Genetic Correlations Among Somatic Cell Scores, Productive Life, and Type Traits from the United States and Udder Health Measures from Denmark and Sweden

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Abstract
Sire genetic evaluations for protein yield, somatic cell score (SCS), productive life, and udder type traits from the US were correlated with sire evaluations for udder health from Denmark and Sweden and then the correlations were adjusted for accuracies to approximate genetic correlations. Traits from Denmark and Sweden included somatic cell count (SCC) and clinical mastitis from single-trait analyses. In addition, evaluations for clinical mastitis from Denmark and Sweden were regressed on US traits to test for quadratic relationships. Information from 85 bulls with US and Danish evaluations (77 with US type) and from 80 bulls with US and Swedish evaluations (79 with US type) was used to calculate correlations. Genetic correlations of US protein yield with Danish and Swedish SCC and clinical mastitis were all unfavorable (-0.09 to -0.32). Genetic correlations of US productive life with Danish and Swedish SCC and clinical mastitis were all favorable (0.06 to 0.59). Genetic correlations between US SCS and Danish SCC and between US SCS and Swedish SCC were -0.87 and -0.99, respectively (favorable). Genetic correlations between US SCS and Danish clinical mastitis and between US SCS and Swedish clinical mastitis were -0.66 and -0.49, respectively (favorable). The US type traits that had the largest correlations with clinical mastitis from Denmark and Sweden, respectively, were udder composite (0.26, 0.47), udder depth (0.45, 0.52), and fore udder attachment (0.31, 0.34). In general, quadratic regressions indicated little nonlinearity between clinical mastitis and the US traits. Specifically, the US bulls with the lowest predicted transmitting abilities for SCS had the most favorable rates of daughter clinical mastitis in Denmark and Sweden. Selection for increased productive life, lower SCS, and more shallow udders should improve mastitis resistance.