Genotype-environment interaction between Chile and North America and between Chilean herd environmental categories for milk yield traits in Black and White cattle

In order to evaluate the expression of sire genetic evaluations obtained in North America for Chilean Black and White Cattle, genetic correlations were estimated for milk (MY), fat (FY) and protein (PY) yields, and for fat (F%) and protein (P%) contents between Chile, Canada and the US, from predicted transmitting abilities of common sires in two countries. Moreover, genetic correlations for the same traits were estimated between herd environmental categories formed according to MY levels, using bivariate analyses. Genetic correlation estimates for MY, FY, and PY between Chile-Canada (0.80, 0.61, and 0.70), and between Chile-US (0.79, 0.68, and 0.77), were lower than values obtained by simulation, assuming sire selection of the best 50%, and were also lower than the genetic correlations between Canada-USA, which were close to 1, suggesting a moderate genotype by country interaction. All genetic correlation estimates between countries for F% and P% were close to 1. No evidence of genotype-environment interaction was found for any trait between High and Low Chilean herd environmental categories based on MY, (genetic correlation estimates >= 0.96; not statistically different from 1). Results indicate that a single national dairy genetic improvement programme incorporating international evaluations could be implemented in southern Chile, rather than separate programmes for specific herd MY environments. Moderate genotype-environmental interaction between North American and Chilean environments was found for MY, FY, and PY. Results from across and within country analyses indicate that sire selection in North America for milk solids yield will produce relatively high correlated genetic responses for the southern Chile dairy production system characterized by grazing and a temperate climate.