M. M. de Alencar

Prediction of the chemical body composition of Nellore and crossbreed bulls

Young Nellore and crossbreed bulls were comparatively slaughtered to generate equation models for predicting the chemical composition of the empty body and carcass from the chemical composition of the Hankins and Howe section (; ). Data were collected from 236 animals from different genetic groups: Nellore, one-half Canchim + one-half Nellore, one-half Angus + one-half Nellore, and one-half Simmental + one-half Nellore, with 48 baseline animals (BW range from 218 to 433 kg) and 188 animals finished in the feedlot (BW range from 356 to 618 kg). The chemical composition prediction equation model was developed for all genetic groups using stepwise regression analysis. Across all animals, the percentages of water and ether extract in the HH section were highly correlated ( < 0.001) with the percentages in the carcass ( = 0.911 and = 0.901, respectively, for water content of the carcass [HOC] and = 0.921 and = 0.921, respectively, for ether extract content of the carcass [EEC]) and empty body ( = 0.937 and = 0.926, respectively, for water content of the empty body [HOEB] and = 0.935 and = 0.939, respectively, for ether extract content of the empty body [EEEB]). The best prediction models were for the traits of empty body weight, HOEB, EEEB, HOC, and EEC. Determination coefficients for predicting the dependent variables obtained from the carcass composition were lower than those obtained from the empty body composition. It was concluded that the chemical composition of the empty body and the carcass can be predicted from the composition of the HH section, using a general equation for different genetic groups.

Differences in residual feed intake are largely explained by changes in body composition

Genetic selection of efficient animals can result in lower costs, reduced environmental impact and increased profitability. The associations between feed efficiency selection and performance are known, however the possible impacts on body composition of Nellore are still unknown. Residual feed intake (RFI), defined as the difference between observed and predicted intake (predicted from metabolic body weight and daily gain) (Koch et al., 1963), has been proposed as an index for genetic selection, however, differences in body composition have been pointed out as a limiting factor in the use of RFI for cattle selection (Herd and Pitchford, 2011). The objective of this work was to examine the relationship between RFI and body composition in Nellore steers.