Abstract

Thrombocytes, well known as important clotting factors, and now known to be important as phagocytic cells, might benefit the study of the avian hemogram. Therefore, blood was sampled from 4 late-stage embryos at embryo day 24, and 4 one-day-old hatchlings (d1), and 5 female ducks aged 59 weeks stained by Wright-Giemsa and examined at 100x. Standard differential counts (SDC) of 2 x 200 cells were used to determine total white blood counts (TWBC) and heterophil/lymphocyte (H/L) ratios. Thrombocytes were not included in the SDC but were studied from photomicrographs. Reactive thrombocytes were present in blood films having a normal TWBC or in the presence of leukocytosis (59 weeks). The H/L ratios may or may not be elevated. Reactive thrombocytes can be differentiated from quiescent types on morphologic criteria. These included an increase in the number of magenta “specific granules”, the development of cytoplasmic vacuoles, and a capacity to form aggregates with other Th or with cells of another series. Reactive Th were not necessarily larger in size than quiescent types. In some instances, Th aggregation with RBC (toroid formation) was with sufficient force to distort the RBC cell membrane. It was observed that reactive thrombocytes were accompanied by bacteria, either free-swimming or attached to cell-associated bacteria. Reactive thrombocytes having lost portions of their cell membrane were regularly encountered. As avian thrombocytes are now recognized as important phagocytic cells, as well as having a primary role in hemostasis, they are part of the immune defense mechanism. The presence of reactive thrombocytes in a hemogram should be considered when using hematological data to evaluate immune responses and establish stress status. © 2022, Journal of World"s Poultry Research. All Rights Reserved.