Chronic iron poisoning from drinking drainage water fatal to horses

In two polders in the Netherlands, horses have accumulated enough iron to suffer chronic poisoning. These animals have been drinking water from drainage ditches with high concentrations of iron for many years, and the accumulation of iron in their organs (hemochromatosis) has eventually led to liver failure. Four horses have since died due to this chronic iron poisoning. Until now, scientists were unaware that horses could suffer iron poisoning.
The sick horses were found in stalls in the Horstermeer polder (Municipality of Wijdemeren) and the Oostelijke Binnenpolder (Municipality of Stichtste Vecht). The water in these drainage ditches contains 9 to 149 times the permitted level of iron contamination in drinking water for livestock.

Have drainage water tested!
“Unfortunately, there is no affordable treatment to cure horses suffering from chronic iron poisoning”, says Mathijs Theelen, specialist in Internal Medicine at the University Equine Clinic, part of Utrecht University’s Faculty of Veterinary Medicine. “In order to prevent more cases of iron poisoning, you would have to test the drainage water before allowing horses to drink it. If the iron concentrations in the water are too high, then the ditch will have to be fenced off. The residents of the affected polders must be informed and take measures to protect their livestock. This problem may affect other polders in the Netherlands, so it is vital that the people living there are informed of the situation.” 

Blood tests necessary
If owners suspect that their horses are at risk or have been at risk in the past, they should contact their veterinarian so that he or she can take blood samples to test for increased levels of iron or indications of liver disease. Then a specialist will be able to provide a diagnosis using liver sonograms and biopsies.

Natural causes
The higher concentrations of iron in the water is probably due to natural causes. In the low-lying polder areas, draining the water draws iron up to the surface from deeper soil layers. Over time, this results in higher concentrations of iron in the surface water. The classic signs of iron contamination, such as brownish orange colouration, are not always present, so it may not be possible to determine whether the water in a drainage ditch has excessive levels of iron with the naked eye.

Mysterious illnesses
If horses drink water with a high concentration of iron every day, then the iron will eventually accumulate in the body, because horses cannot eliminate the iron from their system. If too much iron accumulates in their organs, then the cells will die, which reduces organ function. The liver is the first organ to fail in the horse, which may even cause death. Autopsies of the horses that have died so far indicated iron accumulation in the liver, spleen, lungs, brains and even joints.

Theelen was the person who discovered the diseased horses. “They were seriously ill, but it was a mystery as to what was causing it. After more detailed examinations, and thanks to the involvement of the owners, we realised that they were suffering from iron poisoning, which was a disease that we thought did not occur in horses until now. An exhaustive search for the source of the iron contamination followed, and we eventually narrowed it down to the water in the drainage ditches.”  

More information
Marieke Veldman, Communications Department, Faculty of Veterinary Medicine, Utrecht University, (030) 253 3430, m.m.veldman@uu.nl. 
or: Utrecht University Press Relations, (30) 253 3550, perscommunicatie@uu.nl.