GxE

Genotype-by-Environment Interaction for Weaning Weight in Angus Cattle Using Principal Component and Multi-dimensional Reaction Norm Analysis

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Abstract

In the U.S., beef cattle are raised across diverse environmental conditions with varying management practices, leading to potential genotype-by-environment interactions (GEI), which can be an important source of phenotypic variation in growth traits. The present study aimed to investigate the presence and magnitude of GEI for weaning weight (WW) in Angus cattle based on reaction norm model (RNM) analyses. The dataset comprised about 1.19 million WW records (mean ± SD: 287.040 ± 42.320 kg) of purebred Angus cattle registered with the American Angus Association. Two analytical approaches were considered. In the first approach, the contemporary group (CG) solutions of WW obtained from an animal model were used as a proxy of herd environment gradient (EG) to assess GEI using single-dimensional RNM. The RNM included fixed effects of population mean and CG, and random direct additive genetic, maternal additive genetic, maternal permanent environmental, and residual effects, with reaction norms applied to the direct additive and maternal additive genetic components. In the second approach, the herd environment was described simultaneously by two principal components (PC1 and PC2 scores) constructed based on fifteen environmental variables that were standardized and used in a principal component analysis. The two PCs explained 56% of the total environmental variance and were used as EG in a multi-dimensional RNM (MRNM). With this methodology, each animal's estimated breeding value (EBV) is expressed as a response surface over the two environmental dimensions. Our study revealed heterogeneity in heritability and genetic variance estimates across PC scores of herd environments, suggesting the presence of GEI. Direct additive heritability estimates for WW were moderate and increased progressively toward positive PC1 and PC2 scores, ranging from 0.279 ± 0.012 to 0.495 ± 0.011, suggesting that greater response to selection for direct additive genetic effects can be achieved particularly in positive PC1-PC2 EG. We found slope variances for PC1 (0.55 ± 0.14 kg²) and PC2 (3.79 ± 0.280 kg²) scores for direct additive genetic effects - indicating GEI for WW in Angus cattle. Genetic correlation estimates across PC1-PC2 EG ranged from 0.65 to 0.99, indicating that selection at different points along the PC1-PC2 EG affect sire performance across environments. We also analyzed the reaction norms of the top 50 sires with the highest EBVs at the reference environment (PC1=PC2=0). Reaction norms of these sires further reinforced the existence of GEI across different levels of environmental PCs. Crossing of sire reaction norms occurred primarily along the PC2 gradient while PC1 was held constant, indicating a substantial rank-type GEI. Within this context, the MRNM allows the genetic prediction of an individual across a multi-dimensional range of environments facilitating the simultaneous selection of animals with high WW and environmental robustness, thereby enabling precision, environment-specific breeding and management decisions.

Keywords: 2026

How to Cite:

Sigdel, A., Heo, S., Garcia, A., Lourenco, D., Rowan, T., Brito, L., Gondro, C., Huang, J., de Souza, S., Retallick, K. & Rosa, G., (2026) “Genotype-by-Environment Interaction for Weaning Weight in Angus Cattle Using Principal Component and Multi-dimensional Reaction Norm Analysis”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286513. doi: https://doi.org/10.31274/wcgalp.24035

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