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Genotype by environment interaction in Red Angus cattle in the United States
Genotype by environment interaction (GxE) can be defined as a reranking of genetic merit estimates of parents when progeny are produced in different environments. Increasing use of artificial insemination in the beef industry broadens the use of bulls across production environments. One approach to measuring GxE is to consider different production environments as separate traits and estimate genetic correlations between traits defined in this way. Previous researchers have suggested that a genetic correlation between environments of greater than 0.80 indicates little evidence of (GxE). The objective of this study was to estimate the magnitude of (GxE) interaction by estimating genetic correlations across production environments. Data for birth weight, weaning weight (n = 74,681), post-weaning gain (n = 39,104) and stayability (n = 28,895) were provided by the Red Angus Association of America. Records were assigned to nine regions: corn belt, desert, gulf coast, lower plains, mountains, northeast, pacific northwest, south and upper plains. To be included in the analysis, bulls had to produce at least 50 calves in at least two regions. Each region was considered a separate trait and genetic correlations were estimated by using ASReml. For the three growth traits there was no evidence of (GxE). Genetic correlations between pairs of regions were all 0.95 or greater. However, for stayability, genetic correlations were lower ranging from 0.24 (between the lower plains and pacific) to 0.86 (between the desert and upper plains.) Averaged across regions, the upper plains was mostly highly genetically correlated with other regions, with an average genetic correlation of 0.73, the average genetic correlation of the desert, gulf coast and south with other regions were intermediate, ranging from 0.57 to 0.60, and the lowest average genetic correlations ranged from 0.40 to 0.50 for the corn belt, lower plains, mountains, northeast, and pacific. In general, genetic correlations were highest between similar regions, mountains and upper plains, and hot regions including the desert, gulf and southeast. In conclusion, there is little evidence for G x E for growth traits, but stronger evidence for GxE exists for stayability suggesting that care should be taken when selecting sires to produce replacement heifers.
Keywords:
cattle, genotype by environment interaction, genetic correlation, stayability.