| Accuracy of sire selection is limited by how well animals are characterized. Current beef cattle genetic analyses ignore genotype by environment interactions (GxE). The objectives of this study were to evaluate the presence of GxE by comparing reaction norms of Red Angus bulls in the US. The dependent variables were birth weight, weaning weight, gain and stayability. Adjusted weights were provided by the Red Angus Association of America (RAAA). Gain was determined by subtracting adjusted weaning weight from adjusted yearling weight. Environments were defined as nine regions within the continental United States with similar temperature humidity index. The environmental mean was determined and a weighted regression was used to determine the progeny mean. Reaction norms were calculated by regressing the progeny mean on the environmental mean.;The objective of the weight study was to evaluate the genetic parameters for birth weight, weaning weight and gain. The range in reaction norms was the largest for BW and smallest for GN. The correlations of the trait mean to the trait RN was not significant for BW and WW but was for GN (P-value=0.02). The moderately negative (r=-0.22) correlation suggests bulls with higher means for GN have more stable production across environments.;The heritabilities of BW and WW RN were 0.40 and 0.39, respectively. Phenotypic and genotypic correlations were 0.19 and 0.54, respectively. These data suggest there is ample heritability for selection.;The objective of the stayability study was to evaluate the genetic parameters using a single-trait animal model for the regional and national datasets. A logit model was used to determine the heritability on the underlying scale. Heritabilities were 0.34, 0.18, 0.19, 0.08, 0.09, 0.28, 0.30, 0.31 and 0.40 for regions C, D, G, L, M, N, P, S and U, respectively and 0.18 for the national dataset. The percentages of females that calved at age four, given that they had calved at age two were 56.7, 39.9, 32.9, 51.1, 56.1, 57.0, 51.4, 47.8 and 58.8 for regions C, D, G, L, M, N, P, S and U, respectively and 55.0% for the national dataset. The Pearson correlation of the progeny mean to the RN was -0.196 (P-value <0.05) and suggest sires with higher means are more stable in their production across environments. The comparisons of regions illustrate the northern regions are more similar to each other compared to the southern regions and the southern regions are not only different from the northern regions but different from each other.;Reaction norms are heritable and there is sufficient variation for effective selection. Further research is warranted in the proper division of environments and the most economical and effective method to employ reaction norms to end-users. |
