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

Abstract

-The objective of this study was to evaluate the genotype-environment interaction (GEI) in the body weight adjusted to 550 days of age (W550) of Polled Nellore cattle raised in Northeastern Brazil using reaction norms (RN) models. Hierarchical RN models included fixed effects for age of cow (linear and quadratic) and random effects for contemporary groups (CG) and additive genetic RN level and slope. Four RN hierarchical models (RNHM) were used. The RNHM 2S uses the solutions of contemporary groups estimated by the standard animal model (AM) and considers them as environmental level for predicting the reaction norms and the RNHM 1S , which jointly estimate these two sets of unknowns. Two versions were considered for both models, one with a homogeneous (Hm) and another with a heterogeneous (He) residual variance. The one-step homogeneous residual variance model (RNHM 1S Hm) offered better adjustment to the data when compared with other models. For the RNHM 1S Hm model, estimates of additive genetic variance and heritability increased with environment improvement (260.75±75.80 kg 2 to 4298.39±356.56 kg 2 and 0.22±0.05 to 0.82±0.01, for low-and high-performance environments, respectively). High correlation (0.97±0.01) between the intercept and the slope of RN shows that animals with higher genetic values respond better to environment improvement. In the evaluation of breeding sires with higher genetic values in the various environments using Spearman's correlation, values between 0 and 0.98 were observed, pointing to high reclassification, especially among genetic values obtained by the animal model in comparison with those obtained via RNHM 1S Hm. The existence of GEI is confirmed, and so is the need for specific evaluations for low, medium and high level production environments.

Interação genótipo x ambiente via modelos de normas de reação para características de crescimento em bovinos Nelore

“…Em diversos estudos (Mattar et al, 2011;Ambrosini et al, 2014a;Ribeiro et al, 2015), observaram-se herdabilidades inferiores às estimativas de modelo animal padrão nos piores ambientes, mas com aumento em ambientes favoráveis. Provavelmente, este comportamento advém do fato de os indivíduos terem melhores condições de expressar o potencial de seus genótipos nos melhores ambientes.…”

“…No entanto, mesmo as correlações medianas podem levar a mudanças importantes na classificação dos reprodutores. Ambrosini et al (2014a) estudaram Nelore Mocho, e Corrêa et al (2010), a raça Devon, e relataram correlações similares, em que a maioria das alterações na classificação ocorreu entre o ambiente baixo e alto do gradiente ambiental (Santos et al, 2008).…”

“…Na realidade, um animal não conseguirá produzir sem um mínimo de condições necessárias, não importa quão robusto seja esse genótipo. Vários estudos com normas de reação com Nelore Mocho, Devon, Canchim e Angus (Corrêa et al, 2010;Mattar et al, 2011;Cardoso & Tempelman, 2012;Ambrosini et al, 2014aAmbrosini et al, , 2014b; e) têm mostrado que animais robustos tendem a ser menos produtivos e a apresentar baixa amplitude de valores genéticos no gradiente ambiental.…”

“…Em trabalho anterior, avaliou-se a interação genótipo x ambiente, em modelo de normas de reação, quanto à características de crescimento na raça Nelore Mocho (Ambrosini et al, 2014a(Ambrosini et al, , 2014b. Os materiais genéticos empregados no presente estudo e nos anteriores são diferentes.…”

Seasonal sensitivity of genotypes in the humid tropics and its application to chicken breeding

“…Recently, studies were performed on genotypeenvironment interaction for body weight adjusted to 205 days (Ambrosini et al, 2014b), for body weight adjusted to 550 days of age (Ambrosini et al, 2014a) and for weaning weight (Ribeiro et al, 2015) in Polled Nellore cattle. They showed in their reports that animals with higher genetic values respond better to environmental improvement.…”