ABSTRACT - The objectives of this study were to obtain adjustment factors for effects of calf age, dam age and calf Julian birth date on weight gain from birth to weaning (GND) and on visual scores of conformation (C), precocity (P), and muscling (M) and to estimate effects of maternal and individual heterosis on those traits. The analyzed records were from two breeding programs named Natura and Conexão Delta G, totalizing 187,610 purebred and crossbred Nellore x Angus and Nellore x Hereford calves. Calves were born between 1989 and 1999 in herds located in different states of Brazil. The statistical models applied to analyze GND and visual scores of C, P, and M included fixed effects of contemporary group, calf age (quadratic regression), dam age (quadratic-quadratic polynomial regression with junction point at seven years), calf Julian birth date (quadratic-quadratic-quadratic polynomial regression with junctions at 165 and 260 days for GND, 150 and 240 days for C, 165 and 270 days for P, and 155 and 260 days for M), and individual and maternal heterozygosity (linear regressions). All effects included in the model showed significant influence on GND and on visual scores of C, P, and M. The estimated values of maternal and individual heterosis were, respectively, 8.9% and 9.9% for GND; 10.0% and 6.6% for C; 8.5% and 4.8% for P; and 10.9% and 5.0% for M.
adjustment factors; conformation; crossbreeding; muscling; precocity
