Thrombocyte morphology and morphometric observations in two vulture species.

Background: The important role of thrombocytes in hemostasis is well documented, but little information is available on the thrombocyte morphology of avian species, including vultures.

Objective: The objective of this study was to describe and compare the morphology and morphometric parameters of thrombocytes in 2 vulture species.

Methods: Blood samples were collected into tubes containing acid-citrate-dextrose from 5 Cape vultures (Gyps coprotheres) and 6 white-backed vultures (Gyps africanus) at the De Wildt Breeding Center, Northwest Province, South Africa. Wright's-stained blood smears were examined by light microscopy. Samples were processed and examined by scanning and transmission electron microscopy (TEM) using standard techniques. Morphometric parameters (perimeter, area, minimum and maximum diameter, and aspect ratio) were measured on 140 thrombocytes using imaging software.

Results: Thrombocytes were predominantly oval to elliptical, with few pseudopodia. The nucleus was the most prominent feature of the cells. Large vacuoles were visible in the cytoplasm by both light and TEM. Ultrastructurally, microtubules and dense bodies were seen in most cells. Other cytoplasmic organelles seen by electron microscopy included mitochondria, endoplasmic reticulum, a surface connecting canalicular system, Golgi complex, lipid droplets, and glycogen. Thrombocytes of Cape vultures had a significantly (P=.005) higher aspect ratio compared with white-backed vultures. Thrombocyte estimates in blood smears were similar in both species, with a combined mean of 31.6 x 10(9)/L.

Conclusion: The morphologic features of thrombocytes in southern African vultures are similar in most ways to those of other avian species. Although thrombocytes in white-backed vultures were slightly more spherical than those of Cape vultures, no other significant differences were found between the 2 species.