If you’ve been told your horse is anemic and probably needs iron, think again. We think of iron when we hear anemia because it’s commonly involved in people, but that’s not the case in horses. Iron is essential in your horse’s diet, but diet-related deficiencies are unlikely. In addition, excess iron is toxic.
Before you start pumping your horse full of iron, ask your vet to check the horse’s iron status. And get the tests you need. Serum iron level alone won’t tell you anything. You also need total iron binding capacity — a measurement of how saturated the horse’s iron binding protein (transferrin) is, and a serum ferritin. Ferritin is the protein that binds iron in storage form, keeping it from circulating free and causing damage to body tissues.
Interpreting The Results
Serum Iron: Upper normal for most labs is 150 ug/dL. The higher the iron, the more iron your horse has in his diet. Very high iron intakes will increase any horse’s serum iron. A rupture of the red blood cells will cause a false elevation of this test. Fasting may cause a false low reading.
Total Iron Binding Capacity (TIBC): Most horses run in the 250 to 350 ug/dL range. TIBC is an indirect measurement of the level of the protein transferrin, which shuttles iron around in the body. TIBC levels generally parallel serum iron. TIBC itself doesn’t tell you too much, but Transferrin Saturation Index (TSI) does. Most horses will run in the 30 to 35% range for TSI. When iron overload is developing, TSI rises.
Ferritin: Ferritin is the storage protein for iron. Most horses are in the 100 to 200 ng/ml range, but anemia isn’t a concern until ferritins dip down to about 20. The higher the ferritin, the more iron is stored in the body tissues. Primary storage sites are liver and spleen. Some horses are so heavily loaded with iron that their livers are found to be black on postmortem examinations.
Both false high and false low readings for ferritin do occur. By ”false” we mean the value doesn’t truly reflect the horse’s iron stores. Pregnancy causes a false low test result for ferritin. During pregnancy, the mare’s body lowers ferritin production to make sure adequate iron is available to the growing foal.
Infections, inflammation and malignancy can cause false high ferritin readings. It is one of the body’s protective mechanisms. Many organisms and cancer cells are highly dependent on iron for their growth and multiplication.
By increasing ferritin, the body is trying to keep iron away from them. Iron is also very pro-inflammatory, so the body will sequester more iron to protect itself from runaway inflammation.