Equis ISSN 2398-2977

Anemia: chronic disease

Contributor(s): Prof Derek Knottenbelt, Ruth Morgan, Han van der Kolk, Vetstream Ltd


  • Cause: anemia may be due to decreased red cell production and/or increased red cell destruction.
  • Low grade anemia due to reduced red cell production is common in the horse.
  • Chronic inflammation is an important cause of anemia.
  • In general this anemia is not severe and will resolve when the underlying cause is identified and treated.
  • However, it may become profound and may then be slow to recover even after the initial cause is removed.
  • Signs: most commonly related to the underlying disease process, but may include lethargy and poor performance.
  • Diagnosis: identification of mild to moderate anemia on hematological evaluation.
  • Treatment: treatment of the underlying disease should result in resolution of the anemia.
  • Prognosis: good.



  • Mediators from abnormal cells selectively bind iron.
  • Defects in erythropoietin production may further reduce red cell production.
  • Antibodies generated to RBC altered by drug or neoplastic proteins lead to increased RBC destruction.

Predisposing factors

  • Chronic disease, inflammatory, immunologic or neoplastic.
  • Auto-immune hemolytic anemia   Anemia: auto-immune hemolytic (AIHA)  , secondary to drug reaction or neoplasia.
  • Red Maple toxicity.
  • Folate deficiency, secondary to prolonged trimethroprim sulfonamide   Trimethoprim  medication (over 30 days).


  • There are several mechanisms implicated in the development of anemia associated with chronic disease. Anemia occurs when the rate of production fails to meet the rate of destruction:
    • A block in Fe release from storage.
    • Defective bone marrow response to circulating erythropoietin.
    • Decreased RBC life span.
  • In terms of chronic microbial infection, anemia is protective. Low iron availability reduces bacterial growth rates.
  • Lowered serum iron   Blood: biochemistry - iron  and reduced iron-binding capacity, with increased iron stored in mononuclear phagocytes.
  • There appears to be some defect in the transfer of iron to erythrocyte precusor cells, Interleukin-1 has been implicated.
  • Red cells become small and hypochromic (pale in color).


  • Usually chronic - over weeks or months.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Borges A S, Divers T J et al (2007) Serum iron and plasma fibrinogen concentrations as indicators of systemic inflammatory diseases in horses. J Vet Intern Med 21 (3), 489-494 PubMed.
  • Platt H (1987) Alimentary lymphomas in the horse. J Comp Pathol 97(1), 1-10 PubMed.
  • Tennant B et al (1982) Six cases of squamous cell carcinoma of the stomach of the horse. Equine Vet J 14 (3), 238-243 PubMed.
  • Franken P et al (1982) The bone marrow of the horse. II. Warm-blooded horses with anemia. Zentralbl Veterinarmed (A) 29 (1), 23-27 PubMed.