International comparison of Holstein Friesian dairy sires proven in Italy, Canada and the US

Holstein Friesian sires used in Italy were evaluated for milk, fat and fat% with a Maternal grandsire model to account for non-random mating, based on 391,286 first lactation records of daughters and grandaughters of 33,186 sires. Bulls imported from Canada and the USA were 18% of all sires used in natural service (NS) and artificial insemination (AI), sired 30% of the cows, and their ETA's were, on average, 95 kg for milk, 3.79 kg for fat and 0.007% for fat% higher than proofs of Italian born bulls.;Conversion factors between Canada, the USA and Italy were computed using a linear regression accounting for proofs' accuracy, based on 178 sires proven in Italy and Canada, and 162 proven in Italy and the USA, with repeatibility higher or equal to 0.70. Estimated differences between country genetic bases were 319 kg for milk, 13.7 kg for fat, and 0.05% for fat% for Italy over Canada, and were 524 kg, 19.1 kg and 0.01% for Italy over USA. Regression coefficients of Italian on Canadian, and of Italian on US proofs were 27.3 and 0.279 for milk, 0.953 and 0.281 for fat, and 0.64 and 0.800 for fat%. Correlations between converted and actual proofs were between 0.78 and 0.88.;Canadian and USDA official proofs (from Spring and January 1985 respectively) for milk, fat and fat% of Holstein sires with at least 20 daughters were pooled with those estimated for Italy using the MGS model. Proofs of 1766 sires proven in Canada, 9746 in the USA and 4191 in Italy were deregressed and a linear model which included country of proof, genetic group of sire, and sire within group effect, was used to estimate international sire ETA's. The relationship matrix of sires was included.;Differences from the country solutions in Italy were, for Canada and the USA respectively, 334 and 565 kg for milk, 14.38 and 19.57 kg for fat, and 0.047 and $-0.005$% for fat%. Average international proofs (IP) of sires born between 1955 and 1979 were, in Canada, the USA and Italy respectively: 84, 272 and 2 kg for milk, 3.65, 9.01 and 0.46 kg for fat, and 0.012, $-0.013$ and 0.006% for fat%. Genetic changes of sires born between 1964 and 1979 were 174, 268 and 99 kg for milk, 7.72, 7.97 and 3.30 kg for fat, and 0.030, $-0.030$ and 0.060% for fat% in Canada, the USA and Italy. Imported sires comprising 18%, 3% and 25% of all sires proven in Canada, the USA, and Italy, were respectively 126, $-211$ and 45 kg for milk, 4.15, $-6.44$ and 1.97 kg for fat, and $-0.006,$ 0.022 and 0.006% for fat% different from local sires. The highest selection differential for sires of bulls was in Canada.