Arquivo Brasileiro de Medicina Veterinária e Zootecnia (Feb 2009)
Remoção temporária de bezerros em dois momentos do protocolo de sincronização da ovulação GnRH-PGF2α-BE em vacas Nelore pós-parto Temporary weaning of calves at two different times of the GnRH-PGF2α-EB synchronization protocol for ovulation in post-partum Nelore cows
Abstract
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 (PThe 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% vs 10.6%; 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.
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