Evaluation of maternal and individual heterosis on preweaning gain of Angus x Nellore calves

Records from 17,796 Angus x Nellore cattle out of 50 Associated Herds from the "Proaram Nature", in the states of Goias, Minas Gerais, Mato Grosso, Mato Grosso do Sul, Parana, Rio Grande do Sul, Sao Paulo and Tocantins were analyzed in order to estimate the effects of maternal and individual heterosis on the weight gain from birth to weaning. The used statistical model included the fixed effects of a general mean and contemporary groups, maternal and indivdual heterozygosity (covariables), random effects of sire (additive), dam (composite maternal), mendelian segregation and residue. To estimate the effects, an iterative process was used, that alternated genetic analysis for the contemporary groups and additive + maternal effects on the readjusted weight gain for heterosis and statistical analysis to estimate the effects of the covariables on readjusting weight gain for the contemporary groups and additive + maternal effects. The process was ended when the estimates became stable. The results indicated a positive linear relationship between heterozygosity and maternal and individual heterosis. Estimated values of 15.46% (22.62 kg) for maternal heterosis and 9.10% (13,31 kg) for individual heterosis were observed. Based on the degree of difficulties to estimate the heterosis effects in the present work, it is necessary caution to suggest just the inclusion of heterozygosities in the statistical model and let it be adjusted by itself.