Genetic analysis of locomotion and associated conformation traits of Holstein-Friesian dairy cows managed in different housing systems.

The objectives of this study were to determine the influence of housing on lameness-related linear and composite traits, and to estimate heritabilities of the traits and correlations among them. Data comprised 156,770 national type evaluation records of pedigreed first-lactation Holstein-Friesian cows that calved from 2000 through 2006 and were classified in different housing systems--cubicles, straw yards, slatted or loafing yards, and on pasture. Locomotion score (LOCO), rear leg, side view (RLS), foot angle (FA), bone quality (BO-NEQ), legs and feet (L&F), and mammary composite (MAMM) were the traits measured. Data were analyzed by REML, using an animal model. In general, cows in grazing systems had better locomotion, straighter RLS, steeper FA, flat and more refined bones, better L&F, and better mammary systems compared with cows housed in other systems. Estimates of heritability ranged from 0.11 for LOCO to 0.31 for MAMM. Bone quality had the highest heritability (0.23) of the traits associated with L&F. Genetic associations between BO-NEQ and LOCO, L&F, and MAMM were moderate to high (0.30 to 0.50), but estimates between BONEQ and RLS and FA were not significantly different from zero. Locomotion score had a very high genetic (0.98) and phenotypic (0.78) correlation with L&F, indicating that both traits are genetically the same. On the basis of the genetic parameters, including BONEQ in a selection index as a predictor of longevity is promising, but further information on its association with longevity is required.