Bovine leukosis. I. Seasonal influences on lymphocytosis.

The influence of seasons on lymphocytosis status of 321 mature cows from two leukosis herds and a leukosis free control herd was investigated. Animals were bled at three to four month intervals and classifed according to the Göttingen leukosis key as lymphocytosis negative, suspect or positive. The percentage distribution of different hematological classes of animals fluctuated greatly between bleedings, however "persistent lymphocytosis" in animals of leukosis herds was noted to be a constant feature and was not influenced by seasonal variations. The study indicates that 1) multiple samplings are necessary for differentiating between transient and persistent lymphocytosis; 2) caution should be exercised in pooling data from different leukosis herds as these may not be samples from a single leukosis population.