Taxa de prenhez em fêmeas bovinas de corte submetidas à inseminação artificial em tempo fixo no norte de Minas Gerais

Abstract

This work aimed to evaluate pregnancy rate in cows submitted to fixed-time artificial insemination in 32 properties of creation of beef cattle in 18 municipalities of the north region of the state of Minas Gerais The animals were divided into reproductive category and ovarian activity after gynecological evaluation by ultrasonography. The animals with negative diagnosis by cycling or in anestrus were submitted to FTAI protocol, being inseminated 11 days after the application of intravaginal device CIDR®, when, in the removal of the device, temporary weaning (TW) for 48 hours. The results indicate that the variables: reproductive category, body score, diameter of the follicle and presence of corpus luteum in the ovary, reuse of CIDR®, time of insemination, application of ECG, dosage of 200 and 300 IU eCG, removal of calf, genetic group of bulls and inseminator ability were significant p<0.05, in the chi-square test. It was observed that in the reproductive category the smallest pregnancy rate in FTAI was for the primiparous (47,70%), due to their high energy, the highest pregnancy rates in body score was for animals with higher body score, 3.5, (64.39%), the animals with follicular diameter from 8 mm presented the highest pregnancy rate (56,19%), followed of animals with presence of corpus luteum in the ovary (55,43%), evidencing the importance of the ovary structures in the reproductive index. In the reuse of intravaginal devices, the highest pregnancy rate was in use 3 times both in animals cycling as in anestrus. In time of insemination, the highest pregnancy rate was for the females inseminated in the afternoon (54,84%), probably the sperm capacitation occurred in the nocturnal period when the body temperature of the animals is lower. In the application of the ECG, the highest pregnancy rate was for the animals that have applied 200 IU (55,82%), followed of animals that have not applied (52,89%), the ovulatory stimulus TW provided the highest pregnancy rates (53,91%), followed of the application of ECG (53.27%), without significant difference. The zebus bulls provided higher pregnancy rate (54.83%) that taurine ones (48.3%). Inseminators that inseminated from 200 to 500 cows in the breeding season showed higher pregnancy rate (54.55%). With relation to the interaction of body score and the observed variables, the results of pregnancy indicate that animals of larger body score present higher pregnancy rate, confirming the importance of the nutritional condition of animals in the final result of FTAI.