Avaliação de parâmetros associados à precocidade sexual de novilhas Nelore em sistemas integrados de produção

Abstract

This study aimed to evaluate the serum concentration of insulin­like growth factor type I (IGF­I); follicular diameter; fat thickness on the rump (EGP8); average weight gain in Nellore heifers subjected to different integration systems. For this purpose, prepubertal heifers (n = 48) aged between 14 and 16 months and an initial average live weight of 270 ± 36 kg, were distributed following a randomized block design, with four replications in the production systems: exclusive livestock (PEC); crop­livestock integration (ILP) and livestock­forest integration with eucalyptus in single rows (IPFs) and triple (IPFt). During the 210­day experimental period (May­November / 2019) heifers were subjected to transrectal ultrasound every ten days to detect the diameter of the largest follicle present. On the same day, blood samples were collected to measure IGF­I. The animals were weighed every 28 days, after a 16­hour fast. EGP8 measurements were collected at three points: July, August, and October. The microclimate was evaluated using the black globe temperature and humidity index (ITGU) and radiant thermal load (CTR), with monthly averages calculated between 7 and 18 hours. It was observed that the animals spent a longer period of heat stress in all treatments based on the values of ITGU and CTR. The thermal comfort indexes were better in the treatments that included the forest component. The highest serum concentration of IGF­I was obtained by heifers of the IPFt systems; however, the follicular diameter did not differ between treatments. The greatest weight gain and measurement of EGP8 were obtained by animals of the ILP system. Therefore, it is concluded that the implantation of integrated production systems makes it possible to obtain better parameters that associate sexual precocity with Nellore heifers.