Repeatability of objective measurements on the rear legs of dairy cows

The objective of this paper was to estimate the repeatability of objective measurements on the rear legs of dairy cows to see whether higher repeatability estimates could be obtained compared to the corresponding subjective linear score. Between September and November 1998, seven measurements of distance among dewclaw, hip, hock, pinbone, and thurl were taken on 73 cows from the University of Illinois dairy farm. Measurements were combined to define triangles and therefore angles reflecting rear leg structure. Three novice evaluators participated in the experiment, and, on a given day, two sets of measurements were taken by two evaluators. Cows were measured twice at a 1- to 4-wk interval. Size, evaluator, and order of measurement were included in the model as fixed effects. Cow, interactions of cow x evaluator and cow x order of measurement were random effects included in the model. The model explained over 80% of the variation for each variable. Repeatability estimates of the length measurements ranged from 0.61 to 0.89. Repeatability estimates of angles were much lower ranging from 0.00 to 0.24. The variation in natural standing position of the cow hampered the accuracy of the objective measurements. Low estimates of repeatability for angles describing rear leg suggested that objective measurements by novice evaluators were not sufficiently reliable to potentially replace the subjective linear score for rear leg curvature determined by experts. Usefulness of further investigation to find objective measurements that would give a better description of rear legs conformation compared to the corresponding current type trait was questionable.