Until recently, the veterinary industry has viewed iron toxicity in equids mainly as an acute condition—the result of overdosing on iron-containing supplements. However, researchers have found that equids exposed to high iron levels in water, grass, or hay over a prolonged period can accumulate the mineral in their livers, resulting in chronic iron overload.
Dutch researchers took a closer look at chronic iron overload after two genetically unrelated horses from one farm in the Netherlands were diagnosed with hemochromatosis (a buildup of excess iron in the body) and liver dysfunction. In all, the team examined 22 cases (21 unrelated horses and a donkey from eight farms) with evidence of hemochromatosis in blood or liver tissue samples. The equids displayed clinical signs of jaundice, weight loss, rough hair coat, and dullness.
The researchers tested water samples from the farms, all of which had high iron levels ranging from 0.74 to 72.5 mg Fe/L—above the maximum acceptable limit of 0.3 mg Fe/L—and were deemed unsuitable as drinking water for animals, they said.
Veterinarians treated affected equids based on their clinical signs and with supportive therapy, including electrolyte infusions, corticosteroids, antibiotics, NSAIDs, opioids, vitamin E supplementation, and/or omeprazole. They euthanized five affected animals ultimately diagnosed with liver failure. Four other horses’ clinical signs continued to worsen, and they were euthanized nine months to 4.4 years after diagnosis.
Post-mortem examination revealed the affected equids’ livers were smaller than normal, rusty-brown in color, and often had a nodular appearance. The researchers also discovered iron accumulation in other organs, including the pancreas, lungs, spleen, brain, kidneys, intestines, thyroid, and adrenal glands.
The team said 13 of the 22 equids had survived as of Jan. 1, 2018, but their conditions hadn’t changed significantly.
“We did follow-up bloodwork on several horses—up to five years later—and iron levels were still very much elevated,” said Mathijs J.P. Theelen, DVM, Dipl. ECEIM, EBVS, an assistant professor at the Utrecht University Faculty of Veterinary Medicine, in the Netherlands. “They did not differ from values at time of diagnosis, despite keeping iron intake to a minimum.”
So how can you keep your horses safe from chronic iron overload?
Theelen recommended testing your feed and water’s iron levels, especially in areas with high levels of iron in the soil. He also said to avoid long-time administration of supplements high in iron. Unless your veterinarian prescribes such a supplement for a specific medical condition, “this is generally not necessary in horses,” he said.
The study, “Chronic iron overload causing haemochrmatosis and hepatopathy in 21 horses and one donkey,” was published in the Equine Veterinary Journal.