Impact of grazing management on growing Nellore heifers with supplementation on performance and reproductive parameters

Abstract

The objective of this project is to study the effects of pasture management with supplementation in the performance and reproduction of Nellore heifers submitted to 14-15 months of age to fixed-time artificial insemination protocol. The study will be conducted at APTA (Colina-SP), starting in the dry season (after weaning) and extending over the rainy season until the animals enter in the breeding season. Ninety newly weaned Nellore heifers (average body weight of 169 ± 19 kg; 7 months) will be used. The treatments will consist of generating different grazing conditions throughout the experimental period, from two grazing management heights, one of 15 cm and one of 25 cm of forage canopy height. The supplement will be provided daily ad libitum (expected intake around 1% of the animal's body weight). The supplement will be formulated to have 24% crude protein (CP) and 75% total digestible nutrients (TDN) during the dry season. During the rainy season, the supplement will have 20% CP and 80% TDN. Forage mass and morphological composition, bromatological pasture analysis, body condition score (BCS), body weight, average daily gain and area gain, biometric measurements, carcass ultrasound (longissimus muscle area, subcutaneous fat thickness, ratio, marbling and fat thickness in P8), blood parameters (reproductive hormones and glucose), liver gene expression (IgF-1, IGFBP-3, pyruvate carboxylase, cytosolic phosphoenolpyruvate carboxykinase mitochondrial) and reproductive performance (final pregnancy rate) will be evaluated. Data analysis will be performed using the PROC MIXED and GLIMMIX of SAS, considering 5% probability for type I error. (AU)