Efeitos do uso de GNRH no momento da IATF e dias pós-parto sobre a taxa de prenhez em vacas de corte com cria ao pé / Effects of the use of GnRH in the moment of fixed-time artificial insemination and postpartum days on the pregnancy of the nursing beef cows

RESUMO

A falha na detecção de estros e o anestro pós-parto são as principais causas da baixa fertilidade nos rebanhos bovinos. Para minimizar estes problemas uma das biotecnologias recomendadas é o emprego da Inseminação Artificial em Tempo Fixo (IATF). O trabalho avaliou o uso de GnRH no momento da IATF e o número de Dias Pós-Parto (DPP) sobre o desempenho reprodutivo. Foram utilizadas 32 vacas de corte com cria ao pé, 15 vacas formaram o grupo GnRH e 17 o grupo controle. As vacas estavam com data média de 74 DPP por ocasião da IATF.Os animais formavam um grupo homogêneo sendo manejados em iguais condições.As vacas receberam no dia “0” 2 mg de benzoato de estradiol e implante intravaginal de progesterona usado previamente (2º uso), no 6º dia foi aplicado 0,375 mg de Cloprostenol Sódico e no 8º dia, pela manhã, foram retirados os implantes, separados os bezerros e foi aplicado 0,5 mg de cipionato de estradiol. No dia 10º dia pela tarde procedeu-se a IATF. Neste momento, aleatoriamente, de cada duas vacas uma recebia 100μg de análogo sintético ao GnRH. Sete dias após a IATF os animais

ABSTRACT

The lack of estrous detection and the postpartum anestrous are the largest causes of the low fertility in the beef cattle herds. To minimize these problems one of the recommended biotechnology it is the use of the fixed-time artificial insemination (TAI). This work evaluated the use of GnRH at the moment of TAI and the postpartum days (PPD) on the reproductive performance. Data of the thirty two cows rearing calves were used. Fifty cows formed the group GnRH and 17 the group control. The PPD of the cows were in medium 74 days for occasion of TAI. The animals formed one homogeneous group being handled equally. All cows received in the day “0” 2 mg of estradiol benzoato and one intravaginal implant content progesterone of 2nd use. On the 6th day was applied 0,375 mg of sodic cloprostenol and in the 8th day, by the morning, the implants were take off and the calves were separated temporarily and were applied 0,5 mg of estradiol cipionate. On the 10th day at the afternoon TAI was done. At this time randomly, one of each two cows received 100 µg of synthetic analogue to GnRH. Seven days after TAI the animals were allocated into one field with more 35 cows and 2 clean-up bulls during 60 days. It was evaluated the effects on the GnRH application on the Pregnancy rate at TAI (PRTAI) and the pregnancy rate after clean-up bulls (PRB). The effects of the PPD were analyzed on the PRTAI and PRB. The PRTAI was of 46.7% and 35.3%, respectively for the cows of the groups GnRH and control (P>0.05). The PRB was of 53.3% and 64.7%, respectively for the cows of the group GnRH and control (P>0.05). There was not relationship by the use of GnRH with PRTAI and PRB. For analyze the PPD it was formed two groups. One group (14 cows) with average of 57 ± 18.4 PPD (PPD57) and other group (18 cows) with average of 88 ± 9.1 PPD (PPD88). In the groups PPD57 and PPD88 the PRTAI was respectively 42.9% and 38.9% (P>0.05); and the PRB was respectively 64.3% and 55.6% (P>0,05)