Hematology

The predominant peripheral blood leukocyte in rats is the lymphocyte, which makes up approximately 80% of the cell population. Nuclear ring forms are common among granulocytes in tissues, as in the mouse. Eosino­phils tend to possess annular, ring-shaped nuclei with­out lobation. Basophils are rare. Mature male rats have higher total leukocyte counts than do females, in both lymphocytes and granulocytes. Splenic hematopoiesis occurs in the adult rat, but not to the extent seen in mice. Prominent hematopoietic activity usually denotes an underlying disease state. In pathogen-free rats, splenic hematopoiesis is minimal, with only a few megakaryo­cytes present.