Multiple-country comparison of dairy sires.

A multiple-trait sire model was described in which yields of daughters in different countries were considered to be different traits. Such a model required estimates of genetic correlations among sire genetic effects in different countries. Observations were average daughter yield deviations, which were yields adjusted for all fixed effects within a country and for mate and animal permanent environmental effects. The methodology was described through a small example. Methods for estimating genetic covariances between countries as well as the advantages and disadvantages of the multiple-country approach to international comparisons were discussed. The proposed method appears to be better theoretically than methods in which the genetic correlations among countries are assumed to be 1. The relationships of estimated transmitting abilities of sires from the multiple-country analysis with international conversion formulas were discussed.