Bovine leukemia virus: Duration of BLV colostral antibodies in calves from commercial dairy herds

A study was conducted to determine the duration of colostral antibodies to bovine leukemia virus (BLV) in diary calves from commercial dairy farms. Sera of pregnant dams from four different dairy farms and sera of the calves of these dams were analyzed for BLV antibodies using the agar gel immunodiffusion (AGID) test. Precolostral serum samples were collected from the female calves of known BLV serologically positive dams. Postcolostral serum samples of the same calves were collected on Day 2 and biweekly until 2 consecutively negative AGID tests performed 4 weeks apart were obtained. Subsequently, the biweekly serum samples from each calf were analyzed quantitatively for BLV antibodies with the AGID test. End-point titers were determined using phosphate buffered saline to make two-fold dilutions. A logarithmic transformation of the inverse of the end-point titer was used to determine the regression line of antibody decay for each calf. Estimated weighted regression analysis was used to determine the least-squares regression line for 27 of the 38 calves sampled. The duration of colostral antibodies was calculated as 71 days using the prediction equation. The minium and maximum durations of colostral antibodies were 14 days and 147 days, respectively. The half-life of the antibodies was 36.05 days. Factors affecting the duration of BLV colostral antibodies and the practical applicability of this study were discussed.