DETECTION OF BOVINE SOMATOTROPIN TREATMENT IN DAIRY-CATTLE PERFORMANCE RECORDS

Effectiveness of cluster analysis in detecting application of bST was examined. Field data were manipulated by adding a specified percentage of the true performance to original test day records to simulate application of bST. The partly manipulated data then were analyzed using cluster analysis. Test day milk production data came from 42,779 cows of the Bretagne (Northwestern France) that had test days between 1986 and 1989. As criteria in the cluster analysis for differentiation between treated and untreated cows, parameters of the incomplete gamma function along with other variables calculated from test day records were used. The best differentiation was achieved when a persistency parameter, defined as the ratio of second divided by first trimester production, was used as a variable in the cluster analysis. For the assumed scenario of bST application, more than 80% of all cows were classified correctly under random use of bST. Systematic treatment led to improved results.