IMPACT OF IMPORTED DAUGHTERS ON EVALUATIONS OF THEIR SIRES

Degree of bias in Modified Contemporary Comparison evaluations from including imported daughters was investigated to determine its impact on sire evaluation and subsequent development of conversion formulas between countries. Separate Modified Contemporary Deviations were computed from all daughters, only daughters with US dams, and only daughters with Canadian dams (daughters considered to be imported) for 31 Canadian Holstein bulls with a Repeatability of at least 40% in each subset. The deviations from daughters of Canadian dams were lower than those from daughters of US dams. Deviations weighted by product of Repeatabilities were significantly lower for both milk (113 kg) and fat (2.5 kg) for the subset of imported daughters. Lower evaluations for Canadian bulls did not affect conversion factors appreciably because 88% of daughters had US dams. However, demonstration of bias (apparently due to merit of mates) led to implementation of separate Canadian unknown-parent groups in animal model evaluations. For unknown dams of recently born cows, PTA for milk yield were about 250 kg lower for Canadian dams than for US dams. Daughter yield deviations averaged only 10 kg milk and .1 kg fat less for daughters of Canadian dams than for daughters of US dams. Correlations between subsets of daughters were near 1.