were measured. Progesterone treatment and cyclicity status affected ovulatory follicle diameter and cyclicity and temporary weaning affected ovulation response to the first GnRH injection, but none of these variables affected ovulatory diameter, ovulation response or fertility after the second GnRH injection. In the second study, we evaluated the effect of no treatment and treatment with or without a CIDR device between GnRH and PGF2a treatments of a modified CO-Synch protocol on pregnancy rate to TAI, and throughout a 90-d breeding season in suckled Bos indicus Nelore cows (n = 453). The inclusion of a CIDR between first GnRH and PGF2a treatments of a modified CO-Synch protocol did not improve pregnancy rate (29% and 33% for cows receiving CO-Synch + CIDR and CO-Synch protocol, respectively), and cycling cows had poorer TAI pregnancy rates than anestrous cows treated with either protocol (21.7% vs. 40.7%; P < 0.05). However, regardless of treatment with CIDR, cows submitted to TAI protocol had greater (P < 0.05) pregnancy rates at 30 (54.8% vs. 11.2%), 60 (72.1% vs. 38.8%), and 90 d (82.0% vs. 57.9%) of breeding season than untreated cows.

Technical Abstract: In Experiment 1, we evaluated the effects of two lengths of progesterone exposure (CIDR; 7 vs. 14 d) prior to a modified CO-Synch protocol, with or without temporary weaning (TW) before GnRH treatments, on fertility of suckled Bos indicus Nelore cows (n = 283) and on calf performance. Timed AI (TAI) pregnancy rates for cows receiving 7 d CIDR + TW, 7 d CIDR, 14 d CIDR + TW, and 14 d CIDR were 53%, 47%, 46%, and 41%, respectively (P > 0.10). Calves submitted to two 48 h TW 6 d apart had lower mean body weight at 240 d (187.9 ± 2.7 Kg vs. 195.5 ± 2.7 Kg; P < 0.05), but weight at 420 d was not affected by TW (240.1 ± 5.1 Kg). In Experiment 2, we evaluated the effect of no treatment and treatment with or without a CIDR device between GnRH and PGF2a treatments of a modified CO-Synch protocol on pregnancy rate to TAI, and throughout a 90-d breeding season in suckled Bos indicus Nelore cows (n = 453). The inclusion of a CIDR between first GnRH and PGF2a treatments of a modified CO-Synch protocol did not improve pregnancy rate (29% and 33% for cows receiving CO-Synch + CIDR and CO-Synch protocol, respectively), and cycling cows had poorer TAI pregnancy rates than anestrous cows treated with either synchronization protocol (21.7% vs. 40.7%; P < 0.05). However, regardless of treatment with CIDR, cows submitted to TAI protocol had greater (P < 0.05) pregnancy rates at 30 (54.8% vs. 11.2%), 60 (72.1% vs. 38.8%), and 90 d (82.0% vs. 57.9%) of breeding season than untreated cows.