Iron deficiency is a relatively uncommon disorder of dogs, characterized by iron levels below the normal range of 46 – 241 μg/dL..
Traditionally it was associate with insufficient meat intake or lack of access to iron-containing soils, but modern diets have virtualy eradicated this disease in domestic dogs in developed countries.
Iron in the form of heme is vital to many metabolic functions including oxygen transportation in hemoglobin. Iron is also a component of multiple enzymes, including cytochromes, necessary for energy generation and drug metabolism.
Through the donation or acceptance of an electron, iron exists in either a reduced ferrous (Fe2+) or an oxidative ferric (Fe3+) state. The majority of functional iron is contained in hemoglobin, with smaller quantities found in myoglobin and cytochromes. The liver, which is the site of production of iron transport proteins, contains the largest non-functional iron stores either as ferritin or hemosiderin. Ferritin is both diffuse and soluble, and is the primary iron storage protein. Hemosiderin is similar in structure, but has more iron relative to protein and is insoluble. Iron is also stored in reticuloendothelial cells of the bone marrow and spleen.
Ferrous iron is absorbed mainly in the duodenum, then bound to transferrin in the plasma and transported for use in target organs or storage.
Iron deficiency results when either dietary intake does not meet the dog’s requirement or when there is chronic external blood loss. The dietary iron requirement for adult dogs s 80 mg/kg and is higher in puppies due to their rapid growth.
Inadequate intake is rare except in nursing pups due to the low concentration of iron in milk. Inadequate dietary iron intake does not occur in dogs fed commercial pet foods, but can rarely occur with home-cooked and vegetarian diets without appropriate iron supplementation.
High iron content is found in meat products (such as liver, heart, and muscle), but also in brewer’s yeast, wheat germ, egg yolks, oysters, some dried beans, and some fruits. Green vegetables, cereals, fish, and fowl have an intermediate amount of iron.
Foods low in iron include milk, milk products, and most non-green vegetables.
Clinical signs in affected dogs are often vague but include lethargy, decreased exercise tolerance, weight loss, retarded growth, pica and generalized malaise. In more severe cases, bounding pulses, arrhythmia and a systolic heart murmur may be evident.
Initially, reticulocytosis is present due to increased production and release of reticulocytes secondary to anemia. However, as iron stores are depleted and the iron deficiency becomes more severe, the absolute reticulocyte count becomes inadequate for the degree of anemia.
A differential diagnosis would include other causes of anemia such as enteric- or hemo-parasites.
In mild cases, oral iron therapy is usually preferred over parenteral iron administration due to its low cost and higher safety.
Iron injections are usually curative, with iron dextran can be given at 10 mg elemental iron/kg weekly, but in dogs with PCV <15, blood transfusions may be required.
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