Effect of colostrum replacer containing bovine leukemia virus antibodies on infection and antibody level in young calves

In this study, we aimed to investigate whether a commercially available spray-dried colostrum replacer containing bovine leukemia virus (BLV) antibodies could increase serum antibody levels and prevent early BLV infection in newborn calves. The sample-to-positive ratio (S/P value) of anti-BLV antibodies in 10 batches of the colostrum replacer was 2.48 ± 0.33 (positive value ≥0.3), as determined by ELISA. Fourteen calves born to BLV-negative mothers and fed maternal colostrum were assigned to the control group. Another 14 calves, separated from their dams immediately after birth and fed 450 g of colostrum replacer within 6 h, formed the test group. Calves were allocated into groups alternately by birth order. Serum S/P ratio of BLV antibodies was monitored d 1 to 84. The control group maintained near-zero antibody levels throughout the study period. Conversely, the test group had an antibody value of 2.36 ± 0.54 on d 1, which declined over time but remained positive in all calves until d 56. These results suggest that colostrum replacers containing BLV antibodies can confer passive immunity and reduce early-life BLV infection risk.