Circannual rhythms in the blood picture of laboratory rats.

Circannual rhythms of the erythrocyte, total leucocyte, absolute segmented neutrophil and lymphocyte counts in laboratory Wistar rats were found. The highest mean counts occurred in autumn and at the begining of winter. The lowest counts werte recorded in spring and at the begining of summer. A similar circannual rhythm of absolute eosinophil counts in females was also found, but it was not present in males. Circannual rhythms of the relative lymphocyte, segmented neutrophil and eosinophil were not found. The course of seasonal variations in erythrocyte, total leucocyte, absolute segmented neutrophil and lymphocyte counts of males was similar to those of females.