Comparison of animal models for estimation of (co)variance components and genetic parameters of reproductive, growth and slaughter traits of Californian and New Zealand rabbits raised under tropical conditions

In order to compare different animal models, the methodology of mixed models under animal models was used to predict (co)variance components of 23 traits related to reproduction traits of 1,456 litters and growth and slaughter traits of 3,845 Californian and New Zealand White rabbits raised in south-eastern Brazil. The (Co)variance components, obtained by four different models in single trait analysis, were used to estimate genetic parameters. The four animal models considered as random effects only the animal direct genetic effects (model 1), the animal direct and permanent effects of litters or common effects of does as permanent environment effects(model 2), the animal direct and maternal genetic effects, uncorrelated to each other, and permanent environmental effects (model 3), and as in model 3, but with correlated animal direct and maternal effects (model 4). All the model considered the fixed effects of contemporary groups, parity, sex and the covariates level of inbreeding of litters or rabbits and litter sizes, where applied. The models were compared based on likelihood ratio test and the "best" model is proposed for each trait. Permanent environmental effects were important for all traits and should be considered in animal models that analyse reproductive, growth and slaughter traits of rabbits of these two breeds. Maternal genetic effects were not important to reproductive traits, but significantly affected growth and slaughter traits, and were more important for New Zealand White than for Californian rabbits. As models 1,2,3 and 4 gave different estimates for genetic parameters, total heritabilities were calculated for all traits. Total heritabilities were low for reproductive traits (from 0 to .14), and moderate for growth (from .03 to .36) and slaughter traits (.02 to .23). Although New Zealand White and Californian rabbits perform similarly, the results showed that the genetic parameters for these two breeds are different and should not be analyzed together. The models chosen for each trait serve as guides for proposition of animal models in single or multi trait analysis of rabbit data.