Journal of Dairy Science, Vol 75, Issue 4 1138-1146, Copyright
© 1992 by American Dairy Science Association
Direct and indirect conversion of bull evaluations for yield traits between
countries
R. L. Powell and M. Sieber
Animal
Improvement Programs Laboratory, Agricultural Research Service, USDA Beltsville,
MD 20705-2350.
Genetic evaluations of Holstein bulls from the US were matched with
Canadian, Italian, Mexican, and Netherlands evaluations for the same
bulls. Conversion equations for milk yield were computed by least
squares, Goddard, and Wilmink methods. Accuracy was assessed by
splitting data and applying equations developed from one subset to
the other subset. Methods were judged by mean differences between
actual and converted evaluations and standard deviation of that
difference. Imperfection of conversions appeared to be due to
inherent characteristics (variation and bias) of data rather than to
inadequacy of conversion methodology. Least squares was slightly
better than other methods but is not recommended by the International
Bull Evaluation Service. The Goddard method was generally superior to
the Wilmink method, but data often are not available for its
application. A variation of the Goddard method was equal in accuracy to
the Wilmink method. Daughter yield deviation as both dependent and
independent variables was examined for only one data set and was
little different from the Goddard method. Indirect equations were
quite accurate for US to Mexico and US to the Netherlands but much
less accurate for US to Italy conversion. Indirect conversions still
would be useful until evaluations of bulls in common allow for direct
conversions. For all three countries, a variation on indirect
methodology was slightly superior to the usual indirect equations.
