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.

Remoção temporária de bezerros em dois momentos do protocolo de sincronização da ovulação GnRH-PGF2alpha-BE em vacas Nelore pós-parto / Temporary weaning of calves at two different times of the GnRH-PGF2alpha-EB synchronization protocol for ovulation in post-partum Nelore cows

Os efeitos da remoção temporária de bezerros (RB) sobre características foliculares e taxas de ovulação e de prenhez de vacas Nelore foram avaliados em dois experimentos quando da inseminação artificial em tempo fixo (IATF), utilizando-se um protocolo à base de GnRH-PGF2α-BE. No experimento 1, 139 vacas Nelore, lactantes, cíclicas ou acíclicas, receberam um protocolo hormonal envolvendo a aplicação de 100±g de análogo GnRH no dia zero (D0-GnRH), 25mg de PGF2α no dia 7 (D7-PGF2α) e 1,0mg de benzoato de estradiol no dia 8 (D8-BE). Os animais foram aleatoriamente distribuídos para serem submetidas ou não à RB (48 horas) antes da aplicação de GnRH (RB1) ou após a aplicação de PGF2α (RB2). Avaliaram-se o diâmetro folicular (DF) nos dias 0 (D0) e 9 (D9) do protocolo e as taxas de ovulação (T0), advindas dos tratamentos. As vacas acíclicas que receberam RB1 apresentaram maiores DF no D0 (P<0,05) e taxa de ovulação (P<0,05) quando da aplicação de GnRH, em relação às que não receberam RB1. Nas vacas cíclicas, não houve efeito da RB1 sobre as variáveis analisadas. As vacas que receberam RB2 apresentaram maiores DF no D9 (P<0,05) e taxa de ovulação (P<0,01) quando da aplicação de BE, em relação às que não receberam a RB2. No experimento 2, 376 vacas da raça Nelore, lactantes, foram submetidas ao mesmo protocolo hormonal e aos mesmos tratamentos do experimento 1, mas foram inseminadas 24 a 30 horas após a aplicação de BE no D8, visando avaliar a taxa de prenhez após a IATF. A taxa de prenhez foi maior nos animais que receberam as duas RB em relação às que não receberam RB (29,8 por cento vs 10,6 por cento; P<0,05). A remoção de bezerros associada ao protocolo hormonal aplicado pode ter aumentado as taxas de prenhez devido às maiores taxas de ovulação, em resposta ao GnRH ou ao benzoato de estradiol.

The effects of temporary weaning (TW) on follicular characteristics and ovulation and pregnancy rates were evaluated in Nelore cows submitted to a fixed-time artificial insemination (TAI) protocol using GnRH-PGF2α-EB. In Experiment 1, 139 cycling or non-cycling suckling Nelore cows received a hormonal protocol based on administration of 100±g of GnRH analog on day zero (D0-GnRH), 25mg of PGF2α on day seven (D7-PGF2α) and 1.0mg of estradiol benzoate on day eight (D8-BE). Cows were randomly assigned to receive or not TW (48 hours) before GnRH (TW1) or after PGF2α (TW2). Follicular diameter (FD) on days zero (D0) and nine (D9) of the protocol and ovulation rates were evaluated. Noncycling cows that received TW1 had larger FD on D0 (P<0.05) and higher ovulation rate after GnRH treatment (P<0.05) than cows without TW1. No effects of TW1 on analyzed variables of cycling cows were observed. TW2 cows had larger FD on D9 (P<0.05) and higher ovulation rate after EB treatment (P<0.01) than cows without TW2. In Experiment 2, 376 suckling Nelore cows were submitted to the same protocols and treatments described in Experiment 1, and artificial insemination was performed from 24 to 30 hours after EB on D8, aiming to evaluate the pregnancy rate after fixed-time artificial insemination. The pregnancy rate was higher in cows submitted to both TW (1 and 2) than in cows without TW (29.8 percent vs 10.6 percent; P<0.05). Temporary weaning associated to the applied protocol may have improved pregnancy rates due to greater ovulation rates after GnRH or EB treatments.