Introduction

• Cause  Anemia: overview  :
  • Primary iron deficiency only likely in very artificial conditions in young foals on milk only diet for over 34 moths.
  • Secondary iron deficiency due to chronic blood loss (usually external bleeding such as gastric ulcers, parasites, failure of clotting, etc).
  • Anemia of chronic disease or inflammation may be thought of as a functional iron deficiency:
    • Commonest cause of mild but persistent (chronic) anemia of horses.
    • Serum iron low but total body iron in storage forms is usually normal but not available.
    • Does not respond to supplemental iron.
• Signs: chronic anemia, reduction in performance.
• Diagnosis: can be differentiated from other causes of anemia by hematological tests/calculations.
• Treatment: iron supplementation.
• Prognosis: guarded due to primary condition.

Pathogenesis

Etiology

• Failure of iron supply (primary).
• Very rare form seen in horses with post-surgical short gut syndrome - iron absorption takes place in mid-jejunum and so loss of large lengths can be responsible for reduction in iron absorption.  History in such cases is usually known.
• Failure of iron availability (secondary) - much more common.

Predisposing factors

• Chronic bleeding site (with external blood loss   Anemia: blood loss  )   →   loss of body iron.
• Surgical removal of long lengths of jejunum.
• Chronic internal infectious/inflammatory processes usually   →    mild to moderate anemia.
• Infections such as internal abscesses (lung   Lung: abscess  , mesenteric or other usually from Bastard Strangles), pleuritis   Lung: pleuropneumonia - bacterial (pleuritis)  , peritonitis   Abdomen: peritonitis  , wounds.
• Neoplastic disease with inflammatory responses (necrosis and secondary infections).
• Paraneoplastic syndrome   Neoplasia: paraneoplastic syndrome  .
• Inadequate diet with no access to pasture.

Pathophysiology

• Iron deficiency due to chronic blood loss   Anemia: blood loss   first causes a decrease in marrow iron, later a decrease in serum iron and the typical microcytic hypochromic anemia is really a late stage finding.
• The small size of the equine red cell makes it difficult to accurately appreciate decreases in cell size and hemoglobin content   Blood: hemoglobin (Hb) concentration  .
• In anemia of chronic disease   Anemia: chronic disease   lack of releasing ability of transferrin makes iron unavailable to red cell production in bone marrow. 
• Microcytic hypochromic anemia is not a common feature of anemia of chronic disease.
• Bone marrow fails to compensate for minor reduction in life span of erythrocytes.
• Impaired erythrocyte production due to failure to access iron and sequestration of older red cells by  reticulo-endothelial system results in a slowly progressive usually modest anemia.

Timecourse

• Slow.
• Progressive.

Diagnosis

Treatment

Outcomes