Different supplementation strategies during rearing and their effects on the development of the reproductive tract and the response to puberty induction in Nelore heifers

Abstract

The performance of beef heifers during the rearing phase is crucial for improving the productivity and sustainability of the beef production chain. Weight gain during this phase can be impacted by the qualitative and quantitative aspects of pastures, and the sexual precocity of future breeding stock can be affected. In this regard, this research aims to evaluate how supplementation during rearing impacts the development of the reproductive tract and precocity of zebu heifers, as well as the response to the puberty induction protocol. Sixty-four newly weaned Nellore heifers, approximately 8 months old and weighing 250 kg of body weight (BW), will be randomly assigned in a completely randomized design and subjected to four treatments based on the level of supplementation during the rearing phase: T1 - Low (0.03 g/kg of BW), T2 - Marginal (0.3 g/kg of BW), T3 - Medium (0.6 g/kg of BW), T4 - High (0.9 g/kg of BW). The phase will last 7 months, during which the live weight of the animals will be evaluated every 28 days to calculate the average daily gain (ADG), as well as their body condition score (BCS). At the beginning and end of the rearing phase, the heifers will have their blood collected for leptin hormone evaluation at 12 and 14 months and will undergo reproductive evaluation and had their subcutaneous fat thickness measured at 8, 12 and 14 month. After the last evaluation, the hormonal protocol for puberty induction will be applied. At the end, a new evaluation will be performed, as well as an analysis of the response to puberty induction in the animals. Phenotypic data will be analyzed by analysis of variance using linear models. With this study, we aim to elucidate how the level of supplementation during rearing influences the performance and reproductive characteristics of Nellore heifers.