Avian erythrocytes are large, nucleated, and elliptical in shape. The presence of nuclei
in erythrocytes complicates hematologic evaluation in these species. Since conventional
automated analyzers perform WBC counts by counting nuclei, these cannot
deal with bird blood. Furthermore, when lysed to allow hemoglobin determination,
the free nuclei cause turbidity in the lysate and must be centrifuged down before
reading spectrophotometrically. Special techniques are required to determine leukocyte counts in birds, such as the use of special staining solutions (e.g. eosinophil Unopettes or Natt-Herrick solution). Most birds display a mild degree of polychromasia in health; this is most prominent in smaller birds (caged or aviary birds) which have a higher metabolic rate.