Estimation of Phenotypic and Genetic Parameters and Genetic Trend of Weights in the Weaning Phase (P205), Weight at one Year (P365), the Yearling (P505) in Nellore Cattle in the Northern Region and Under-Region Middle-North of Brazil

We studied 257 herds of 257 farms, totaling 79,051 observations in eight States of the Federation, which genetic and phenotypic parameters were estimated for the weights to 205 (P205), 365 (P365) and 550 days old (P550) of Nelore, included in the system of development Control by weight (CDP) conducted by the Brazilian Association of Zebu breeders (ABCZ) and raised in the northern region and sub-region Means North. Estimates of variance components and genetic parameters were obtained by the MTDFREML application, which uses the methodology of the Restricted Maximum Likelihood Derivative Free with an animal model that considers as fixed the effects of the farm such as year, month of birth, and gender. The heredity for P205 was 0.13 ± 0.02 and for P365 was 0.18 ± 0.05, which may indicate little additional genetic variation for these characteristics. For P550 days the estimated heredity was 0.23 ± 0.07, considered average, what indicates that at this age it is possible to select for weight gain. The genetic, phenotypical and environmental likeness among the weights in different ages were- P205-P365 = 0.92, 0.72 and 0.79; P205-P550 = 0.89, 0.61 and 0.87 and P365-550 = 0.98, 0.80 and 0.87. The genetic tendency in P365, for direct effect was significant and positive equals 0.455 kg (P < 0.001). Genetic trends in P205, P365 and P550 for direct effect were significant and positive, equal to 0.272 kg (P < 0.001), 0.455 kg (P < 0.001) and 0.744 kg (P < 0.001), respectively.