From Chronic Iron Overload to Equine Hemosiderosis

In the Dutch polders, horses often drink from ditches that border the pastures. Two horses from this area were presented at Utrecht University with haemosiderosis and liver disease. Because they were not genetically related but came from the same stable, the vets became suspicious. They examined other animals, and indeed: All nine horses from the stable were affected, as were five of the seven other horses examined from neighboring farms. After an appeal in the media, six more animals were diagnosed: A total of 21 horses and one donkey from eight different stables suffered from liver disease and haemosiderosis.

The study included Equidae showing signs of chronic liver disease, such as jaundice, weight loss, thinning, lackluster fur, or elevated liver enzymes, and whose blood transferrin saturation was over 80 percent. A liver biopsy was taken from seven horses, seven others were pathophysiologically examined: there were histological signs of hemosiderosis.

Environmental samples revealed the ditch water as a problem. It has been the main drinking water source for most diseased horses for years. The iron concentration was between 0.74 and 72.5 mg Fe/l, from 0.3 mg Fe/l water is unsuitable for animals. Grass and soil were also checked, but here the iron content was not as high.

Nine out of 22 animals had to be euthanized. The others were doing reasonably well at the end of the study, years after diagnosis, but still had signs of chronic disease.

Mammals cannot actively excrete iron, so there is theoretically always a risk of toxicosis when ingesting larger amounts. In horses, however, only a few cases of acute iron poisoning after the consumption of iron-containing feed supplements have been found in the literature. In 2001, Pearson and Andreasen fed horses iron excess for eight weeks with no lesions found in subsequent liver biopsies. This study at the time concluded that iron poisoning in horses was unlikely. This is now refuted by the current study from Utrecht. However, the Dutch horses picked up the shoes over a much longer period, all having been kept in the same conditions for at least the last nine years.

Iron storage disease should therefore be ruled out in horses with chronic liver disease and access to natural water sources. Evidence of a possible excess of iron is an increased iron serum content and increased transferrin values, a reliable diagnosis is only possible with the help of a liver biopsy.

Therapy is symptomatic, the use of chelating agents is theoretically possible, but very expensive, and bloodletting is controversial. The most important measure is to identify the source of iron and to ensure that the metal does not continue to be consumed in excess. Incidentally, it is not always possible to tell whether the water contains too much iron: only Fe3+ ions are responsible for the typical orange-brown discoloration. Fe2+ ​​ions are colorless.