• horse;
  • platelet activation;
  • anti-fibrinogen antibody;
  • platelet-neutrophil aggregates


There is evidence that equine platelet reactivity is altered by strenuous exercise. Changes in platelet reactivity could impact haemostasis following exercise-induced injury and may play a role in the pathophysiology of exercise-induced pulmonary haemorrhage. Interpretation of results of previous studies is hindered by potential in vitro-induced changes in platelet activity through the choice of anticoagulant and the use of platelet inhibitors. The present study was undertaken to re-evaluate the effect of exercise on equine platelets using methodologies that minimise in vitro-induced changes in platelet activation.

The percentage of platelet-neutrophil aggregates increased significantly (P = 0.01) from mean ± s.e. 3.5 ± 0.6% at rest to 7.2 ± 1.3% during exercise. There were no significant changes in binding of anti-fibrinogen antibody or annexin V to platelets in response to exercise.

An inability to detect increased binding of fibrinogen or annexin V may be a result of poor test sensitivity or low statistical power. Alternatively, activated platelets may be quickly removed from the circulation and miss detection. The significance of increased numbers of platelet-neutrophil aggregates in association with exercise is currently unknown and warrants further investigation.