Zinc for Horses: The Silent Deficiency in UK Diets
If you had to guess the single most commonly deficient mineral in UK horse diets, what would you say? Iron? Calcium? Most horse owners would never guess zinc — but that's exactly what it is.
Zinc is a trace mineral that plays a role in hundreds of biological processes, from hoof growth to immune function. Yet the vast majority of horses grazing UK pastures or eating UK-grown hay are not getting enough of it. Not even close.
In this article, we'll look at why zinc matters so much, why UK diets consistently fall short, and what you can do to make sure your horse isn't one of the many suffering from a quiet, chronic deficiency.
Why Is Zinc So Important for Horses?
Zinc is involved in over 300 enzymatic reactions in the horse's body. That's not a typo — it really is that fundamental. Here are some of the key areas where zinc plays a critical role:
Hoof Health and Integrity
Zinc is essential for keratin production, the structural protein that makes up the hoof wall, hair, and skin. Horses with chronically low zinc intake often develop poor-quality hooves that are soft, crumbly, prone to cracking, and slow to grow. If your farrier is constantly commenting on the quality of your horse's feet, zinc status is one of the first things worth investigating.
Skin and Coat Condition
A dull coat, slow shedding, flaky skin, and increased susceptibility to conditions like mud fever and rain scald can all be linked to inadequate zinc. Zinc supports the skin's barrier function and plays a role in wound healing. Horses that are slow to heal from cuts, scrapes, or skin infections may well be zinc deficient.
Immune Function
Zinc is a cornerstone of a properly functioning immune system. It supports the production and activity of white blood cells and helps regulate the inflammatory response. Horses on low-zinc diets may be more susceptible to infections and slower to recover from illness.
Growth and Development
For young, growing horses, zinc is particularly important. It's involved in cell division, protein synthesis, and bone development. Deficiency during growth can lead to developmental problems, poor growth rates, and suboptimal bone mineralisation.
Reproductive Health
In breeding stock — both mares and stallions — zinc plays a role in fertility, foetal development, and milk production. It's a mineral that simply cannot be overlooked in any stage of life.
Insulin Sensitivity and Metabolic Health
Zinc is involved in insulin signalling and glucose metabolism. There is growing interest in the role of adequate zinc status in supporting metabolic health, particularly relevant for the many UK horses and ponies prone to equine metabolic syndrome (EMS) and laminitis.
How Much Zinc Does a Horse Need?
The NRC (National Research Council, 2007) recommends a minimum of 40 mg of zinc per kilogram of dry matter intake for adult horses at maintenance. For a 500 kg horse eating around 10 kg of dry matter per day, that works out to roughly 400 mg of zinc per day as a bare minimum.
However, many equine nutritionists consider these NRC figures to be conservative. Practical recommendations often sit closer to 400–600 mg per day for a horse in light to moderate work, with higher levels for breeding, growing, or performance horses.
It's also worth noting that zinc needs to be considered alongside copper. The ideal zinc-to-copper ratio in the total diet is generally accepted to be around 3:1 to 4:1. Getting this ratio right is just as important as hitting the absolute numbers.
Why Do UK Diets Fall Short on Zinc?
This is the crux of the matter. There are several reasons why zinc deficiency is so widespread in UK horses, and most of them come down to the soil and forage our horses depend on.
UK Soils Are Naturally Low in Available Zinc
Much of the UK's agricultural land has soils that are either inherently low in zinc or have conditions that reduce zinc availability to plants. Alkaline and chalky soils — common across large parts of southern and eastern England — are particularly problematic because zinc becomes less available to plant roots as soil pH rises.
Even in areas where total soil zinc isn't especially low, factors like high phosphorus levels from fertiliser use and waterlogged conditions can further reduce uptake.
UK Grass and Hay Reflect the Soil
Because our soils are low in available zinc, the grass and hay grown on them is also low. Typical UK grass and hay contains somewhere between 15–30 mg of zinc per kg of dry matter — well below the 40 mg/kg minimum the NRC recommends.
This means that a horse eating nothing but UK pasture or hay is almost certainly getting only 50–75% of its minimum zinc requirement. And remember, the NRC figure is a minimum, not an optimum.
Conserved Forage Isn't Any Better
Whether your horse eats hay, haylage, or grass, the zinc content is determined by what was in the soil when the forage grew. Conserving forage doesn't add or concentrate zinc. If anything, some mineral losses can occur during the haymaking process through leaf shatter and leaching.
High Iron in UK Forages Compounds the Problem
Here's where it gets worse. UK pastures and forages tend to be very high in iron — often dramatically so. Iron is an antagonist to zinc (and copper) absorption. When dietary iron is excessive, it competes with zinc for absorption in the gut, effectively making an already marginal zinc intake even less useful to the horse.
It's not uncommon to see UK hay analyses showing iron levels of 200–500 mg/kg or more, against a requirement of only about 40 mg/kg. This iron overload doesn't just meet the horse's needs — it actively interferes with the absorption of the minerals the horse is already short of.
Hard Feeds and Balancers Don't Always Fix It
Many horse owners assume that feeding a commercial mix, cube, or balancer will automatically correct any mineral shortfalls. In some cases, it does help — but not always enough.
First, many horses are fed compound feeds at well below the manufacturer's recommended rate. If a feed is designed to be fed at 3 kg per day but your horse only gets 1 kg, you're only getting a third of the mineral supplementation the product was formulated to provide.
Second, not all balancers and supplements are created equal. Some contain zinc in forms that are poorly absorbed (such as zinc oxide), and the levels included may not be sufficient to overcome the combined challenge of low forage zinc and high forage iron.
Signs Your Horse May Be Low in Zinc
Zinc deficiency in horses is rarely dramatic or sudden. It's typically a chronic, low-grade insufficiency that manifests gradually. Signs to watch for include:
- Poor hoof quality — soft, crumbly, slow-growing, prone to cracks and chips
- Dull, harsh coat — slow to shed, lacking shine
- Skin problems — increased susceptibility to mud fever, rain scald, sweet itch, or slow wound healing
- Frequent low-grade infections — suggesting compromised immunity
- White line issues — poor hoof wall integrity at the white line
- Faded coat colour — particularly noticeable in dark-coated horses
- Poor growth in youngstock
Many of these signs are non-specific and could have other causes, which is part of why zinc deficiency so often goes unrecognised. The best way to know for certain is to look at the diet rather than the horse.
How to Assess Your Horse's Zinc Intake
Blood tests for zinc status in horses are unreliable. Serum zinc levels are tightly regulated and can appear normal even when body stores are depleted. The only truly accurate way to assess whether your horse is getting enough zinc is to analyse the whole diet.
This means knowing the mineral content of your forage — ideally through a forage analysis — and then adding up what your horse gets from forage, hard feed, and any supplements. When you compare the total intake against requirements, the shortfall (or surplus) becomes clear.
If you haven't done this before, analysing your horse's diet is the best first step. It takes the guesswork out of nutrition and tells you exactly where the gaps are — zinc included.
How to Supplement Zinc for Horses
Once you know your horse's diet is short on zinc (and it almost certainly is if you're feeding UK forage without targeted supplementation), the next step is choosing how to supplement.
Forms of Zinc
Not all zinc supplements are equal. Common forms include:
- Zinc sulphate — well absorbed, cost-effective, and widely available. This is a good all-round choice.
- Zinc chelate / zinc proteinate — zinc bound to amino acids, often marketed as more bioavailable. Good quality but more expensive.
- Zinc oxide — poorly absorbed compared to other forms. Often used in cheaper supplements because it's inexpensive, but it's not the best choice.
For most horses, zinc sulphate or a chelated zinc provides the best balance of efficacy and value.
How Much to Supplement
The amount you need to add depends entirely on what your horse is already getting from forage and feed. As a rough guide, most UK horses on a forage-based diet need an additional 150–300 mg of elemental zinc per day on top of what their forage provides, but this can vary significantly.
Always calculate based on elemental zinc content, not the weight of the compound. For example, zinc sulphate monohydrate is approximately 36% zinc by weight, so 1 gram of zinc sulphate provides about 360 mg of elemental zinc.
Don't Forget Copper
Whenever you supplement zinc, you need to ensure copper is also adequately supplied and that the zinc-to-copper ratio stays in the 3:1 to 4:1 range. Supplementing zinc alone, without attention to copper, can actually worsen a copper deficiency by further skewing the ratio.
UK forages are typically low in copper as well as zinc, so most horses need both supplemented.
Consider Iron Intake
If your horse has access to iron-rich water, iron-supplemented feeds (which are almost never necessary), or grazes on iron-rich soil, the effective absorption of supplemental zinc and copper will be reduced. In these cases, you may need to provide slightly higher levels of zinc and copper to compensate.
Common Mistakes When Supplementing Zinc
- Relying on a broad-spectrum supplement without checking the numbers. Many general-purpose supplements contain some zinc, but not nearly enough to correct a significant dietary shortfall.
- Feeding compound feeds below the recommended rate and assuming mineral needs are met.
- Supplementing zinc without copper. These two minerals must be considered together.
- Using zinc oxide when better-absorbed forms are available.
- Not getting forage tested. Without knowing what's in your forage, you're guessing — and guessing is how horses end up with chronic deficiencies.
Summary: Don't Overlook Zinc
Zinc is arguably the most under-appreciated mineral in UK equine nutrition. Our soils are low in it, our forages reflect that, and the high iron content of UK grass and hay makes matters worse by blocking absorption.
The consequences of chronic zinc deficiency — poor hooves, dull coats, weakened immunity, skin problems — are widespread and often attributed to other causes. Yet in many cases, correcting the diet is all that's needed.
The bottom line? If your horse is eating UK-grown forage and you haven't specifically addressed zinc (and copper) supplementation, there is a very high chance your horse is falling short. Get your forage tested, look at the total diet, and supplement accordingly. Your horse's hooves, coat, and immune system will thank you for it.