Net requirements of energy, protein and macrominerals for weight gain of grazing beef cattle castrated at different ages, with and without supplementation

Anilza Andréia Da Rocha,Henrique Jorge Fernandes,Lívia Vieira De Barros,Aline Gomes Da Silva,Daniel Mageste De Almeida,Sidnei Antonio Lopes,Leandro Galon,Mário Fonseca Paulino

doi:10.1590/s1516-35982012000200025

Abstract

The objective of this experiment was to estimate the requirements of energy, protein and macrominerals of grazing crossbreds calves, in Brachiaria decumbens Stapf pasture, castrated at different ages, with and without supplementation. Forty-seven young calves at initial age of 120±30.1 days and 115.3±1.97 kg of live weight were used. To estimate net energy requirements for weight gain, a regression equation between energy retained in the gain and empty body weight gain and metabolic empty body weight was obtained. For estimation of net protein requirements for weight gain, a regression equation was adjusted between protein retained in gain and empty body weight gain and energy content of this gain. Net requirements of Ca, P, Mg and Na for weight gain were determined by the equation Y' = a.b. Xb-1, in which a and b represent the intercept and the coefficient of the alometric equation of macromineral body content prediction, respectively. Neither castration nor concentrate supplementation affects body weight gain net requirements, except the ones of Ca, which were higher for non-castrated animals.

Highlights

Cattle production in Brazil is mainly pasture-extensive
To estimate net energy requirements for weight gain, a regression equation between energy retained in the gain and empty body weight gain and metabolic empty body weight was obtained
For estimation of net protein requirements for weight gain, a regression equation was adjusted between protein retained in gain and empty body weight gain and energy content of this gain

Summary

Introduction

Cattle production in Brazil is mainly pasture-extensive. there is little information on animal requirement in the Brazilian pasture regime (Fontes 1995; Zervoudakis et al, 2002; Fregadolli, 2005; Moraes, 2010). The net energy system, developed by Lofgreen & Garrett (1968), is the basis of the NRC (2000), a model adopted worldwide for diet formulation for beef cattle (Tedeschi et al, 2002). This system sorts nutritional requirements for maintenance and weight gain (growth and weight gain). Maintenance and gain needs represents the net requirement of the animals. Requirements of metabolizable nutrients can be obtained from use efficiency factors of feed energy for maintenance and gain

Objectives

Methods

Results

Conclusion