Lameness continues to be a major welfare issue for dairy cows. In addition to the reduction in performance, the visual image of lame cows on farms can lead to a negative public perception of dairy farming. A survey in Minnesota found the prevalence of lame cows (those scoring a 3 or greater on a 1-to-5 scale) ranged from 3 to 50 percent on 53 farms.
Digital dermatitis, or hairy heel warts, is one of the most common, infectious disease causes of lameness. The typical method for evaluating cows for digital dermatitis requires putting the cow onto a hoof trimming table. While this method remains the “gold standard” for digital dermatitis as well as the other lesions and diseases that cause lameness, it’s labor-intensive and disruptive to the cow’s daily routine. For these reasons cows are evaluated infrequently.
It was hypothesized that cows could be routinely examined for digital dermatitis while in the milking parlor with minimal labor investment or disturbance to the cow. Two previous studies have attempted to establish methodologies that would allow for this type of noninvasive examination.
Unfortunately, neither study developed a protocol that would be practical in on-farm situations due to time (examinations took more than two minutes per cow) and equipment (relative cost) requirements.
Danish scientists from the University of Aarhus, the University of Copenhagen and Dyrlægerne Uni-Vet reported on their attempt to devise a practical method for the evaluation of digital dermatitis during milking. To address the shortcomings of previous work, these scientists evaluated a method that took no more than 15 seconds per cow and utilized no special equipment. The study was conducted on three commercial herds housed in freestall barns. To ensure a broad applicability, the three farms enrolled in the study used different parlor designs (herringbone, parallel and rotary). All lactating cows on each farm were examined in the parlor (day 1) and the trimming table (day 2).
The study found a large amount of variation in the sensitivity (observer recording a cow as positive for digital dermatitis that was confirmed as positive) and specificity (observer recording a cow as negative for digital dermatitis that was confirmed as negative). In general, the method used in this study was more successful at correctly determining cows that were not experiencing digital dermatitis. Sensitivity was greater for large (greater than 2 centimeter) lesions than small lesions (less than 2 centimeters); however, specificity was unaffected by lesion size.
Differences in sensitivity and specificity were found in the various types of parlors. The greatest sensitivity (0.84) was found for the herringbone parlor and the greatest specificity (0.97) was found in the rotary (the specificity of the parallel was 0.91).
The results of this study suggest that after appropriate training is provided (in this study the observer was trained by a veterinarian with several years of experience in evaluating digital dermatitis) it is possible to identify cows [which] may require treatment for digital dermatitis. The sensitivity and specificity demonstrated that it may be more practical to use a routine hoof evaluation during milking to establish cows that do not need further evaluation by the hoof trimmer rather than identifying cows that require treatment. The incorporation of regular hoof evaluations during milking may be one step to the reduction of lameness prevalence. PD
—Excerpts from Miner Institute Farm Report, December 2008
Peter Krawczel
William H. Miner Agricultural Institute
krawczel@whminer.com
