Zinc is involved in over 300 enzyme reactions and is particularly important for hoof quality, skin integrity, coat health, wound healing, and immune function in horses. It is one of the most commonly deficient trace minerals in equine diets, not because hay is especially low in zinc, but because high iron levels in forage and water compete with zinc for absorption. A horse eating hay with 300 parts per million of iron (common in many regions) may absorb significantly less zinc than the numbers on a hay analysis would suggest. This is why many equine nutritionists recommend supplementing zinc even when lab values look adequate on paper.
A 500kg horse needs about 400 milligrams of zinc per day — roughly the weight of a small pinch of salt. Most grass hays provide 150 to 250mg, leaving a shortfall that is worsened by iron interference. Zinc supplementation at 200 to 400mg per day in the form of zinc methionine or zinc sulfate is commonly recommended by equine nutritionists to close this gap.
0.02% of daily nutrient intake
Zinc makes up 0.02% of your horse's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Poor hoof quality (thin walls, slow growth, cracking), dull rough coat, skin lesions or slow-healing wounds, reduced immune response, and poor growth in young horses. Marginal deficiency is widespread and often mistaken for other issues.
Zinc has a wide safety margin in horses. Very high doses (well above 500mg/kg of diet) could theoretically cause copper deficiency by competitive inhibition, but supplemental doses at recommended levels are safe.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 400 | 500 | mg | For a 500kg horse. Many diets fall short, especially when high dietary iron reduces zinc bioavailability. Zinc supplementation (200-400mg) is commonly recommended. |
Source: NRC 2007
Biotin and zinc both play critical roles in hoof and skin health. Biotin provides the building blocks for keratin cross-linking, while zinc supports the enzymes involved in keratin production. Together they improve hoof wall strength and growth rate more effectively than either alone.
What this means: If supplementing biotin for hoof quality, also ensure zinc intake is adequate (400mg daily). Many hoof supplements combine both nutrients. Addressing zinc deficiency alone sometimes improves hoof quality enough to reduce or eliminate the need for high-dose biotin.
Zinc and copper compete for the same absorption pathways. The optimal zinc-to-copper ratio in the equine diet is approximately 3:1 to 4:1. Too much zinc blocks copper absorption, and too much copper blocks zinc. Both minerals are commonly under-absorbed due to high dietary iron.
What this means: When supplementing zinc and copper, maintain a 3:1 to 4:1 ratio. For example, if adding 400mg zinc, include 100-130mg copper. Many equine mineral supplements are already formulated at this ratio. Avoid single-mineral supplements without balancing the partner.
