HERITABILITY OF SCROTAL CIRCUMFERENCE ADJUSTED AND UNADJUSTED FOR BODY-WEIGHT IN NELLORE BULLS, USING UNIVARIATE AND BIVARIATE ANIMAL-MODELS

Mixed model methodology under univariate and bivariate animal models w as used to estimate genetic parameters of scrotal circumference (SC) u nadjusted (h(U)(2)) and adjusted (h(A)(2)) for body weight, from field data on 875 Nellore males sired by 80 bulls. The models included rand om effect of animal, the fixed effects of age of dam, year of birth, a nd month and year of measurement, and the covariate age of the animal. In addition,one of the models also included the covariate body weight . Using univariate models, SC estimates of h(U)(2) were 0.18, 0.65, 0. 77 and 0.60, and of h(A)(2) they were 0.15, 0.60, 0.71 and 0.50, at 9, 12, 18 and 24 mo of age, respectively. Bivariate estimates of heritab ility ranged from 0.18 to 0.77 for h(U)(2), and from 0.13 to 0.70 for h(A)(2). The results suggest that it would be better to consider unadj usted SC rather than adjusted SC in selection programs. Bivariate body weight estimates of heritability ranged from 0.15 to 0.45. Genetic co rrelations between SC and body weight ranged from 0.58 to 0.71 when bo dy weight was not included in the model, and from 0.33 to 0.64 when bo dy weight was included. These results suggest that simultaneous select ion for body weight and SC is possible in Nellore cattle. (C) 1998 by Elsevier Science Inc.