Relationship of Somatic Cell Score and Linear Type Trait Evaluations of Holstein Sires

Genetic evaluations of Holstein bulls for mean somatic cell score were compared with their standardized transmitting abilities for linear type traits. Based on first lactation daughter information from five dairy records processing centers, PTA for somatic cell scores for 712 sires ranged from –.50 to .56. Standardized transmitting abilities for 14 type traits were provided for these bulls by the Holstein Association. Mean transmitting abilities for udder traits were negative for the 100 bulls with highest PTA and positive for the 100 bulls with lowest PTA for somatic cell score. For all bulls, correlations of PTA for somatic cell score with udder trait evaluations were negative (–.31 for fore udder attachment, –.28 for udder depth, –.21 for front teat placement, –.17 for rear udder width, –.16 for udder cleft, and –.13 for rear udder height). The best five-trait model to predict PTA for somatic cell score consisted of transmitting abilities for fore udder attachment, thurl width, strength, dairy form, and body depth (R² = .142). If PTA for milk yield was included with evaluations for type traits, it replaced dairy form in the model. Inclusion of quadratic terms did not contribute greatly to prediction of PTA for somatic cell score. Selection for higher, more firmly attached udders should contribute to reducing somatic cell scores.