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Growth curves of carcass traits obtained by ultrasonography in three lines of Nellore cattle selected for body weight


The purpose of this study was to evaluate the effect of selection for postweaning weight within the growth curve parameters for both growth and carcass traits. Records of 2404 Nellore animals from three selection lines were analyzed: two selection lines for high postweaning weight, Selection (NeS) and Traditional (NeT), and a control line (NeC), in which animals are selected for postweaning weight close to the average. The measurements were performed: body weight (BW), hip height (HH), rib eye area (REA), backfat thickness (BFT), and rump fat thickness (RFT). Records were collected from 8 to 20 months of age for males and 11 after 26 months of age for females. The parameters A (asymptotic value) and k (growth rate) were estimated by nonlinear models using NLIN procedure of SAS, which included fixed effect of line (NeS, NeT, and NeC) in the model, with the objective to evaluate differences in the estimated parameters in the three lines. The selected animals (NeS and NeT) showed higher growth rates than control line (NeC) for all traits. Line effect on curves parameters was significant (P < 0.001) for BW, HH, and REA in males, and for BFT and RFT in females. Selection for postweaning weight was effective in altering growth curves, resulting in animals with higher growth potential. (AU)