Evaluation of a lameness scoring system for dairy cows.

Lameness is a major problem in dairy production both in terms of reduced production and compromised animal welfare. A 5-point lameness scoring system was developed based on previously published systems, but optimized for use under field conditions. The scoring system included the words "in most cases" in the descriptions of the clinical signs evaluated. This was done to avoid a situation in which cows might not fit into any of the categories. Additionally, a number of clinical signs used in other lameness scoring systems, considered of less importance in relation to lameness, were not included. Only clinical signs were included that could easily be assessed within a few seconds from a distance. The scoring system was evaluated with intra-and interobserver agreement using kappa statistics. The evaluation was done before and after training 5 observers. Weighted kappa values ranged from 0.38 to 0.78 for intraobserver agreement, with mean kappa values across all observers of 0.60 and 0.53 before and after training, respectively. Weighted kappa values ranged from 0.24 to 0.68 for interobserver agreement, with mean kappa values across all pairs of observers of 0.48 and 0.52 before and after training, respectively. Training had only a limited positive effect on intra- and interobserver agreement. Additionally, how the different lameness categories are distributed along a theoretical scale representing the full spectrum of lameness from "absolutely normal gait" to "as lame as a cow can possibly be" was evaluated. This evaluation was done using the polychoric correlation coefficient. The estimated within-observer polychoric correlation coefficient ranged from 0.76 to 0.96, and there were no significant differences between the thresholds used to classify cows into different lameness categories by different observers before or after training. In conclusion, the results suggest that the lameness categories were not equidistant and the scoring system has reasonable reliability in terms of intra- and interobserver agreement.