Introduction

• The life-span of equine erythrocytes is about 100 days.
• Anemia is defined as a deficiency of erythrocytes either in number or volume or both.
• Cause:
  • Hemorrhage: internal vs external, acute vs chronic.
  • Hemolysis: intravascular vs extravascular, immune-mediated (primary or secondary), direct toxic damage, oxidative damage, infectious disease.
  • Increased use/shortened half-life of RBCs.
  • Decreased production.
• Signs: depends on the degree of chronicity of the anemia. Common features include pallor or jaundice, lethargy, weakness, collapse, poor performance/exercise intolerance.
• Diagnosis: hematological evaluation, including a blood smear, is essential for the identification of anemia.
• Treatment: depends on the cause of the anemia.
• Prognosis: depends on the cause of the anemia.

Pathogenesis

Etiology

• Hemorrhage: external or internal blood loss.
• Hemolysis: destruction of red blood cells:
  • Immune-mediated (primary or secondary).
  • Toxic: direct, eg following DMSO administration, or oxidative damage, eg red maple leaf or onion ingestion.
  • Infectious disease, eg equine infectious anemia, babesiosis, ehrlichia.
• Anemia of chronic disease: increased use and shortened red blood cell lifespan.
• Failure of production: myelophthisic disease, eg bone marrow neoplasia, renal disease resulting in reduced production of erythropoietin.

Predisposing factors

• Hemorrhage.
• Blood loss due to:
  • Internal or external parasitism.
  • Gastrointestinal ulceration   Stomach: gastric ulceration  .
  • Gastric squamous cell carcinoma.
  • NSAID-toxicosis   Toxicity: non-steroidal anti-inflammatory (NSAID)  .
  • Ethmoidal hematoma   Ethmoid: hematoma  - can produces mild anemia.
  • Guttural pouch mycosis   Guttural pouch: mycosis  ; peracute arterial bleeding.
  • Disseminated intravascular coagulopathy (DIC)   Disseminated intravascular coagulation  /hemorrhagic diathesis.
  • Exercise-induced pulmonary hemorrhage   Lung: EIPH (exercise-induced pulmonary hemorrhage)  .
  • Trauma.
  • Surgical procedures, eg castration   Testis: castration - overview  .
• Hemolysis:
  • Exposure to drugs, eg DMSO   Dimethyl sulfoxide  , penicillin   Penicillin G  , TMPS, phenothiazine, phenylbutazone   Phenylbutazone  .
  • Exposure to toxins, eg red maple leaf, onions, arsenic.
  • Infection, eg EIA   Equine infectious anemia (EIA)  , babesiosis   Babesiosis  , ehrlichiosis   Potomac Horse Fever  .
• Chronic disease.
• Renal disease   Kidney: disease - overview  .
• Neoplasia.

Pathophysiology

• Anemia can be induced via several mechanisms.
• Hemorrhage: external or internal blood loss.
• Hemolysis: destruction of red blood cells:
  • Immune-mediated (primary or secondary).
  • Toxic: direct, eg following DMSO adminitration, or oxidative, eg red maple leaf or onion ingestion.
  • Infectious disease, eg equine infectious anemia   Equine infectious anemia (EIA)  , babesiosis   Babesiosis  , ehrlichiosis   Potomac Horse Fever 
• Anemia of chronic disease: increased use and shortened red blood cell lifespan.
• Failure of production: myelophthisic disease, eg bone marrow neoplasia, renal disease resulting in reduced production of erythropoietin.
• Some diseases induce anemia by more than one mechanism, eg EIA, causes both hemolysis and reduced red cell production.
• Lymphosarcoma might induce anemia both via myelophthisis and via immune-mediated mechanisms.

Timecourse

• Anemia in case of equine infectious anemia   Equine infectious anemia (EIA)  is progressive and cyclic.
• Anemia following (severe) blood loss   Anemia: blood loss  /trauma is seen suddenly - not always external bleeding.
• Rapid onset anemia:
  • Blood loss   Anemia: blood loss  .
  • Hemolysis.
• Slow onset anemia:
  • Bone marrow suppression.
  • Parasitism.

Diagnosis

Treatment

Prevention

Outcomes