A case-control study of lameness in dairy cows

A case-control study was conducted to compare the physical hoof properties of digits responsible for clinical lameness with those of other digits on the same cows and with those of equivalent digits on non-lame control cows. The control cows were herd-mates matched by age, breed and stage of lactation. Hoof moisture, hoof hardness and sole concavity were measured on-farm. The resilience, compressive strength and elastic modulus of both sole and wall hoof were measured on biopsy samples collected from both case and control digits. White line disease, sole bruising and septic pododermatitis accounted for 92% of the clinical lameness lesions in the case digits examined. Less severe forms of white line disease and hoof haemorrhage were also observed frequently in the non-lame digits of both the case and control cows. Independent variables were screened for unconditional associations with case-control status using Student's paired t-test and Wilcoxon's matched pairs test. Conditional logistic regression analysis was finally used to identify which risk factors were associated with lameness. When equivalent digits on the matched cows were used as controls, sole and heel moisture, sole hardness, sole concavity and wall colour were selected for inclusion in the model derived to explain differences between the physical properties of lame and control digits. Values for each of these properties were lower in the lame digits than in the controls. The control digits had a higher percentage of black coloration than the lame digits. Sole hardness and sole concavity (both lower in the lame digits) were also selected for inclusion in the conditional logistic regression model derived when the adjoining digits on the same legs of the lame cows were used as controls. None of the physical hoof properties measured were associated with lameness when attempts were made to fit a model using the equivalent digits on the opposite legs of the lame cows as controls. Production of the lame cows was also compared with that of matched herd-mates. Total lactation yields of milk, milk fat and milk protein were lower for the lame cows than for the control cows (P<0.05).