EquineHay Testing for Horses: Why It Matters and How to Do It
For most horses, hay is the biggest part of the diet by far, so what's in the hay shapes everything else. Two bales can look identical and be very different inside. A hay test is the only way to know what your horse is actually eating.
- Hay can vary widely in sugar, starch, protein and minerals, even from the same field.
- Sample 15–20 bales from one cutting with a hay probe for a reliable result.
- Ask for an equine package that includes ESC, WSC and starch, plus protein and minerals.
- Read results "as fed" for daily feeding math; use "dry matter" to compare hays.
- Share the report with your vet to decide on supplements, soaking or a different hay.
Why test your hay?
- Hay varies a lot. Sugar content depends on grass species, maturity at cutting, weather, time of day it was cut and how it dried. Grass hay commonly ranges from under 8% to over 18% sugar + starch.
- It's most of the diet. A 1,000 lb horse eating 20 lb of hay gets far more sugar, starch and protein from hay than from a few pounds of feed. See what NSC means.
- Sensitive horses need numbers. For insulin-resistant or laminitic horses, many vets want to know hay sugar before deciding on soaking or a different hay.
- It guides supplements. Knowing protein, copper, zinc and other minerals helps your vet decide whether a balancer or supplement is needed.
How to take a hay sample
A good sample represents the whole lot: hay from the same field and cutting, harvested under the same conditions.
- Get a hay probe. This is a hollow metal tube with a cutting tip that attaches to a drill. Many extension offices, feed stores and hay dealers lend them.
- Sample 15–20 bales chosen at random from the lot. For large round bales, sample fewer bales but from several sides.
- Drill into the cut end of small square bales (the side with the strings tied), 12–18 inches deep. For round bales, drill into the rounded side.
- Combine all cores in a clean zip-top bag. Don't sub-sample or pick out pieces.
- Squeeze out the air, seal and label the bag with the lot and date.
- Send it promptly to a forage lab.
A handful "grab sample" pulled from one flake isn't reliable, because leaves and stems separate and one bale may not represent the lot.
Which test to order
Labs offer packages. For horses, look for an equine package that includes:
- Dry matter (DM)
- Digestible energy (DE), usually in Mcal per lb or kg
- Crude protein (CP)
- ADF and NDF (fiber)
- ESC, WSC and starch: essential for metabolic horses
- Minerals: calcium, phosphorus, magnesium, potassium, and ideally copper, zinc, iron and manganese
Labs use two methods: NIR (near-infrared), which is faster and cheaper, and wet chemistry, which is generally more accurate, especially for minerals and sugars in unusual hays. Ask the lab which method suits your goals. Equine-focused forage labs and university labs are good places to start.
How to read a hay test report
Reports usually show two columns: as fed (or "as sampled") and dry matter.
- As fed includes the water in the hay. Use it for daily feeding math, since you weigh hay as fed.
- Dry matter removes the water. Use it to compare different hays fairly.
Example results (grass hay, as fed)
| Measure | Result | What it means |
|---|---|---|
| Dry matter | 90% | 10% water, typical for dry hay |
| DE | 0.85 Mcal/lb | Moderate energy |
| Crude protein | 9.5% | Typical for mature grass hay |
| ESC | 6.0% | ESC + starch = 8.0%; WSC + starch = 11.0% |
| WSC | 9.0% | |
| Starch | 2.0% | |
| Copper / Zinc | 6 / 22 ppm | Often low in grass hay |
Notice how much the NSC changes depending on whether you use ESC or WSC. Many vets use ESC + starch for metabolic horses; check which your vet prefers. You can enter your number in the Equine Feed Guide under "I have a hay test."
What about soaking hay?
Soaking hay in water removes some water-soluble sugars and can reduce dust. However:
- The amount of sugar removed varies widely between hays and soaking times.
- Soaking also removes some minerals, such as potassium.
- Soaked hay should be drained, fed promptly and not left to ferment, especially in warm weather.
Ask your vet whether soaking makes sense, and for how long. A hay test of soaked hay can show what's left.
How much does hay testing cost?
A basic NIR equine package often costs less than a bag or two of feed, and wet chemistry or mineral panels cost more. When you consider that the test covers months of hay, it's one of the most useful investments for a sensitive horse.
Frequently asked questions
How many bales should I sample for a hay test?
About 15–20 small square bales from the same lot, cored with a hay probe. For round bales, sample several bales from more than one side.
What is ESC and WSC in a hay test?
ESC is mostly simple sugars. WSC includes simple sugars plus fructans, so it's always equal to or higher than ESC. Many vets use ESC + starch for metabolic horses.
Should I use as-fed or dry matter results?
Use as-fed values for daily feeding math, since you weigh hay as fed. Use dry matter to compare different hays.
Does soaking hay remove sugar?
Soaking removes some sugar, but the amount varies widely. Ask your vet whether it suits your horse and how long to soak.
How often should I test hay?
Test each new lot or cutting. Hay from different fields or cuttings can be very different.
Sources and further reading
- University extension forage and horse programs on hay sampling and analysis (for example, Penn State and University of Kentucky).
- National Research Council. Nutrient Requirements of Horses, 6th revised edition (2007).
- Equine Endocrinology Group (EEG). Recommendations on forage carbohydrate targets for metabolic horses.
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