Standard machinery used to automatically count white blood cells in dog, cat and human blood works by counting the nucleated cells, but in birds and reptiles it ends up counting both the red and the white blood cells, because they have nucleated red blood cells. Therefore, bird and reptile white blood cells counts are counted manually. So you need to know your cells!

This is a photomicrograph of a blood smear from a blue and gold macaw (Ara ararauna). The most common cells in the picture are mature red blood cells. They are the oval cells with the cigar-shaped, dense nucleus. A slightly younger red blood cell is called a polychromatophil, and it is characterized by being slightly larger than a mature red blood cell, and having a larger, more oval nucleus with less dense chromatin. There is one polychromatophil in this picture in the center left region. If this were a color picture you could also appreciate the slightly blue tinge to the cytoplasm.

There are four cells in the center of this photomicrograph. The cell at the 12 o’clock position is a lymphocyte. It is characterized by being smaller than the monocyte and heterophil, having little cytoplasm and a relatively large nucleus. The cell at the 2 o’clock position is a monocyte. It is characterized by being relatively large with more cytoplasm than the lymphocyte and a nucleus with less dense chromatin. The cell at the 6 o’clock position is a heterophil. It is a granulocyte that is similar to the neutrophil of other species except that is had pink, rod shaped, cytoplasmic granules instead of neutral staining ones. The term "hetero" means different, i.e. it has different staining granules. Last, but not least is the cell in the 9 o’clock position. This is a thrombocyte. Technically, you should not call it a platelet because it has a nucleus. Notice how the thrombocyte looks similar to a lyphocyte, but it is smaller and has little to no clear cytoplasm.

Now you are ready to look at your own avian blood smears. If you want to perform a very rough estimate on the white blood cell count, then you can count the average number of white blood cells on a 40X field and multiply by 2000. Remember, this is a very rough estimate and that it is better to use a quantitative manual counting system.

Cheryl Greenacre, DVM, ABVP, Avian
University of Tennesse, Knoxville