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Thrombocytosis is defined as a high platelet count (above 400,000 per microliter). It usually occurs in horses as a secondary result of an existing underlying condition, such as anemia, inflammatory conditions, cancers, or certain infectious diseases. There are however some conditions which cause horses to have a temporary increased platelet count, such as:
  • Recovering from a major surgery
  • Recent traumatic injury which resulted in significant blood loss.
  • Folate or vitamin B12 deficiency
  • Following a strenuous race, event or training session
On rare occasions, an increased platelet count can occur as a primary or essential condition, in which the cause is the direct result of a bone marrow disorder. It is a rare myeloproliferative disorder in which the horse's bone marrow produces an extremely high number of platelets. Horses suffering from thrombocytosis have an increased risk of excessive clotting (thrombosis), due to the presence of the excess platelets.




  • History
  • Clinical signs
  • Platelet test


Diagnostic tests to determine the primary cause, and treatment of the underlying cause with supportive car

Scientific Research References

Good Overviews

Risk Factors