A method for combining United States and Canadian bull evaluations.

Canadian and US genetic evaluations for July 1991 were combined for 3304 Holstein bulls evaluated in Canada that had US progeny or a cross-reference code. Canadian evaluations of the bulls and their sires and dams were converted to US PTA. Combined PTA were weighted averages of progeny information from both countries and parent average. Parent average was recomputed from the sire's combined evaluation and the dam's evaluation with the most daughter equivalents. Bulls were processed in birth year order so that combined evaluation of sire was available. Progeny contribution was adjusted to remove the influence of the bull's evaluation on progeny evaluations through their parent averages, which left only the portion that was due to progeny records and grandprogeny information. A weighted average of adjusted progeny contributions was combined with parent average to form a combined PTA more accurately than possible by averaging domestic and converted PTA. Combined reliability was computed by summing daughter equivalents from progeny and from updated evaluations of parents. Canadian daughter equivalents were multiplied by .9 to approximate US values. Combined evaluations simplify bull selection by providing comparable and complete information for bulls evaluated in two countries.