Transmission of bovine leukaemia virus in milk.

Nineteen calves born to dams free of bovine leukaemia virus (BLV) did not possess maternally derived precipitating antibody to BLV in their sera after the ingestion of colostrum. Eight of these calves remained serologically negative after being fed milk from BLV-free cows while three (27.3%) of 11 similar calves that had been fed milk from BLV-infected cows developed antibody. Forty-four of 47 calves born to BLV-infected dams acquired maternal antibody to BLV after ingesting colostrum. Two (8.7%) of the 23 calves fed milk from BLV-free cows developed antibody to BLV probably as a result of transplacental or colostrum infection whereas four (16.7%) of the 24 calves fed milk from BLV-infected cows developed antibody. It is concluded that milk transmission of BLV is responsible in part for the high rates of infection encountered in our dairy herds and that calves lacking specific maternal antibody are more susceptible to BLV infection through the ingestion of milk than are calves with maternal antibody.