R. Bras. Zootec.01/Apr/2017;46(4):309-16.
Associations among growth, scrotal circumference, and visual score of beef cattle in performance tests on pasture or in feedlots
This study aimed to evaluate associations among final weight (FW), average daily gain (ADG), scrotal circumference (SC), and visual score (VS) of beef cattle in performance tests on pasture or in feedlots. Genetic parameters for FW, ADG, SC, and VS of young Nellore bulls performance-tested on pasture or in feedlots were evaluated by mixed model. The performance test and final age were considered as fixed effects and additive genetic and residual effects were considered as random effects. Additive genetic and residual variances for final weight and average daily gain were smaller on pasture than in feedlots. There was no difference between genetic and residual variances and heritability for scrotal circumference on pasture or in feedlots. Genetic variance and heritability for visual score on pasture were smaller than those in feedlots. The posterior means (and highest posterior density intervals with 90% of samples (HPD90) in parentheses) for heritability were 0.46 (0.42; 0.50) and 0.49 (0.41; 0.55) for FW, 0.25 (0.22; 0.29) and 0.25 (0.19; 0.30) for ADG, 0.56 (0.51; 0.61) and 0.60 (0.51; 0.68) for SC, and 0.31 (0.27; 0.34) and 0.42 (0.36; 0.48) for VS on pasture or in feedlots, respectively. The genetic correlations (posterior means with HPD90 in parentheses) were 0.74 (0.69; 0.79) and 0.67 (0.58; 0.77) between FW and ADG; 0.49 (0.43; 0.55) and 0.60 (0.53; 0.68) for FW and SC; 0.79 (0.75; 0.83) and 0.85 (0.80; 0.90) for FW and VS; 0.37 (0.29; 0.46) and 0.34 (0.19; 0.50) for ADG and SC; 0.65 (0.59; 0.71) and 0.74 (0.64; 0.84) for ADG and VS; and 0.46 (0.39; 0.52) and 0.53 (0.44; 0.62) for SC and VS, obtained on pasture or in feedlots, respectively. The genetic and residual (co)variances of growth, scrotal circumference, and visual score of beef cattle vary across environments; however, genetic and residual correlation and efficiency of correlated response among these traits remain constant on pasture or in feedlots.