Physiological Factors in the Interpretation of Equine Hematological Profile
Hematology - Science and Practice
574 venipuncture, loss blood, twitching, and pain) and intense exercise (Persson, 1967; 1983) . This response is induced by the release of catecholamines and therefore, the resting PCV in horses should be carefully assessed under different excitation levels (Persson, 1967; Schalm and Carlson, 1982) . By contrast, tranquilizers and anesthetics decreased circulating RBCs, because of splenic sequestration (Jain, 1986) . Comparable changes are not found in splenectomized horses following excitement
... ollowing excitement and strenuous exercise or tranquilization (Kunugiyama et al., 1997) . The intensity of changes in circulating RBC in relation to spleen activity depends on individual variations, age, breed and fitness level and in the case of exercise, duration and intensity. The time required for RBCs to return to resting values is dependent on the degree of the excitement, and it can vary from 40 to 60 minutes to up to several hours (Jain, 1986). Rouleaux formation and erythrocyte sedimentation rate. Rouleaux formation is the result of the aggregation of RBCs in linear stacks and depends on the number of RBCs and their tendency to aggregate. Rouleaux formation is a characteristic finding in healthy horses, as a result of weak surface changes on RBC membranes (Brockus et al., 2003). There is a positive correlation between the rate of rouleaux formation and the rate of setting of RBCs in anticoagulated blood (erythrocyte sedimentation rate). Rouleaux formation is accentuated in some diseases associated with hyperproteinemia, because high concentrations of plasma proteins, particularly fibrinogen and immunoglobulins, have an insulating effect that reduces the RBC surface membrane charge, promoting RBC aggregation (Schalm and Carlson, 1982; Brockus et al., 2003).