Investigation of genotype x environment interactions for weaning weight for Herefords in three countries

The objective of this study was to investigate the possibility of genotype X environment interactions for weaning weight (WWT) between different regio ns of the United States (US) and between Canada (CA), Uruguay (UY), and US for populations of Hereford cattle. Original data were composed of 487,661, 102,986, and 2,322,722 edited weaning weight records from CA, UY, and US, respectively. A total of 359 sires were identified as having progeny across all three countries; 240 of them had at least one progeny with a record in each environment. The data sets within each country were reduced by retain ing records from herds with more than 500 WWT records, with an average cont emporary group size of greater than nine animals, and that contained WWT re cords from progeny or maternal grand-progeny of the across-country sires. D ata sets within each country were further reduced by randomly selecting amo ng remaining herds. Four regions within US were defined: Upper Plains (UP), Cornbelt (CB), South (S), and Gulf Coast (GC). Similar sampling criteria a nd common international sires were used to form the within-US regional data sets. A pairwise analysis was done between countries and regions within US (UP-CB vs S-GC, UP vs CB, and S vs GC) for the estimation of (co)variance components and genetic correlation between environments. An accelerated EM- REML algorithm and a multiple-trait animal model that considered WWT as a d ifferent trait in each environment were used to estimate parameters in each pairwise analysis. Direct and maternal (in parentheses) estimated genetic correlations for CA vs UY, CA vs US, US vs UY, UP-CB vs S-GC, UP vs CB, and S vs GC were .88 (.84), .86 (.82), .90 (.85), .88 (.87), .88 (.84), and .8 7 (.85), respectively. The general absence of genotype X country interactio ns observed in this study, together with a prior study that showed the simi larity of genetic and environmental parameters across the three countries, strongly indicates that a joint WWT genetic evaluation for Hereford cattle could be conducted using a model that treated the information from CA, UY, and US as a single population using single population-wide genetic paramete rs.