Minerals, water and soil

Minerals are often over-supplemented or overlooked — and it is not only the feed that matters, but the water and soil too. A few insights.

Most horses get too much iron, not too little

Horses on forage in Europe are rarely short of iron — grass and hay usually supply several times the requirement. The more common problem is excess iron, which competes with copper and zinc and can create shortfalls of those minerals. Routine iron supplements are almost never justified.

Dutch and Belgian soils are among the most selenium-poor in Europe

Horses kept only on locally grown forage in the Netherlands and Belgium are very likely to be short of selenium unless it is supplemented. Here, selenium supplementation is the norm rather than the exception — but it should still be confirmed by testing, because selenium has a narrow safety margin.

Stacking supplements is the usual route to selenium overdose

Selenium has the narrowest safety window of any trace mineral in the horse. The commonest way horses are over-supplemented is by feeding several products at once — each safe on its own, but together tipping over the limit. Always add up selenium across everything in the bucket.

High-sulphur groundwater can quietly lock up copper

In parts of the Netherlands and Belgium, groundwater is high in sulphate. In the gut this forms compounds that bind copper tightly and permanently, so a horse on apparently adequate copper can still be functionally deficient. Water chemistry matters as much as the feed label.

Iron in well water can cause copper deficiency

Many properties on private wells have iron-rich water. Iron and copper compete for the same absorption route, so high water iron can produce copper-deficiency signs even when copper on paper looks fine. It is worth measuring water iron before making copper decisions.

Kelp and seaweed are a real iodine-overdose risk

Seaweed-based supplements can contain enormous amounts of iodine — sometimes 600–1000 mg per 100 g. In pregnant mares the threshold for harming the foal's thyroid is just 25 mg of total dietary iodine a day, and the consequences for the foal are severe and permanent. 'Natural' does not mean 'safe in any amount.'

Spring grass can block magnesium absorption

Fast-growing spring grass is often very high in potassium, which competes with magnesium for uptake. Lactating mares are most at risk, because their magnesium need peaks at exactly the time this effect is strongest.

Magnesium does not fix insulin resistance in horses

Magnesium is often recommended for metabolic horses based on human research. In horses, there is no peer-reviewed evidence that it improves insulin sensitivity — the human finding simply does not carry across.

This is general information. It does not replace the individual feeding plan your EVN vet prepares for your horse after assessing it.