EFEITO DE DIFERENTES MODELOS SOBRE AS ESTIMATIVAS DE (CO)VARIÂNCIAS E PARÂMETROS GENÉTICOS PARA PESOS ATÉ A DESMAMA EM GADO NELORE

We used actual and adjusted weights to 120 d and 210 d of age of 72,731 male and female Nellore calves born in 40 PMGRN - Nellore Brazil herds from 1985 to 2005 aiming to compare the effect of different definitions of contemporary groups on estimates of (co)variance and genetic parameters. Four models, each one with a different structure of contemporary group ( CG ), were compared using the Akaike Information Criterion (AIC), the Bayesian Information Criterion (BIC), and the Consistent Akaike Information Criterion (CAIC). (Co)variance estimates were obtained using a derivative-free restricted maximum likelihood procedure. Estimates of (co)variances and genetic parameters were similar for the four models considered. However, the BIC and CAIC indicated that the most appropriate model for this Nellore population was the one that considered CG to be random, and sex of calf to be fixed and separate from CG , in which CG was defined as the group of calves born in the same herd, year, season of birth (trimester), and undergone the same management. KEYWORDS: beef cattle; contemporary groups; information criteria.