Protein requirements for females of Nellore, Nellore × Angus and Nellore × Simmental fed on two forage: concentrate ratios

Evaristo Jorge Oliveira De Souza,Sebastião De Campos Valadares Filho,Rilene Ferreira Diniz Valadares,Marcelo De Andrade Ferreira,Pedro Del Bianco Benedeti,Laura Franco Prados,Marcos Inácio Marcondes,Adriana Guim

doi:10.1590/s1516-35982012000300040

Evaristo Jorge Oliveira De Souza, Sebastião De Campos Valadares Filho + Show 6 more

Open Access

https://doi.org/10.1590/s1516-35982012000300040

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Abstract

This study aimed to determine the protein requirements for females of Nellore, F1 Nellore × Angus and F1 Nellore × Simmental fed on two concentrate levels (30 and 50%). Sixty heifers from three genetic groups with 18 months of age were used: 20 Nellore, 20 Nellore × Angus and 20 Nellore × Simmental. Twelve heifers of the reference group (four of each genetic group) were slaughtered at the beginning of the experiment. Another 12 heifers (four of each genetic group) were fed on the level of maintenance and 36 heifers (12 animals of each genetic group) were kept in power system ad libitum with 30% (six of each group) or 50% (six of each group) dietary dry matter in concentrate. Heifers were randomly assigned to six treatments in a 3 × 2 factorial arrangement (three genetic groups and two diets) with six replicates per treatment. Nine more heifers (three from each genetic group) were used to estimate the apparent digestibility coefficients of food in a parallel experiment. A model was fitted according to the protein retained as function of the gain of empty body weight (EBW) and retained energy (RE) to calculate the protein net requirements. To estimate the metabolizable protein requirements for maintenance the consumption of metabolizable protein was contrasted with EBW. The joint use of the equation net protein gain (NPG) = 197.40 × EBWg - 11.14 × RE is recommended to predict the protein net requirements for weight gain. Protein and metabolizable protein net requirements for maintenance are 1.07 and 3.88 g/EBW0.75/day, respectively. The use efficiency of metabolizable protein for gain of all genetic groups is 37.04%.

Highlights

Requirements of international markets for meat quality compel producers to slaughter young animals, forcing them to accelerate their growth rate, resulting in quality products and higher productivity
The content of defatted dry matter of weight gain, body weight, sex, age and genetic group are the main factors influencing the net requirements of protein for growing and finishing cattle
An overall equation for predicting the empty body weight (EBW) was obtained once the concentrate level, genetic group and the concentrate level × genetic group interaction had no significant effect on this parameter (P>0.05)

Summary

Introduction

Requirements of international markets for meat quality compel producers to slaughter young animals, forcing them to accelerate their growth rate, resulting in quality products and higher productivity. The economic return not always increases with the growth rate improvement, since such expansion often results in increased costs. One of the ways to lower the age of slaughter is the use of cross breeding programs of Bos taurus taurus/Bos taurus indicus, enabling the combination of important productive features, in addition to obtaining the hybrid vigor. The content of defatted dry matter of weight gain, body weight, sex, age and genetic group are the main factors influencing the net requirements of protein for growing and finishing cattle. According to Garrett (1980), breed has much more penetrating influence on the composition of body weight or carcass weight than the nutritional level. The NRC (2000) reports that larger breeds have higher protein requirements at maturity

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