Estimativas de parâmetros genéticos para características de carcaça avaliadas por ultrasonografia em bovinos da raça Guzerá

Abstract

Genetic parameters were estimated for body weight and real-time ultra-sound loin-eye area, rump fat thickness and back fat thickness of 1,317 Guzera cattle, 90,4% yearling bulls and 9,6% heifers. Animals were raised in four different farms located in the State of São Paulo State, Brazil. Analyzed models included the effects of age and 43 contemporary, accordingly to herd, sex, nutritional management and the date the animals were measured. Variance and covariance components were estimated using REML methodology and MTDFREML software. Single trait analyze were used to produce repeatability and heritability estimates for the four traits. Multiple trait analyzes were used to estimated genetic correlations among the traits. Repeatability estimates were .44 (body weight), .39 (loin-eye area), .75 (rump fat thickness) and .49 (back fat thickness). Heritability estimates were .41 (body weight), .34 (loin-eye area), .32 (back fat thickness) and .10 (rump fat thickness). Genetic correlation estimates were .79 (between body weight and loin-eye area), .20 (between body weight and back fat thickness), .05 (between loineye area and rump fat thickness), .02 (between loin-eye area and back fat thickness) and .64 (between the two measurements of fat thickness ). Results suggest that there is no need for repeated real-time ultra-sound in order to evaluate carcass traits, and that direct selection for these traits might be effective. In addition, there is no genetic antagonism between selection for body weight, usually adopted by zebu cattle breeders as a selection criterion, and carcass traits.