Parámetros genéticos de pesos al nacer y al destete en ovinos de raza criolla de Chiapas Genetic parameters for birth and weaning weights in the local Chiapas sheep breed from Mexico

Variance components and heritabilities for birth (BW) and weaning weights (WW) were estimated in the local Chiapas sheep breed using data from animals born between 1991 and 2006. The pedigree contained 53 rams, 523 ewes, and 1,326 lambs. Six models were compared to estimate heritabilities of BW and WW using the difference ( i ) between the ith model and the best model from the Akaike information criterion (AIC). Model 1 contained additive genetic effects. Model 2 was as Model 1 plus permanent maternal environmental effects. Models 3 and 4 were as Model 1 plus maternal effects with cov(direct, maternal) equal to zero 0 for Model 3 and equal to am for Model 4. Models 5 and 6 were as Models 3 and 4 plus permanent environmental effects. Fixed effects of year, type and number of birth and sex were included in all models for both traits. Age at weaning was added as covariate for WW models. Model 6 was preferred for both traits because it accounted for direct and maternal effects and their correlation as well as maternal permanent environmental effects and the criteria for comparison were the smallest. Direct and maternal heritability as well as the permanent maternal environment estimates were 0.15±0.09, 0.24±0.09, 0.11±0.08 for BW and 0.14± 0.09, 0.09±0.08, 0.08±0.06 for WW, respectively, and the phenotypic (0.34±0.03) and genetic (0.81±0.18) correlation from model 6. These are the first estimates of genetic parameters for BW and WW in the Chiapas sheep breed.