Development of bovine leukosis virus infection in cattle. A preliminary study

A serological study in three herds for 5 to 7 years indicated that BLV infection usually developed when cows where 2 to 4 years old, thereafter, the rate of new infection was somewhat less. The reactor status of the dam had no influence on whether or not and when progeny became reactors. In only one herd 3 calves from 57 reactor cows become persistent reactors, thus there was little evidence of vertical transmission. Such can occur where there is a break in the placental barrier.