Genetic Relationships and Linear Model Comparisons Between United States and Canadian Ayrshire and Jersey Bull Populations

The ties and relationships within the Ayrshire and Jersey bull populations from the United States and Canada were investigated. Twenty-two percent of genes in the United States Ayrshire bull population were of Canadian origin, whereas 22% of genes in the Canadian Jersey bull population were of United States origin. Average genetic relationships among bulls between countries were comparable with the within country relationships. The BLUP animal model bull proofs for milk and fat production from each bull’s country of evaluation were subsequently used to rank bulls across countries with a linear model. Genetic differences, differences in reference bases, and relative genetic progress in the various bull populations were also estimated. On the average in the last 20 yr the United States and Canada have produced and evaluated Ayrshire bulls of equal genetic merit for milk and fat, but the United States has produced and evaluated better Jersey bulls than Canada by .7 SD of milk and .6 SD of fat. The rate of genetic progress for either trait over that time, however, was similar in both countries and both breeds and ranged from .07 to .09 SD/yr. Across country proofs by the linear model were highly correlated with domestic animal model proofs and converted foreign proofs. (