Haematological Alterations Observed in Equine Routine Complete Blood Counts. A Retrospective Investigation *

Abstract

Results on more than 1000 complete blood counts (CBC) performed on hot-blooded horses, in- cluding Thoroughbred, Standardbred, and Arabian, have been reviewed. All the data were processed and stored at the Laboratory of Haematology, Department Veterinary Clinic, University of Pisa, over the last 2 years, and involved samples withdrawn from both inpatients and outpatients of the clinic. The CBC is routinely requested as a part of a complete clinical evaluation of horses as well as during the course of disease or as a routine check during the training process. The CBC, using K3-EDTA blood sam- ples, included a three cell population count performed on an electronic impedance cell counter (Genius, SEAC, Calenzano, Fi, Italy), and the microscopic evaluation of a stained blood smear. In addition, the refractometric assessment of total plasma proteins and ¢brinogen (by the heat precipitation method) was also performed using EDTA plasma. The incidence of haematological changes in red blood cells (RBCs), subtyped as polycythaemia and anae- mia, were 16.2%. Anaemia totalled 15.1%, including mild (packed cell volume (PCV) 31^26%) at 10.2%, moderate (PCV 25^17%) at 4.1%, and severe (PCV 516%) at 0.8%. The incidence of white blood cell (WBC) changes, subtyped as leucocytosis and leucopenia, was 38.4%. Leucocytosis totalled 30.5%, including mild (WBC 10^15 000/ml) at 22.5%, moderate (WBC 15^20 000/ml) at 7.7%, and severe (WBC 420 000/ml) at 0.3%. The incidence of leucopenia was 7.9% (WBC 55500/ml). Inter- pretation of the full leucogram (including variation on several leucocyte types and ¢brinogen values) gave an incidence of physiological leucocytosis at 9.9%, stress leucocytosis at 5.3%, and in£ammatory leucocy- tosis at 37.3%. Thrombocytopenia was frequently observed at 7.2%, whereas thrombocytosis was observed in only 0.3% of cases. Horse CBCs display less characteristic blood pictures in comparison to other species due to their parti- cular haemopoietic system, such as the long half-life of RBCs, the occurrence of a non-sinusoid spleen, the fate and distribution of WBCs, and the rather high clumping phenomena of horse platelets in EDTA glass vials.