Genetic and Phenotypic Relationships between Clinical Mastitis, Laboratory Criteria, and Udder Height

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Abstract
Genetic aspects of mastitis resistance were investigated where quantitative scores were determined for clinical mastitis, bacterial infection, and leucocyte count. Heritability and repeatability estimates were obtained for these scores, and phenotypic and genetic correlations between scores were estimated. Correlations also were obtained between udder height and the scores for clinical mastitis, bacterial infection, and leucocyte count. The data for these estimates were from 682 lactations made by 422 cows in 4 state-owned dairy herds. Heritability estimates for clinical mastitis obtained from the paternal sister correlation and daughter-dam regression were inconsistent. Repeatability for clinical mastitis was estimated at .31. Estimated genetic correlations from the 2 analyses were .29 and .23 for clinical mastitis with bacterial infection, and .80 and .98 for clinical mastitis with leucocyte count. Udder height was negatively correlated with scores for clinical mastitis, bacterial infection, and leucocyte count.