323 - CANCELLED: Effects of Slaughter Weight and Sex on Multivariate Fat Allometric Coefficients for Determination of Optimal Slaughter Points on Crossbred Angus X Nellore Steers and Bulls

Abstract: Animal breed, sex, age, and nutrition dynamically affect tissue deposition and requirements which cumulatively represent economic losses due to suboptimal slaughter points in varied animals. Herein, we investigate the potential implementation of principal components analysis (PCA) of carcass fat and live biometric measures (BM) collected in bulls and steers fed similar dietary regimens for detection of a multivariate representation of allometric growth desirable across sex to determine optimal slaughter points. A total of 40 F₁ Angus x Nellore bulls and steers 12.5 ± 0.51 mo. of age, with an average shrunk BW of 233 ± 23.5 and 238 ± 24.6 kg for bulls and steers, respectively, were randomly distributed into a 1+2 x 3 factorial arrangement (1 reference group, 2 sexes, and 3 slaughter weights) with eight animals (4 bulls and 4 steers) slaughtered at the start of the trial and served as reference. The rest were slaughtered once average body weights (BW) of the group reached 380 ± 19.5 (6 bulls and 5 steers), 440 ± 19.2 (6 bulls and 5 steers), and 500 ± 19.5 kg (5 bulls and 5 steers). Variance explained by the first principal component (PC1) differed among the slaughter weights and sex. Fat deposition for steers was more homogeneously and highly correlated in the multivariate space (MS) for BW < 380kg, whereas for bulls, fat deposition was more scattered and less correlated. For BW > 380kg, the opposite was observed. Bulls had a more homogeneous distribution in MS with higher correlation, and the steers had a more heterogeneous contribution. The highly significant differences between the MS along PC1 highlight the different dynamics of nutrient deposition for bulls and steers in different stages of growth. Therefore, provided with an adequate nutrition, carcass homogeneity is higher for bulls slaughtered at heavier BW.