Development of a linear regression model to estimate within herd prevalence of bovine leukemia virus (BLV) from antibody titer detected by ELISA in bulk tank milk (BTM)

BLV antibody ELISA titers using BTM with the true herd prevalence (Nekouei, 2015). BTM antibody titers can be used as a cost-effective test to estimate the within-herd-prevalence of BLV. The objective is to build and validate new BLV ELISA assay to predict the within-herd-prevalence using the BTM antibody titers with repeated testing over a 3 year period. Material and methods: The true within herd prevalence of BLV was calculated on 34 Maritime dairy farms by individually testing all lactating cows with an ELISA assay using a milk sample for a three year period. BLV antibodies in BTM were tested in triplicate and averaged every 2 months in the first year. The correlation between the true within-herd-prevalence and the mean BLV titre from all 3 rounds of the BTM BLV testing was assessed using simple linear regression and validated using a leave-one-out cross validation test. Results: A total of 4552 individual cows from the 34 farms were tested to determine the with-in herd prevalence . The mean BTM Elisa titre was transformed to square root to meet the assumptions for statistical analysis. BTM testing correlated well with the true within-herd prevalence (R2= 0.61 %). A cross validation test of the final model revealed a very good fit (minimum pseud R2: 0.78 %). Conclusion: Development and validation of this model could be used as an economical tool to determine the with-in herd prevalence for BLV.