Impact of forage allowance using high supplementation on performance and reproductive parameters in Nellore heifers

Abstract

The objective of this study is to evaluate the effects of pasture management using high supplementation in the performance and reproduction parameters of Nellore heifers submitted to 14-15 months of age to fixed time artificial insemination protocol (FTAI). The study will be conducted at APTA (Colina/SP), it will start in the dry season (after weaning) and lasting over the rainy season until the animals enter in the breeding season. Ninety weaned Nellore females (initial body weight of 169 ± 19 kg and 7 months) will be used. The treatments will be different grazing conditions throughout the experimental period, being high and low forage allowance. These conditions will be possible due to two stocking rates (3 or 6 animals/ha) during the dry season and two grazing management heights (25 or 15 cm) during the rainy season. The supplement will be provided daily ad libitum (expected consumption around 1% of BW). The supplement will have 24% crude protein (CP) and 80% total digestible nutrients (TDN) during the dry season. During the rainy season, the supplement will have 20% CP and 80% TDN. Forage mass and chemical composition, body condition score (BCS), body weight, average daily gain and area gain, biometric measurements, carcass ultrasound, blood parameters (reproductive hormones and glucose), liver gene expression (IGF-1, IGFBP-3, pyruvate carboxylase, cytosolic and mitochondrial phosphoenolpyruvate carboxykinase) and reproductive performance (pregnancy rate) will be evaluated. Data analysis will be performed using PROC MIXED and GLIMMIX of SAS, considering a 5% probability for type I error. (AU)