Prevalence of bovine leukemia virus antibody in seven herds of Holstein-Friesian cattle.

Sera from 959 Holstein-Friesian cattle in 7 herds were tested for antibody to bovine leukemia virus, using the agar gel immunodiffusion test with glycoprotein antigen. Seropositive cattle were found in 6 herds; 120 (12.5%) were reactors. In 1 of the herds, the prevalence of seropositive cattle was significantly greater in purebred than in grade cows. Purebred cows raised on the premises and an overall antibody prevalence similar to purchased purebred cows. Purebred cattle more than 2 years old had a significantly greater prevalence of reactors than younger cattle. There was no difference in prevalence by sex.