Bovine leukosis. II. Comparison of hematological classification with DNA synthesis between herds.

Blood samples of 126 mature cows with "persistent" hematological status from two leukosis herds and a leukosis free control herd were collected for determining hematological status and estimation of replicating lymphocytes. To quantitate the number of DNA synthesizing cells, the blood was incubated with tritiated thymidine in vitro followed by autoradiography. Classification of animals according to lymphocytosis status did not reveal clearly whether or not a difference existed between the two leukosis herds. The estimation of DNA synthesizing lymphocyte counts showed that the animals from the two leukosis herds did not differ from each other while differing significantly from control herd animals. The study suggests that the similarities between the two leukosis herds, while ambiguous on lymphocyte counts alone, become clear when DNA synthesizing cell counts are compared. Thus the animals of the two leukosis herds belonged to the same "leukosis" population.