Caracterização da interação genótipo-ambiente e comparação entre modelos para ajuste do ganho pós-demama de bovinos Devon via normas de reação

Abstract

RESUMO -Os objetivos com este estudo foram verificar a presença de interação genótipo-ambiente e comparar modelos para o ajuste do ganho pós-desmama padronizado para 345 dias de bovinos da raça Devon, via normas de reação obtidas por regressão aleatória. Genotype by environment interaction characterization and model comparison for post weaning gain adjustment of Devon cattle via reaction normsABSTRACT -The objectives of this study were to verify the presence of the genotype by environment interaction and to compare different models to fit Devon cattle post weaning gain standardized to 345 days, via reaction norms obtained by random regression. Data from 14,973 calves collected by the beef cattle improvement program from 1980 to 2005 were used. The INTERGEN program was used for data analysis. First, a standard animal model (AM) was fitted to serve as comparison basis and to provide estimates of the environmental gradient, based on contemporary group (CG) deviations and, next, the reaction norms hierarchical models with homogeneous (RNHM) and heterogeneous (RNHMH) residual variances were run. In these last two models, fixed effects of age of dam and age of calf at yearling and random contemporary group and genetic effects (level and slope of animal's reaction norms) were included. For the RNHM estimates of residual variance, reaction norm level and slope additive genetic variances and their genetic correlation were, respectively, 272.02 ± 8.51; 340.38 ± 17.11; 0.119 ± 0.006 and 0.83 ± 0.01, while for the RNHHM were 401.96 ± 11.91; 177.86 ± 16.60; 0.076 ± 0.006 and 0.72 ± 0.02, respectively. The heritability asa well as the genetic variance increased on the environmental gradient, characterizing that there is genotype by environment interaction. Based on the Deviance Information Criterion, Bayes Factors and Pseudo Bayes Factors, the NRHM provided superior fit to the data, being the most appropriate model to consider the genotype by environmental interaction of this population.

Reaction norms models in the adjusted weight at 550 days of age for Polled Nellore cattle in Northeast Brazil

“…For the two-step model -the second best model -the correlations also displayed greater variation (−0.79 to 1.00), which denotes GEI. The results obtained herein indicate that the genetic material necessary for production in various environmental levels must be different, even if partially, and differ only in magnitude from those presented by Corrêa et al (2009), who observed the negative genetic correlations among environmental gradient levels for standardized post-weaning gain at 365 days. Mattar et al (2011) observed higher values than those in the present study (0.24 to 1.00).…”

Reaction norms for the study of genotype-environment interaction for growth and indicator traits of sexual precocity in Nellore cattle

“…The heritabilities found in those studies increased as the environment became more favorable (Fikse et al, 2003;Shariati et al, 2007;Corrêa et al, 2009;Pégolo et al, 2009;Strandberg et al, 2009). …”

“…Some studies have used reaction norm models to evaluate the presence of GxE effects (Corrêa et al, 2009;Pégolo et al, 2009). These norms describe the expression of a genotype as a linear function (reaction norm) of an environmental value or gradient.…”

Genetic evaluation of Devon Cattle using a reaction norms model

“…Recently, the existence of G*E interaction was verified in the Devon cattle population of Rio Grande do Sul State in Brazil (Corrêa et al, 2009). These authors observed that the reaction norms model with homogeneous residual variance was the best fit to the post-weaning gain data compared to the reaction norms model with heterogeneous residual variance and the animal model, traditionally used in genetic evaluations.…”