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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • Iron deficiency results from chronic external loss of blood (adult horses) or dietary deprivation (usually young foals). Unless adult horses lack access to soil, pasture, or feed, inadequate Fe intake is unlikely
  • Iron deficiency impairs Hb synthesis, impairs RBC maturation, and leads to anemia
  • Anemia and reduced blood Hb concentration may compromise tissue oxygen delivery

Signalment!!navigator!!

  • No breed or sex predilection
  • Rapid growth of foals is associated with high Fe demands. Mare's milk has low Fe concentrations and therefore deficiency may occur in foals with limited access to pasture, Fe-rich soils, forage, or grain

Signs!!navigator!!

  • Clinical signs may be absent or mild due to physiologic compensation
  • Lethargy and exercise intolerance may be the first signs noted
  • When PCV drops below 12%, tissue hypoxia can cause tachycardia, tachypnea, and signs of depression. Pale mucous membranes will be present, and a systolic heart murmur may be noted

Causes and Risk Factors!!navigator!!

Risk factors for chronic hemorrhage include inadequate anthelmintic use, NSAID administration, and toxin exposure.

Chronic, Low-Grade Hemorrhage

  • Severe internal or external parasitism
  • Bleeding gastrointestinal, respiratory, and urogenital lesions (e.g. gastroduodenal ulcers, NSAID toxicosis, neoplasia, hemorrhagic cystitis, guttural pouch mycosis, and ethmoid hematoma)
  • Coagulopathies leading to chronic blood loss (e.g. heritable coagulopathies, warfarin toxicosis, moldy sweet clover)

Diet

Inadequate dietary Fe intake (foals).

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Causes of low-grade, hemolytic anemia include immune-mediated, oxidant-induced, and parasite-induced hemolysis
  • Causes of decreased RBC production include anemia of chronic disease and aplastic anemia

CBC/Biochemistry/Urinalysis!!navigator!!

  • Initial normochromic, normocytic anemia may progress to a microcytic, hypochromic, nonregenerative anemia. Microcytosis often precedes hypochromasia
  • Thrombocytosis may be observed
  • Decreased plasma protein and albumin concentrations are typical with chronic hemorrhage

Other Laboratory Tests!!navigator!!

Initial Stage

  • Decreased stainable Fe in marrow macrophages
  • Decreased serum ferritin concentration (reference range 152 ± 54.6 μg/dL) with serum ferritin < 45 ng/mL highly indicative of Fe deficiency

Later Stages

  • Decreased serum iron concentration (reference range 120–150 μg/dL)
  • Normal or increased TIBC (reference range 200–262 μg/dL)
  • Decreased transferrin saturation (reference range 20–52%) with values < 16% reflecting insufficient iron available for erythropoiesis
  • Decreased mean cell volume with decreased hemoglobin concentration (mean cell hemoglobin concentration)
  • Serum iron, serum ferritin, and TIBC may be affected by conditions other than Fe deficiency including acute and chronic inflammation, renal disease, and corticosteroid therapy

Imaging!!navigator!!

N/A

Other Diagnostic Procedures!!navigator!!

  • Bone marrow cytology may show predominant late rubricytes and metarubricytes, depletion of macrophage iron, and sideroblasts
  • Diagnostic workup of causes of chronic hemorrhage is indicated

Treatment ⬆ ⬇

TREATMENT

  • Horses with lethargy, intolerance to mild exercise, or a PCV < 15% should be restricted to stall rest
  • Blood transfusion is rarely necessary unless PCV drops below 8% or there are clinical and laboratory signs of tissue hypoxia

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Appropriate treatment of causes of chronic blood loss
  • Oral ferrous sulfate (1 g/450 kg body weight) is the safest Fe supplement
  • Iron cacodylate (1 g/adult horse) may be given slowly IV, but must be used with caution owing to the possibility of anaphylaxis

Contraindications/Possible Interactions!!navigator!!

  • Do not use iron dextrans because of idiosyncratic reactions (anaphylaxis and sudden death)
  • Iatrogenic iron overload has been reported in adult horses
  • Do not give foals iron-containing products during the first 2 days of life as fatal hepatopathies may occur

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Monitor serum iron, TIBC, and percentage saturation at ≈2 week intervals
  • Discontinue iron supplementation when values for PCV, serum iron, TIBC, and % saturation return to reference ranges

Prevention/Avoidance!!navigator!!

Nursing foals should have access to pasture and, when appropriate, forage and grain.

Possible Complications!!navigator!!

May result in death if affected animals are left untreated.

Expected Course and Prognosis!!navigator!!

Prolonged iron supplementation may be required.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Age-Related Factors!!navigator!!

Foals are at increased risk owing to high iron demands and limited dietary intake.

Abbreviations!!navigator!!

  • Hb = hemoglobin
  • NSAID = nonsteroidal anti-inflammatory drug
  • PCV = packed cell volume
  • RBC = red blood cell
  • TIBC = total iron-binding capacity

Suggested Reading ⬆ ⬇

Satué K, Muñoz A, Gardón JC. Interpretation of alterations in the horse erythrogram. J Hematol Res 2014;1:1–10.

Author(s) ⬆

Author: Harold C. McKenzie

Consulting Editors: David Hodgson, Harold C. McKenzie, and Jennifer L. Hodgson

Acknowledgment: The author and editors acknowledge the prior contribution of Nicholas Malikedes.