652. Reaction Norm Models Contribute to the Investigation of Environmental Sensitivity for Weaning Weight in Nellore Cattle

Reaction norm models (RNM) can be used to assess environmental sensitivity of animals for traits affected by genotype by environment interaction. Three RNM were tested for weaning weight (WW) in Nellore cattle. Phenotypic data from 772,855 animals were obtained from the Aliança Nelore dataset. The best model, according to the AIC criteria, was a spline linear-linear heteroscedastic RNM. Results suggest existence of a non-linear component in the reaction norm of WW and that the slope of the first and second segments are highly and negatively correlated. For animals selected in the low environment gradient (EG), the EBV average decreased in the medium and high EG. Trajectories along the EG when animals were selected in the medium and high gradients were similar. To reduce animal sensitivity to environmental variation, the selection could be based on genetic performance and environmental sensitivity, which can lead to a better genetic response for all EG.