Heavy Metals in the Horse’s Diet

It’s commonly known that horses need trace minerals that may be absent in the diet. Common ones are copper, zinc, and sometimes manganese. Rarely, are the toxic heavy metals discussed. This newsletter discusses some of the more common ones, possible symptoms that low-level exposure may cause, and how to make better decisions for your horse.

Why be concerned about heavy metals?

Heavy metal exposure can cause a variety of symptoms. This can be from the direct toxicity of the heavy metal. Or it can be from inhibiting the absorption of other minerals necessary for good horse health.

Exposure to heavy metals can come from:

Our horse’s feed. This can be hay, bagged feed, or supplements that we purchase. This is an important area because we have control over their feed intake.

Environment. This is a significant area of exposure to heavy metal exposure. Since we have minimal control over these factors, this will not be the focus of this newsletter.

What are some of the symptoms of heavy metal exposure?

Heavy metal exposure frequently causes a low-level inflammation within the body and an increase in oxidative stress. The symptoms that are displayed depends on the heavy metal. Common ones include:

» Developmental abnormalities.

» Gastrointestinal upset, such as chronic diarrhea, fecal water syndrome, ulcers, abdominal pain, weight loss.

» Neurological deficits, such as ataxia, peripheral neuropathy, weakness, or uncoordination.

» Depression.

» Coat and skin changes, such as a rough or unhealthy appearance.

How you can best help avoid heavy metal poisoning in your horse.

One of the biggest ways to help your horse is to understand what your horse is eating and drinking.

Has your horse experienced a change since changing feed or hays?

Where is your hay from?  Is there a regional mineral profile for the area?

➡ Was the hay from an area that is known to be a mining area, with a potential for increased heavy metals?

➡ Did you recently change barns? Does the barn have water provided through old lead pipes?


What is in the supplement that you feed?

This one an area that horse owners rarely think about. We think that because it’s on the tack store shelf, then it must be safe. There are numerous supplement examples that need to be questioned. These are just a few:

Kelp can have a high variability of iodine, from very little to extremely high levels. Does the label or manufacturer say how much iodine is in the supplement? A better choice may be to add iodized salt to the horse’s diet instead.

Calcium carbonate can have high levels of lead. Calcium supplementation is common for pregnant mares and growing foals. However, when high levels of lead are present, it can be the source of neurological problems, especially in young horses. Lead can also cross the placental barrier and cause problems to the unboarn foal. 

Magnesium oxide is another supplement that can have high levels of iron, lead, cadmium and arsenic. Because there are so many different grades of magnesium oxide, quality is extremely important. Did the company source the least expensive magnesium oxide? Or is it human food grade, with higher standards?

Rice bran has higher arsenic levels than polished rice. Other type of bran, such as wheat, oat, or barley, have significantly less arsenic.

Difficulty in determining if low level heavy metals exposure.

Heavy metal toxicity isn’t apparent until it’s well advanced. The horse’s body systems attempt to cope with the increased level of heavy metals by sequestering it in the tissues. Vague symptoms may occur until the heavy metal level is so high that overt symptoms occur. These vague symptoms can mimic many other ailments, such as EPM, Lyme disease, filaria, or ageing.


Take home message:

Best practice is to minimize chronic low-level heavy metal exposure at all stages of life.

Be aware of what you’re feeding your horse. The biggest impact that you, as a horse owner, can do is to minimize the exposure to heavy metals. Always opt for quality feed and supplements. Choose supplements that have lower levels of the heavy metals. In our quest to help our horse, we want to be sure that we are making the best choices possible.


Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.


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