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* Interbull Centre, Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Box 7023, 750 07 Uppsala, Sweden
Department of Large Animal Sciences, The Royal Veterinarian and Agricultural University, Grønnegårdsvej 8, 1870 Frederiksberg C, Denmark
Beef Improvement Ontario, 660 Speedvale Ave. W., Suite 102, Guelph, Ontario N1K 1E5, Canada
Canadian Dairy Network, 150 Research Lane, Guelph, Ontario N1G 4T2, Canada
1 Corresponding author: thm{at}kvl.dk
International genetic bull evaluations of somatic cell counts (SCC) from 8 different Holstein populations and clinical mastitis from 3 of these populations were inferred simultaneously using a multiple-trait–multiple-country evaluation (MT-MACE) model. This model considered effective independent weighting factors and multivariately deregressed national genetic evaluations for countries with multiple-trait national models. Predictions of genetic merit from MT-MACE and their reliabilities were compared with the corresponding results from 2 separate single-trait–multiple-country evaluations (ST-MACE) for different groups of bulls. The assumed heritabilities for clinical mastitis (h2 = 0.02 to 0.05) were substantially lower than the heritabilities for SCC (h2 = 0.08 to 0.27). The predictive ability of MT-MACE was essentially equal to or better than the predictive ability of ST-MACE for all country-trait combinations, but both methods yielded effectively unbiased and consistent consecutive predictions (correlation > 0.93). Both sets of predictions also agreed well with future national genetic evaluations for bulls receiving additional daughter information (correlation > 0.96), except for evaluations for which within-country correlations were utilized internationally, but not nationally (correlation = 0.86 to 0.97). The reliabilities for MT-MACE were essentially equal to or higher than reliabilities for ST-MACE, depending on the trait and group of bulls in question. Reliabilities increased most for young bulls, and for clinical mastitis in countries that did not use the within-country correlations with SCC in the national evaluation (up to a 23% increase in average reliability).
Key Words: multiple trait • international genetic evaluation • clinical mastitis • somatic cell concentration
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