BLV-antibodies in serial sampling over five years in a bovine leukosis herd.

The sequential monthly bleedings of bovine leukosis herd animals showed that a majority of the animals was positive for BLV-antibodies at the age of 1 1/2 years or over and remained reactors throughout the observation period. Two phases of BLV-antibodies were observed in the calves born in the herd. In the first phase the calves remained reactors for two to seven months, indicating residual maternal antibodies acquired through colostrum. In the second phase, the animals became permanent reactors reflecting an active concomitant infection with BLV. The degree of spread of BLV infection among the leukosis herd animals appeared to depend upon the ratio between reactors and negative animals.