Journal of Dairy Science, Vol 75, Issue 10 2834-2839, Copyright
© 1992 by American Dairy Science Association
A method for combining United States and Canadian bull evaluations
G. R. Wiggans, P. M. VanRaden and R. L. Powell
Animal Improvement Programs Laboratory, Agricultural Research Service,
Beltsville, MD 20705-2350.
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.
