Reaction norms in weights at 365 days old in nellore bulls in northern Brazil

Abstract

Genotype by environment interaction (GxE) studies are of particular interest in Brazil because of the regional diversity of environmental effects and the wide variety of management systems. The present study evaluates GxE effects on 365 d weight (365W) of Nellore cattle raised on pasture in northern Brazil. The analysis utilized random regression techniques to model the reaction norm. Fixed effects consisted of sex, contemporary group, and the covariate of age of cow at calving. The environmental gradient, defined by the concatenation of a bull and the state in which the calf was born, was modelled by second order Legendre polynomials. Direct additive genetic and residual effects were fit as random. Results showed differences in the magnitude of expression of genotype in proportion to decreasing favorability of the environment. As the environment became more unfavorable, the correlation of breeding value to different environments decreased. The correlations between the intercept and the level slope for 365W feature were of moderate magnitude, predominantly indicating the reclassification of sires in different environments. Reaction standard model was coherent from a technical and biological view point and enabled the perception of GxE in the genetic evaluation of Nellore cattle in the states of Maranhão, Pará and Tocantins. Key words: Animal breeding, growth, random regression ResumoNo Brasil, estudos de interações genótipo x ambiente tem atraído cada vez mais atenção em programas de melhoramento devido à variedade de sistemas de produção e à diversidade ambiental. Objetivou-se avaliar o efeito da interação genótipo x ambiente sobre o peso ajustado aos 365 dias de idade de bovinos da raça Nelore criados a pasto na região norte do Brasil. As análises foram realizadas utilizando-se regressão aleatória para modelar a norma de reação. Foi considerado como efeitos fixos o sexo, os

How herd best linear unbiased estimates affect the progress achievable from gains in additive and nonadditive genetic merit

“…The differential in genetic standard deviations and the regression coefficients of the phenotypic performance on the respective EBV by environment is not novel and has been reported elsewhere in dairy cattle (Craig et al, 2018), beef cattle (Ferreira et al, 2015), and sheep (Pollott and Greeff, 2004). The novelty here, however, was that no study to date has stratified environments based on BLUE and therefore there was an implicit link between the herd stratum for the performance trait and genetic merit because the mean genetic merit of the herds would have contributed to their eventual phenotypic performance; this is especially true for highly heritable traits such as milk yield.…”

“…Moreover, the expectation is that a 1 unit difference in EBV should equate to a 1 unit difference in performance (in the average environment). The existence of genotype by environment (G × E) interactions contributes to a deviation from the expectation and such deviations have been documented in dairy cattle (Craig et al, 2018), beef cattle (Ferreira et al, 2015), and sheep (Pollott and Greeff, 2004). Previous studies, however, stratified herds based on performance, which implicitly encapsulates the total genetic merit of the contributing animals.…”