USE OF SURVIVAL ANALYSIS TO COMPARE CULL RATES BETWEEN BOVINE LEUKEMIA-VIRUS SEROPOSITIVE AND SERONEGATIVE DAIRY-COWS

Bovine leukemia virus (BLV) infection and culling of cows in a commerc ial dairy herd were evaluated to determine whether a relation existed between the 2 factors. Cattle from the study population, a Holstein da iry herd consisting of approximately 400 milking cows, were tested for antibodies to BLV, using the agar gel immunodiffusion test, semiannua lly for 2 years, annually for 2 years, and when cattle were culled. Co mplete records of BLV test results were available for 849 (79%) of the 1,078 cattle that had at least 1 test during the study period. Using the Cox hazard model, the cull hazard rates (culls/cow-months) were gr eater for BLV seropositive cows than for seronegative cows > 36 months old. Hence, among older dairy cows, BLV-infected cows were culled pre maturely, compared with uninfected cows.