Multiple-breed reaction norm animal model accounting for robustness and heteroskedastic in a Nelore–Angus crossed population

Abstract

Our objective was to genetically characterize post-weaning weight gain (PWG), over a 345-day period after weaning, of Brangus-Ibagé (Nelore × Angus) cattle. Records (n = 4016) were from the foundation herd of the Embrapa South Livestock Center. A Bayesian approach was used to assess genotype by environment (G × E) interaction and to identify a suitable model for the estimation of genetic parameters and use in genetic evaluation. A robust and heteroscedastic reaction norm multiple-breed animal model was proposed. The model accounted for heterogeneity of residual variance associated with effects of breed, heterozygosity, sex and contemporary group; and was robust with respect to outliers. Additive genetic effects were modeled for the intercept and slope of a reaction norm to changes in the environmental gradient. Inference was based on Monte Carlo Markov Chain of 110 000 cycles, after 10 000 cycles of burn-in. Bayesian model choice criteria indicated the proposed model was superior to simpler sub-models that did not account for G × E interaction, multiple-breed structure, robustness and heteroscedasticity. We conclude that, for the Brangus-Ibagé population, these factors should be jointly accounted for in genetic evaluation of PWG. Heritability estimates increased proportionally with improvement in the environmental conditions gradient. Therefore, an increased proportion of differences in performance among animals were explained by genetic factors rather than environmental factors as rearing conditions improved. As a consequence response to selection may be increased in favorable environments.

Genomic reaction norm models exploiting genotype × environment interaction on sexual precocity indicator traits in Nellore cattle

“…However, the genetic correlation between intercept and slope was positive and of high magnitude for both traits, indicating that animals with higher intercept (average breeding value) respond more when the environmental conditions become less restrictive. Some studies indicated that a high correlation between intercept and slope suggests the occurrence of animals re‐ranking when evaluated in different environments (Su et al ; Oliveira et al ; Zhang et al ). Oliveira et al () observed that this occurs by scale effect in the EBV.…”

“…Some studies indicated that a high correlation between intercept and slope suggests the occurrence of animals re-ranking when evaluated in different environments (Su et al 2006;Oliveira et al 2016;Zhang et al 2019). Oliveira et al (2016) observed that this occurs by scale effect in the EBV. The correlation estimate between intercept and slope was similar to that observed by Santana et al (2018) in Nellore cattle for HP (0.65) and higher than those reported by Santana et al (2013Santana et al ( , 2015 for SC of 0.001 and 0.14 respectively.…”