Grass Analysis for Horse Owners: What to Test & Why

Why Should Horse Owners Analyse Their Grass?

If your horse spends any significant time at pasture, grass is likely the single largest component of their diet — often making up 50–100% of total forage intake during the grazing season. Yet most horse owners have no idea what's actually in it.

We routinely analyse hay and haylage, and we carefully weigh out hard feed and balancers. But grass? It's just... there. Green, growing, and largely ignored from a nutritional standpoint.

This is a problem, because grass composition varies enormously depending on soil type, season, weather, grass species, fertiliser history, and pasture management. The mineral and sugar content of a field in Devon can be wildly different from a field in Yorkshire — and even the same field can change dramatically from April to October.

Grass analysis removes the guesswork. It tells you exactly what your horse is consuming and, more importantly, what might be missing — or present in excess.

What Does a Grass Analysis Actually Measure?

A good grass analysis report will typically cover the following categories. Let's break each one down so you know what you're looking at and why it matters.

Dry Matter (DM)

Fresh grass contains a lot of water — typically 70–85%. Dry matter is the percentage of the sample that remains once water is removed. All other nutrient values are usually expressed on a dry matter basis so they can be meaningfully compared to hay, haylage, and other feeds.

Why it matters: Dry matter tells you how much actual nutrition your horse is getting per kilogram of fresh grass consumed. A horse eating 50 kg of fresh grass at 20% dry matter is only consuming 10 kg of dry matter — the rest is water.

Crude Protein (CP)

Crude protein measures the total nitrogen content of the grass, multiplied by a standard factor to estimate protein. Spring grass can be surprisingly high in protein — sometimes 15–25% on a dry matter basis — while mature, stemmy summer grass may drop to 8–10%.

Why it matters: Most horses in light to moderate work don't need high-protein diets. Excess protein is broken down and excreted, placing extra load on the liver and kidneys and increasing ammonia in the stable. For horses prone to muscle problems or those with liver or kidney issues, knowing the protein level of their grass is essential.

Water-Soluble Carbohydrates (WSC) and Starch

WSC includes the simple sugars and fructans in grass. This is arguably the most important measurement for owners of horses and ponies prone to laminitis, equine metabolic syndrome (EMS), or insulin dysregulation.

WSC levels fluctuate dramatically with weather, time of day, and season. Cold, sunny days in spring and autumn can drive WSC levels dangerously high — sometimes above 25% DM — because the grass is photosynthesising rapidly but not growing fast enough to use up the sugars.

Why it matters: Horses with metabolic conditions can experience laminitis episodes when WSC intake is too high. Knowing your pasture's WSC levels helps you make informed decisions about turnout timing and duration. A single grass analysis won't capture all these fluctuations, but it gives you a baseline and helps you understand your field's tendencies.

Digestible Energy (DE)

Digestible energy is usually estimated from the other measured values and gives you an idea of the caloric density of the grass. Spring grass tends to be energy-dense; mature summer grass less so.

Why it matters: If your horse is gaining too much weight at pasture, knowing the energy content of the grass helps you make rational decisions about restricting intake, rather than just guessing.

Major Minerals

These are the minerals required in larger quantities:

• Calcium (Ca) — important for bones, muscle function, and nerve signalling
• Phosphorus (P) — works closely with calcium; the Ca:P ratio matters as much as the absolute amounts
• Magnesium (Mg) — involved in muscle and nerve function, often deficient in UK pastures
• Potassium (K) — usually abundant in grass, sometimes excessively so
• Sodium (Na) — almost always deficient in grass; horses need a salt source
• Chloride (Cl) — typically low in pasture
• Sulphur (S) — needed for hoof and coat quality

Why it matters: Mineral imbalances in grass directly affect your horse's health. For example, high potassium levels combined with low sodium and low magnesium — a very common UK pasture profile — can contribute to muscle tension, nervousness, and poor performance. Understanding these levels is the first step toward correcting them through targeted supplementation.

Trace Minerals

These are required in smaller amounts but are no less important:

• Iron (Fe) — almost always in excess in UK grass and soil. Rarely, if ever, needs supplementing.
• Zinc (Zn) — frequently deficient; essential for hoof quality, skin health, and immune function
• Copper (Cu) — frequently deficient; vital for connective tissue, coat colour, and iron metabolism
• Manganese (Mn) — usually adequate or high in grass
• Selenium (Se) — varies hugely by region; deficient in many UK soils
• Cobalt (Co) — needed for vitamin B12 synthesis by gut microbes
• Iodine (I) — not always included in grass analysis but important for thyroid function

Why it matters: The classic UK pasture pattern is high iron, low copper, and low zinc. Excess iron can interfere with the absorption of copper and zinc, compounding the problem. Without testing, you're just guessing — and most broad-spectrum supplements don't account for what's actually in your pasture.

How to Collect a Grass Sample

The accuracy of your results depends entirely on how well you collect the sample. Here's a step-by-step guide:

Step 1: Choose the Right Time

Aim to sample when conditions represent typical grazing. Avoid sampling immediately after heavy rain, fertiliser application, or a long dry spell — unless that's the norm for your field. For a general baseline, mid-season sampling (late May or June) works well. If you're concerned about sugar content in spring or autumn, sample during those specific risk periods.

Step 2: Walk a W Pattern

Don't just grab a handful from one spot. Walk a W or zigzag pattern across the field, collecting small snips of grass from 15–20 different points. This gives you a representative average rather than a snapshot of one unusual patch.

Step 3: Cut at Grazing Height

Cut the grass at the height your horse typically grazes — usually around 3–5 cm above ground level. Don't pull it up by the roots and don't cut it too high, or you'll misrepresent what the horse is actually eating.

Step 4: Mix and Bag

Combine all your snips in a clean plastic bag, mix them together, and then take a sub-sample of around 200–500 g (check your lab's requirements). Seal the bag, removing as much air as possible.

Step 5: Send Promptly

Fresh grass deteriorates quickly. Post your sample on the same day you collect it, using first-class or next-day delivery. Some labs prefer frozen samples — check their guidelines. Most UK equine labs will return results within 5–10 working days.

Where to Send Your Grass Sample

Several UK laboratories offer equine-specific grass and forage analysis. Popular options include:

• Equi-Analytical (via UK agents)
• NRM Laboratories
• Dairy One (US-based but widely used)
• Independent Equine Nutritionists who offer sampling kits and interpretation

Prices typically range from £30–£80 depending on the breadth of the analysis. A full mineral panel costs more but provides far more actionable data than a basic energy and protein screen.

How to Interpret Your Results

Getting a report back is one thing. Understanding it is another.

Here are some common patterns seen in UK grass analyses and what they mean for your horse:

High Iron, Low Copper, Low Zinc

This is extremely common across the UK. High soil iron locks up copper and zinc, and the grass reflects this. Horses on this pasture often show poor hoof quality, faded coats, skin issues, and compromised immunity. The solution is targeted copper and zinc supplementation — but at levels that account for the iron excess, which means higher doses than many off-the-shelf supplements provide.

High Potassium, Low Sodium, Low Magnesium

Another classic UK pattern, especially on heavily fertilised or clay-based soils. This imbalance can cause muscle tension, anxiety, poor sweating, and exercise intolerance. Adding a quality magnesium supplement and ensuring free-choice plain salt is available can make a significant difference.

High WSC

If your grass consistently tests above 10–12% WSC on a dry matter basis, you need to be cautious with metabolically sensitive horses. Consider strip grazing, grazing muzzles, turnout timing (early morning rather than afternoon), or reducing pasture access altogether.

Low Selenium

Many areas of the UK have selenium-deficient soils. Horses on these pastures may develop muscle stiffness, poor immune function, or reduced fertility. Selenium supplementation must be done carefully, as the margin between adequate and toxic is narrow. Always base selenium supplementation on tested levels.

Combining Grass Analysis with Your Horse's Full Diet

A grass analysis on its own is useful, but it becomes truly powerful when you combine it with analysis of your hay or haylage, any hard feeds, and supplements. Only then can you see the complete picture of what your horse is actually consuming versus what they need.

This is where analysing your horse's diet with a tool like MyEquiBalance becomes invaluable. By inputting your forage analysis data alongside everything else your horse eats, you can identify specific deficiencies and excesses — and make targeted adjustments rather than throwing a generic supplement at the problem and hoping for the best.

How Often Should You Test Your Grass?

As a minimum, testing once a year gives you a useful baseline. Ideally, you'd test:

• Once in spring (April/May) when growth is rapid and sugar levels tend to peak
• Once in mid-summer (July) when grass is more mature
• Once in autumn (September/October) when sugar and fructan levels can rise again

If you change fields, apply fertiliser, reseed, or notice significant changes in your horse's condition, an additional test is worthwhile.

Grass Analysis vs Soil Analysis: Do You Need Both?

Soil analysis tells you what's available in the ground. Grass analysis tells you what the plant has actually taken up. They don't always match — some minerals are present in soil but locked up in forms that plants can't access.

For horse owners, grass analysis is more directly useful because it reflects what your horse is actually eating. However, if you manage your own land and want to improve pasture quality long-term, a soil analysis can help guide liming, fertiliser, and over-seeding decisions.

Key Takeaways

• Grass is often the biggest component of your horse's diet — don't ignore it.
• Test for dry matter, protein, WSC, energy, major minerals, and trace minerals for a complete picture.
• Collect samples properly using a W pattern at grazing height for representative results.
• Common UK patterns include high iron with low copper and zinc, and high potassium with low magnesium — both of which can significantly affect your horse's health.
• Combine grass analysis with forage and feed analysis for a truly balanced diet.
• Test at least once a year, and more often if managing metabolically sensitive horses.

Grass analysis is one of the most cost-effective investments you can make in your horse's nutrition. For the price of a bag of feed, you gain the knowledge to make genuinely informed decisions about supplementation, turnout, and pasture management. It's not complicated, it's not expensive, and the insights it provides can transform your horse's health.