Objective—To determine the association between
serologic status for bovine leukemia virus (BLV) and
culling rates by use of survival times in a commercial
Holstein dairy herd.
Animals—593 milking cows.
Procedure—Cattle were tested for antibodies against
BLV by use of agar gel immunodiffusion or ELISA 4
times each year from 1989 to 1993 and then annually
through 1999. Dates of birth, first calving, and culling
or death were obtained from Dairy Herd Improvement
Association records. Most cows were enrolled in the
study on the date of first calving. Survival times were
compared among seropositive, seronegative, and
seroconverted cows with the Kaplan-Meier method
and a Cox regression model stratified on the basis of
year of birth.
Results—Complete records were available for 593 of
685 (87%) cattle in the dairy herd during the study
period. Median survival time for all cows was 31.7
months. Survival times, which correspond to cull
rates, did not differ significantly between seropositive
and seronegative cattle, whereas cattle that seroconverted
during the study had a significantly longer survival
time. Year of birth was positively and significantly
associated with survival time.
Conclusions and Clinical Relevance—BLV serologic
status was not associated with cull rate as measured
by survival time in this dairy herd. This finding is in
contrast to results of studies that used survival analysis
techniques; our results may influence management
decisions concerning BLV. (J Am Vet Med Assoc