Enzootic bovine leukosis: prevalence of blood lymphocyte nuclear pockets in dairy bulls in the United States and foreign countries.

Studies of the incidence of enzootic bovine leukosis-related blood lymphlymphocyte nuclear pockets (LNP) were made of 743 dairy breed bulls in the United States and foreign countries. Statistical evaluation disclosed that the prevalence of these anomalous nuclear forms in the studs observed is significantly greater in the United States than in other countries. In particular, the average percentage of LNP-containing cells in each United States stud is estimated to be more than twice the level found in all but two non-United States studs studied and more than three times the level in the majority (10 of 19) of them. Moreover, United States studs exhibited a higher proportion of LNP-suspicious and -positive cases than almost all of the non-United States studs. We believe this is valid evidence that serves to reinforce the expressed need for a federal surveillance program for enzootic bovine leukosis in the United States.