Effects of sex and age on genotype x environment interaction for beef cattle body weight studied using reaction norm models.

The interest in the effect of genotype by environment interaction (GEI) is increasing because animal breeding programs have become geographically broader. Climate changes in the next decades are also expected to challenge the present breeding goals, increasing the importance of environmental sensitivity. The aim of this work was to analyze GEI effect on cattle weight using the environmental sensitivity predicted by random regression reaction norm models, including sex and age effects as additional dimensions in the study. Genetic parameters were estimated for adjusted weights of Brazilian Nelore cattle at different ages (120, 210, 365 and 450 days), using linear polynomials for random regression analysis. The analyses with sex as a fixed effect (total analyses TA) were compared to those with sex-separated progenies (male and female progeny analyses – MPA and FPA, respectively). (Co)variance components were estimated and breeding values calculated as expected progeny differences (EPDs). The results showed important differences in reaction norm model genetic parameter estimates according to different age and sex analyses. They confirmed the presence of an important genotype by environment by sex by age interaction for Nelore cattle weight. The patterns in these results lead to a revision of the importance of sexual and developmental factors on plasticity and adaptation concepts. Key-words: cattle, environmental sensitivity, genotype by environment interaction, reaction norm, sex effect, weight INTRODUCTION Reaction norm (RN) was defined by Schmalhausen (1949) as the set of phenotypes that can be produced by an individual genotype exposed to different environmental conditions. The introduction of random regression models (RRM) in longitudinal data studies (Kirkpatrick and at Sistema Integrado de Bibliotecas daUSP on September 30, 2011 jas.fass.org Downloaded from