Anemia in Horses

Let’s get one thing out of the way right up front.  Insufficient iron is not the cause of your horse’s anemia, and feeding more iron is not going to fix it. In fact, it might make things worse.  Even if your horse has a source of blood loss, like bleeding ulcers, he has more than enough iron stored in his body to replace that.

Anemia is an abnormally low number of circulating red blood cells

Except for foals raised without access to soil or with heavy parasite burdens, iron deficiency does not exist in horses. Too much iron causes oxidative stress which makes red cells more fragile. It can also cause secondary deficiencies of other minerals critical for red cell production, like copper. If you can’t get iron out of your head, prove it’s not iron deficiency with a serum iron or a full iron panel from KSU’s Comparative Hematology laboratory.

Iron deficiency also causes a characteristic type of anemia called microcytic hypochromic. This means that the red cell size, measured by MCV on the lab report, will be low and hemoglobin concentration,  MCHC, is also low.  If you don’t see this, it isn’t iron deficiency.

Full blown anemia is rare in performance horses but they may develop drops in their red cell counts, which normally run on the high end of normal. The cause here is usually oxidative stress from exercise which makes the red cells more fragile and easily damaged. The solution is to avoid excess pro-oxidants like iron supplements (especially intravenous) and institute supplementation with antioxidant nutrients commonly deficient such as vitamin E, selenium, copper and zinc. Because of the stress they are under and potential compromise of the gut microbiome, B vitamin supplementation may also help.

The most common cause of anemia is horses of all ages is anemia of chronic disease. When the body is under attack from organisms (e.g. Lyme, internal abscess, Strangles), bowel or other organ disease, cancer, severe wounds or burns, iron is made less available because it fuels inflammatory processes and growth of organisms.  This type of anemia will resolve when the underlying condition is corrected.

Older horses with or without PPID (pituitary pars intermedia dysfunction, aka Cushing’s disease) very commonly have a mild anemia with red cells counts and hematocrit/PCV hovering at or just below the lower limits of the laboratory ranges.  The combination of less exercise and an age-related drop in metabolic rate decreases the oxygen requirement of senior horses so some drop in red cell numbers is  physiological. There can also be an element of anemia of chronic disease in many older horses. In any case, the anemia is almost always not the primary problem.

Finally, there are infections that attack the red cells directly, like the Equine Infectious Anemia (EIA) virus, Babesia/Piroplasmosis, Leptospira and Ehrlichia.  These horses are usually obviously ill, have fever and sudden drops in red count.  The horse’s overall condition will alert the veterinarian to look for these disorders.

Sound nutrition is important for creation and maintenance of good red blood cell parameters.  In addition to adequate protein and calories, pay attention to:

  • vitamin E for antioxidant defenses (do not rely on the E in multiingredient mixtures; add it separately)
  • B complex vitamins (especially in older, stressed and compromised horses)
  • generous levels of the usually deficient selenium, zinc and copper, with low to no added iron to compete for absorption

On the herbal front, Echinacea has been documented to support healthy red blood cell production in horses.

Eleanor Kellon, VMD

About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions,, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition .
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