Iron plays important roles in the horse's body, including oxygen transport and cellular respiration, which produces the energy expended by horses during exercise. Too little iron leaves horses dull and lethargic, whereas too much can build up in the body.
“Excess dietary iron ultimately accumulates in the liver and certain types of blood cells. Abnormal accumulation of any mineral in the liver negatively influences function and metabolism of that vital organ,” relayed Kathleen Crandell, Ph.D., a Kentucky Equine Research nutritionist. “Iron overload in horses occurs only rarely, and some studies show that short-term excess iron intake does not negatively affect horses.”
In fact, research suggests that horses appear to be able to handle excess dietary intake of iron well, and only horses with an underlying liver condition are likely to accumulate iron in their bodies after ingestion of excessive iron.
“That said, no mammal, including horses and humans, effectively clear excess iron from their bodies. This makes ingesting high levels of iron over time dangerous, especially in young animals,” Crandell explained.
Veterinarians recently reported that 21 genetically unrelated horses managed on eight different farms suffered chronic iron overload. A natural water source was ultimately identified as the culprit. Interestingly, the tested grass and soil on those premises did not contain excess iron levels, which were likely using the same water source to thrive.
Experts recommend having the water tested to ensure it is safe for consumption.
Many owners have concerns that their horses do not receive enough iron in their diet, making iron-laden supplements quite popular. In reality, most horses don't benefit from supplemental iron if fed quality forage or maintained on pasture. For example, typical grass hay contains an average of 198 mg/kg iron while the requirement of the adult horse around 40 mg/kg dry matter, so just the forage portion of the diet alone supplies more than adequate iron.
“If owners ever have any nutrition-related questions, including selection of nutritional supplements, we encourage them to seek the assistance of a qualified nutritionist. Kentucky Equine Research offers dietary consultation, and owners can easily start a conversation with one online today,” advised Crandell.
*Theelen, M.J.P., M. Beukers, G.C.M. Grinwis GCM, et al. Chronic iron overload causing haemochromatosis and hepatopathy in 21 horses and one donkey. Equine Veterinary Journal. In press.
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