FATORES RELACIONADOS A PRECOCIDADE SEXUAL E DESEMPENHO PRODUTIVO DE NOVILHAS PRECOCES NELORE

Abstract

The objective of this work was to evaluate the productive performance of precocious and conventional heifers throughout their reproductive life in relation to the weight of the mother and calf produced and to identify factors linked to the sexual precocity of Nellore females from weaning to pregnancy diagnosis. Data were collected over 6 productive years of heifers submitted to the breeding season at 14 months and 24 months of age, evaluating weight at birth and weaning (210 days), carcass conformation score at weaning, offspring weight at birth and weaning, weight of cows at weaning when primiparous, secondoparous and multiparous and pregnancy rate and calculated the weaning ratio with mother weight and calf weight at weaning. In the second work, weight, body condition score, height, meat conformation, carcass ultrasonography and vulvar morphometry were collected from 448 heifers from 3 farms in the state of MS, with collections being carried out at weaning, in the pre-synchronization management, during the TAI protocol and after 30 days of insemination. There was a significant difference for birth weight, with a higher value for conventional primiparous calves compared to early ones (35.37 and 32.28 kg; p=0.0003) and early multiparous calves with a higher value compared to conventional ones (39 .2 and 36.62 kg; p=0.0228). The weaning weight of the calves of the primiparous was higher for the conventional group in relation to the precocious group (199.94 and 172.51 kg; p<0.001). Regarding the weight of the cow at weaning, the conventional group had a higher value than the precocious ones in the categories of primiparous (462.41 and 411.51 kg; p= 0.003), secondary (497.91 and 458.06 kg; p =0.0162) and multiparous (553.33 and 517.70; p=0.003). The weaning ratio was different only in the multiparous category, with a better ratio for precocious compared to conventional ones (41.07 and 38.36%; p= 0.051). The results related to factors linked to precocity showed that there was a difference for age at weaning (236.5 and 229.7 days, P<0,0001), weight at induction (277.5 and 271.07 kg, P<0,0001), length of the vulva (7.98 and 7 .73 cm, P<0,0001), D0 weight (295.8 and 287.3 kg, P=0,023), DG weight (337.43 and 328 kg, P=0,01), ADG from induction to final DG (0.71 and 0.58 kg, P<0,0001) and EGP (4.52 and 4.12 mm, P=0,039) when comparing early and late females respectively. It is concluded that heifers that become pregnant early present lower weight than those that become pregnant at two years of age, but without affecting the efficiency in the production of calves at weaning from second parity, even with a better weaning ratio when multiparous. Heavier, older heifers with greater weight gain after weaning and with greater fat thickness in the rump are more likely to have early pregnancy in their first breeding season after weaning.