Grass Analysis for Horse Owners: What to Test & Why

Why Every Horse Owner Should Consider Grass Analysis

Grass is the foundation of most horses' diets. Whether your horse lives out 24/7 or spends a few hours a day on pasture, the nutrients in that grass — or the lack of them — have a huge impact on health, weight, hoof quality, coat condition, and even behaviour.

Yet most horse owners have no idea what their grass actually contains.

A grass analysis gives you hard data instead of guesswork. It tells you exactly what your pasture is providing and, critically, what it isn't. Armed with this information, you can make informed decisions about supplementation, hard feed, and overall diet management.

In this guide, we'll walk through what a grass analysis tests for, why each parameter matters, how to collect a proper sample, and how to put the results to practical use.

What Is a Grass Analysis?

A grass analysis is a laboratory test performed on a sample of pasture (or hay, haylage, or any forage) that breaks down its nutritional composition. The lab report typically includes values for energy, protein, fibre, sugars, minerals, and trace elements.

Think of it as a nutritional label for your field. Just as you'd read the label on a bag of feed, a grass analysis tells you what your horse is actually eating when it grazes.

What to Test: The Key Parameters Explained

Dry Matter (DM)

Dry matter is the percentage of the sample that remains after all water is removed. Fresh grass can be 75–85% water, meaning only 15–25% is actual nutrition.

Why it matters: All other nutrient values are usually expressed on a dry matter basis. Without knowing the dry matter content, you can't accurately calculate how much of each nutrient your horse is consuming per kilogram of grass eaten.

Digestible Energy (DE)

Digestible energy is measured in megajoules per kilogram of dry matter (MJ/kg DM). It tells you how much usable energy the grass provides.

Why it matters: Energy is the primary driver of weight gain or loss. Lush spring grass can have a surprisingly high energy content — sometimes rivalling a moderate hard feed. Knowing the energy value helps you manage weight, particularly in good doers or horses prone to obesity.

Crude Protein (CP)

Crude protein is the total protein content of the grass, expressed as a percentage of dry matter.

Why it matters: Protein is essential for muscle development, tissue repair, hoof growth, and immune function. Spring and early summer grass is often high in protein, while mature or winter grass can be low. Knowing the protein content helps you judge whether your horse needs additional protein from hard feed or a balancer.

Water-Soluble Carbohydrates (WSC) and Starch

WSC includes simple sugars and fructans — the carbohydrates most relevant to laminitis risk. Some labs also report ethanol-soluble carbohydrates (ESC) separately, which represent the simple sugar fraction alone.

Why it matters: This is arguably the most important value for owners of laminitis-prone horses, those with Equine Metabolic Syndrome (EMS), or horses with Pituitary Pars Intermedia Dysfunction (PPID/Cushing's). High WSC levels in grass are a well-known laminitis trigger. Knowing when your pasture sugar levels spike allows you to manage grazing times and turnout more safely.

As a general guideline, a combined WSC + starch value below 10% DM is often recommended for metabolically sensitive horses, though individual thresholds vary.

Neutral Detergent Fibre (NDF) and Acid Detergent Fibre (ADF)

NDF represents the total fibre content (cellulose, hemicellulose, and lignin), while ADF is a measure of the less digestible fibre fraction (cellulose and lignin).

Why it matters: Fibre is the backbone of equine gut health. Higher NDF values generally mean the grass is more mature and less digestible, which can actually be beneficial for overweight horses — it provides gut fill with fewer calories. Lower NDF values indicate younger, more digestible (and often more calorific) grass.

Major Minerals: Calcium, Phosphorus, Magnesium, Sodium, Potassium

These are the macro-minerals your horse needs in the largest quantities.

Why they matter:

• Calcium and Phosphorus — The calcium-to-phosphorus ratio is crucial for bone health. Ideally, the diet should provide a Ca:P ratio between 1.5:1 and 2:1. UK and Irish pastures are often adequate in calcium but can vary significantly depending on soil type.
• Magnesium — Important for muscle and nerve function. Grass is frequently low in magnesium, and deficiency has been linked to nervous behaviour, muscle tension, and grass tetany.
• Sodium — Almost always deficient in grass. Horses in work especially need supplemental sodium (salt).
• Potassium — Usually abundant in fresh grass, sometimes excessively so. Very high potassium can interfere with magnesium absorption.

Trace Elements: Copper, Zinc, Manganese, Iron, Selenium, Cobalt, Iodine

Trace elements are needed in tiny amounts but are absolutely vital for health.

Why they matter:

• Copper and Zinc — Frequently deficient in UK and European pastures. Both are essential for hoof quality, coat condition, immune function, connective tissue integrity, and coat colour (copper especially). A common finding is that grass provides only a fraction of the horse's daily requirement.
• Iron — Almost always present in excess in grass and soil. Excessive iron can interfere with copper and zinc absorption, compounding existing deficiencies.
• Selenium — Deficient in many UK soils and therefore in the grass that grows on them. Selenium is a powerful antioxidant and essential for muscle function. However, the margin between adequate and toxic levels is narrow, so supplementation should be guided by data.
• Manganese — Usually adequate or high in grass, but worth confirming.
• Cobalt and Iodine — Often low and sometimes overlooked. Cobalt is needed for vitamin B12 synthesis in the hindgut, while iodine supports thyroid function.

How to Collect a Grass Sample

Getting a representative sample is important. A poorly collected sample gives misleading results.

Step-by-Step Method

1. Walk a W pattern across your field, collecting small handfuls of grass at 15–20 points along the way.
2. Cut the grass at grazing height — roughly 3–5 cm above the ground. This represents what the horse actually eats, not the entire plant including the base it leaves behind.
3. Avoid areas near gateways, water troughs, or dung patches — these are not representative of general grazing.
4. Mix all samples together in a clean plastic bag and send approximately 300–500g to the lab.
5. Send quickly — ideally within 24 hours. Some labs recommend refrigerating (not freezing) the sample if you can't post it immediately.

When to Test

Grass composition changes throughout the year, so a single test only gives you a snapshot. Ideally, test:

• Spring (April–May) — when sugar and protein levels tend to peak.
• Mid-summer (July–August) — when grass may become more fibrous.
• Autumn (September–October) — when a second flush of growth can increase sugar levels.
• Winter — if horses are still grazing standing grass.

Even a single test is far better than none. If budget is a concern, spring is the most valuable time to test, as this is when laminitis risk and nutritional extremes tend to be highest.

Understanding Your Results: Common Patterns in UK and European Pastures

While every field is different, grass analyses across the UK and Ireland frequently reveal similar patterns:

• High iron, high potassium — very common, especially on heavier soils.
• Low copper, low zinc — the single most consistent finding. Horses on grass alone almost never get enough of these trace elements.
• Low sodium — virtually universal. Horses need supplemental salt.
• Variable selenium — can be very low depending on your region.
• High WSC in spring and autumn — especially on ryegrass-dominant pastures.
• Adequate to high protein in spring — dropping significantly in winter.

These patterns explain why a broad-spectrum vitamin and mineral supplement or feed balancer is almost always necessary, even when grass appears lush and plentiful.

Putting Your Grass Analysis to Work

Having data is only useful if you act on it. Here's how to translate your grass analysis into practical diet decisions:

1. Calculate Total Nutrient Intake

Estimate how much grass your horse eats per day (on a dry matter basis). A horse on full-time turnout may consume 2–2.5% of its body weight in dry matter daily. Multiply this by the nutrient percentages on your grass analysis to estimate daily intake of each nutrient.

2. Compare Against Requirements

Compare your horse's estimated intake against established nutrient requirements (such as those published by the NRC). This reveals gaps — and surpluses.

3. Fill the Gaps with Targeted Supplementation

Rather than throwing a generic supplement at the problem, use your analysis to choose products that address your specific shortfalls. For instance, if copper and zinc are very low but iron is high, you'd want a supplement that provides copper and zinc without adding unnecessary iron.

4. Analyse the Whole Diet

Grass is only one part of the picture. Your horse may also receive hay, haylage, hard feed, a balancer, and supplements. All of these contribute to total nutrient intake. For the most accurate picture, consider analysing your horse's complete diet to see how pasture intake fits alongside everything else your horse receives. This whole-diet approach is far more effective than adjusting individual components in isolation.

5. Retest and Adjust

As grass composition changes with the seasons, so should your feeding plan. A grass analysis from May won't accurately represent what your pasture provides in November. Periodic retesting keeps your data — and your decisions — current.

Grass Analysis vs. Hay Analysis: Do You Need Both?

In short, yes — if your horse eats both. Hay and grass from the same field can have very different nutritional profiles because the nutrient content changes with maturity and is affected by the drying and curing process. Hay analysis is particularly important because conserved forage often forms the bulk of the winter diet.

However, if you can only afford one test, prioritise whichever forage makes up the largest portion of your horse's diet at the time.

Where to Get Your Grass Analysed

Several laboratories in the UK offer equine-specific forage analysis, including:

• Equi-Analytical services from forage testing labs
• Independent agricultural labs that offer mineral and nutritional panels
• Some feed companies that offer forage analysis as part of their advisory services

Expect to pay between £25 and £80 depending on the panel you choose. A full mineral and nutritional analysis is the most useful option. The relatively small cost is trivial compared to the savings you can make by supplementing accurately rather than guessing.

Frequently Asked Questions

Is grass analysis worth it for leisure horses?

Absolutely. Leisure horses are just as susceptible to mineral deficiencies, laminitis, and weight issues as competition horses. In fact, because leisure horses often receive fewer hard feeds (and therefore fewer added nutrients), knowing what the grass provides is arguably even more important.

Can I just test my soil instead?

Soil tests are useful for land management, but soil mineral content doesn't always correlate directly with what ends up in the grass. Plants absorb minerals selectively, and factors like soil pH, drainage, and grass species all influence uptake. A direct grass analysis is far more relevant for nutritional planning.

Does the type of grass matter?

Yes. Ryegrass-dominant pastures tend to have higher sugar content than mixed or native-species pastures. If you know your pasture composition, it adds context to your analysis results.

Final Thoughts

A grass analysis removes the guesswork from your horse's diet. For a modest investment of time and money, you gain a clear understanding of what your pasture provides — and, just as importantly, what it doesn't.

Armed with this knowledge, you can supplement with precision, manage laminitis risk more effectively, and give your horse the balanced diet it deserves. Whether you own one horse on a small paddock or manage a large yard, testing your grass is one of the smartest nutritional decisions you can make.