Locomotion ability of Holstein-Friesian genotypes under two grazing systems

Three genotypes of spring-calving Holstein-Friesian dairy cows (n=126) with respective average value (±SD) economic breeding index (EBI; Nov. 2005) of 30 (13.6), 70 (9.7) and 80 (18.67) were allocated to either a high concentrate (2.8 LU/ ha and 1,200 kg concentrate/cow/yr) or low concentrate (2.6 LU/ha and 500 kg concentrate/cow/yr) grass based feed system. Clinical lameness (CL) was recorded routinely and the effect of genotype or feed system on the logic of the probability of CL (CL=1 if lame within the first 200 days in milk, otherwise CL=0) was modelled using logistic regression. Locomotion ability (LA) was assessed fortnightly using 6 different gait aspects (spine curvature, speed, tracking, head carriage, abduction/ adduction and general symmetry). Each aspect was scored from 1 (not-lame) to 5 (severely lame). All gait aspects and as well as the average LA were set at a threshold of 4. The hazard of a cow reaching the threshold at day t post-calving, given that it had not reached the threshold by time t-1, was modelled using survival analysis. Incidence of CL was 25%. The EBI 30 genotype tended to have higher incidence of CL (P=0.09) and poorer LA (P=0.09) compared to the other genotypes. Feed system had no significant effect on CL although animals on the high concentrate feed system had a significantly greater hazard of poorer LA (hazard ratio = 3.05; 95% CI: 1.78 to 5.25). Of the different aspects of locomotion, spine curvature differed (P≤0.05) across genotypes. The EBI 70 and 80 genotypes exhibited a lower hazard of an inferior spine score than the EBI 30 genotype. This study indicates that selection for higher EBI will have no deleterious effect on LA or CL and actually may favour better locomotion. Nonetheless, being a short-term study, further measures across time are required to confirm these results.