Threshold and linear bayesian models in the genetic parameters estimation for morphological traits in Nelore cattle

Abstract

It was aimed to compare the estimates of genetic parameters for body structure, finishing precocity and muscling obtained in single-trait and two-trait bayesian analyses under linear and threshold models. Visual scores obtained from 4,155 Nelore cattle at yearling, belonging to the Brazilian Nelore Program, were used. The animals were evaluated visually by method SAM (System of Morphologic Evaluation). Genetic parameters were estimated by single-trait bayesian analysis considering linear and threshold models (morphological traits) and two-trait bayesian analysis considering linear-linear and linear-threshold models (including the weight to the 120 days). In single-trait analysis, it was verified that heritability estimated were similar for both the models. When considering two-trait analysis, the heritability estimates obtained in the linear-linear model had presented greater magnitude than that in the linear-threshold model. However, the Spearman correlations among the breeding values for different models (linear or threshold and linear-linear or linear-threshold) showed low alteration in the placement of the animals, and it was an insufficient modification to alter their classification as for the percentile, in other words, all the animals TOP1%, when linear models were used, continued being TOP1% when used threshold models. In the genetic evaluation of animals for morphological traits, the linear or threshold model can be used in genetic improvement programs.