Protection of colostral antibodies against bovine leukemia virus infection in calves on a California dairy.

A three-year prospective study involving 244 calves was undertaken on a California dairy to evaluate the protective role of colostral antibodies against bovine leukemia virus (BLV) infection in calves. Calves were followed from birth to the time they left their individual hutch (TLIH), at about 90 days of age. The probability of being infected at TLIH and the daily risk of infection between birth and TLIH were modelled using the logistic and the Cox models, respectively. Calves with no detectable antibodies during the first week of life were up to 2.00 and 2.75 times more likely to be infected at TLIH compared to calves with low and high concentrations of antibodies during the first week of life, respectively (p = 0.01). When the daily risk was modelled, calves without antibodies at the estimated day of infection were up to 3.4 and 11.6 times more likely to become infected than calves with low and high concentrations of antibodies on that day, respectively (p less than 0.001). Results indicated that calfhood infection may be reduced by about 45% through the feeding of colostrum with BLV antibodies. Further reduction in infection may be possible by feeding calves milk powder, milk replacer, and/or milk from noninfected cows. Results also indicated that quantification of the effect of a time-dependent risk factor, such as colostral antibody concentration, might be affected if treated as a fixed factor.