Strategies to improve fertility in postpartum multiparous Bos indicus cows submitted to a fixed-time insemination protocol with gonadotropin-releasing hormone and prostaglandin F2alpha.
In Exp. 1, we evaluated the effects of 2 lengths of progesterone exposure [CIDR (controlled intravaginal drug release); 7 vs. 14 d] before a modified CO-Synch protocol [50.0-microg injection of GnRH 6.5 d before a 25.0-mg injection of PGF(2alpha) followed by another injection of GnRH and fixed-time AI (TAI) 2 d after PGF(2alpha)], with or without temporary weaning (TW) before GnRH treatments, on fertility of suckled multiparous Bos indicus cows (n = 283) and on calf performance. Timed AI 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 decreased mean BW at 240 d (187.9 +/- 2.7 vs. 195.5 +/- 2.7 kg; P < 0.05), but BW at 420 d was not affected by TW (240.1 +/- 5.1 kg). In Exp. 2, we evaluated the effect of no treatment and treatment with or without a CIDR insert between GnRH and PGF(2alpha) treatments of a modified CO-Synch protocol on pregnancy rate to TAI, and throughout a 90-d breeding season in suckled multiparous Bos indicus cows (n = 453). The inclusion of a CIDR between first GnRH and PGF(2alpha) 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.
Departamento de Produção Animal, Faculdade de Medicina Veterinária e Zootecnia-UNESP, P 18618-000, Brazil.
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D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D005298:Fertility / Q000187:drug effects* / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006728:Hormones / Q000494:pharmacology*; D007315:Insemination, Artificial / Q000379:methods / Q000592:standards / Q000662:veterinary*; D006080:Ovarian Follicle / Q000187:drug effects; D010060:Ovulation / Q000187:drug effects; D010120:Oxytocics / Q000494:pharmacology*; D011247:Pregnancy; D018873:Pregnancy Rate
D006728:Hormones; D010120:Oxytocics; D007987:Gonadotropin-Releasing Hormone; D015237:Dinoprost