| Records from the Hereford Associations of USA, Canada and Uruguay were utilized to obtain genetic and phenotypic (co)variances for weaning weight (WWT) to determine if genetic parameters for WWT were homogeneous across environments and to investigate the possibility of genotype by environment interactions between different regions of USA and between USA, Canada (CAN) and Uruguay (URU). Four regions within US were defined, Upper Plains (UPP), Cornbelt (CB), South (S) and Gulf Coast (GC) as being representative of distinct environments. A total of 359 sires were identified that had progeny, grandprogeny or great grandprogeny with records across all three countries. Of these 359 sires, 240 had at least one progeny with a record in each country. Only herds with records from progeny or maternal grandprogeny of the 359 sires were utilized. A pair wise analysis was done between countries and regions within USA (UPP-CB versus S-GC; UPP versus CB and S versus GC) fitting a multiple-trait animal model considering WWT as a different trait in each region or country. Breeding values were estimated for North America (NA), URU and joint data from NA and URU (JT). Direct (maternal) heritability estimates were 0.24 (0.16), 0.20 (0.16) and 0.23 (0.18) for US, Canada and Uruguay, respectively. Covariance between direct and maternal was negative in all countries, accounting for 6, 8 and 10% of the total phenotypic variation, while total dam effect was 32.5, 37.0 and 34.0% in USA, Canada and Uruguay, respectively. The genetic correlation estimates for direct (maternal) genetic effects were 0.86 (0.82), 0.90 (0.85) and 0.88 (0.84) for the USA-CAN, USA-URU and CAN-URU analyses, respectively. For the across regions within USA analyses, the same estimates were 0.88 (0.87), 0.88 (0.84) and 0.87 (0.85), for UPP-CB vs. S-GC, UPP vs. CB and S vs. GC, respectively. Rank correlations were 0.99 and 0.98 between direct and maternal breeding values, respectively, in the NA and JT analyses, while between the URU and JT analyses the same rank correlations were 0.90 and 0.87. Results of this study would strongly suggest that a joint genetic evaluation for Herefords could be conducted treating NA and URU as a single population, using single population-wide genetic parameters. |
