Progeny Tests of Sires in the United States and in Mexico

Sire summaries were calculated from records of 14,054 Mexican Holstein cows. Of 265 bulls with 10 or more daughters in Mexico, 142 United States and Canadian bulls also had summaries in the United States. Correlations and regressions between these independent proofs showed no interaction between sire and country. The genetic correlation was 1.006. Predicted Differences in Mexico for milk yield of the 92 bulls from the United States averaged 79 kg higher than those of the 126 bulls from Canada and 204 kg higher than those of the 47 bulls from Mexico. Corresponding superiorities for bulls from the United States in Modified Contemporary Deviations were 184 and 341 kg. Cows imported into Mexico from the United States or Canada were superior to nonimported Holsteins; United States cows produced the highest. Mexican dairymen can make the most rapid genetic progress for milk yield by using superior germ plasm regardless of origin. Increased attention to the genetically superior bulls and cows available in the United States is warranted.