ADF and NDF in Hay: What They Mean for Your Horse

If you have ever looked at a hay analysis, you have probably seen ADF and NDF near the top of the report. Many horse owners skip right past them, but these two fibre numbers tell you a lot about how your horse will use that hay.

So, what is acid detergent fiber, and how is it different from neutral detergent fiber? In simple terms, ADF tells you how digestible the hay is, while NDF tells you how much of it your horse is likely to eat.

This guide explains both numbers in plain English, shows the ranges that are generally good for horses, and explains how to use them when comparing loads of hay in Alberta.

What Is Acid Detergent Fiber (ADF)?

Acid detergent fiber (ADF) is the least digestible part of the plant's fibre, made up mainly of cellulose and lignin. The higher the ADF, the less digestible the hay usually is.

Penn State Extension explains that ADF refers to cellulose and lignin, and that ADF is negatively correlated with digestibility. In other words, as ADF goes up, the share of the hay your horse can break down goes down.

Lignin is the woody part of the plant that horses cannot digest. As grass and alfalfa mature, they build more lignin and stems, so ADF tends to rise in later-cut, more mature hay.

What Is Neutral Detergent Fiber (NDF)?

Neutral detergent fiber (NDF) measures the total fibre in the plant's cell walls, including hemicellulose, cellulose and lignin. The higher the NDF, the less hay a horse is usually willing to eat.

Penn State Extension notes that NDF is negatively correlated with forage intake. Hay with very high NDF tends to be bulky and stemmy, and horses often eat less of it.

NDF is always higher than ADF on the same report, because NDF includes everything in ADF plus hemicellulose.

What Is the Difference Between ADF and NDF?

The simplest way to remember it: ADF is about digestibility, and NDF is about intake. Both go up as hay gets more mature.

Fibre Measure	What It Includes	What It Tells You	Higher Value Means
ADF (acid detergent fiber)	Cellulose + lignin	How digestible the hay is	Less digestible hay
NDF (neutral detergent fiber)	Hemicellulose + cellulose + lignin	How much a horse will eat	Horse likely eats less

Source: Penn State Extension

What Are Good ADF and NDF Levels for Horse Hay?

For most horses, hay with ADF in the 30s and NDF below about 65% is a good target. Hay above those levels is usually less digestible and less appealing.

Different extension sources give slightly different ranges. The table below compares guidelines from Penn State Extension and the University of Georgia Extension.

Test Value	Penn State Extension	University of Georgia Extension
ADF	Ideal range 30–45%; horses probably won't like hay above 45%	30–35% good; 35–40% moderate; over 40% poor
NDF	Ideal range 40–65%; horses probably won't eat hay above 65%	Above 65% tends to reduce intake

These are general guidelines, not strict cut-offs. A horse's needs, the rest of its diet, and the type of hay all affect what "good" looks like.

How Do ADF and NDF Differ Between Grass and Alfalfa Hay?

Grass hay usually has much higher NDF than alfalfa, while ADF can be similar. The University of Minnesota Extension gives these typical ranges.

Fibre Measure	Cool-Season Grass Hay	Legume Hay (e.g. Alfalfa)
ADF	30–40%	30–40%
NDF	55–65%	35–45%

This is one reason alfalfa is often more palatable than grass hay. It is also why you should compare grass hay with grass hay, and alfalfa with alfalfa, rather than judging every bale by the same NDF number.

For more on the two hay families, see our guides to timothy hay for horses and alfalfa hay for horses.

Why Do ADF and NDF Matter for Your Horse?

ADF and NDF help you predict how well your horse will eat and use a hay. That affects body condition, how much hay you need to buy, and how much ends up wasted.

Hay with high ADF gives your horse less usable energy per bale. A horse eating that hay may need more of it, or extra feed, to hold condition.

Hay with high NDF may be eaten more slowly or left behind. That can be helpful for some easy keepers, but it can be a problem for hard keepers and seniors who need to eat more.

Which Horses Do Well on Higher-Fibre Hay?

Easy keepers and horses at maintenance often do fine on hay with moderate to higher fibre levels. It lets them chew for longer without taking in too many calories.

The University of Georgia Extension suggests later-cut, more fibrous hay for metabolic horses and easy keepers, while still staying within upper ADF and NDF limits to avoid digestive issues.

Which Horses Need Lower-Fibre Hay?

Hard keepers, senior horses, growing horses, broodmares and horses in heavy work usually need more digestible hay with lower ADF and NDF. Early-cut, leafy hay generally fits better.

For older horses, see our guide to the best senior horse feeds. For horses that need to gain weight, see the best horse feed for weight gain.

How Do ADF and NDF Relate to TDN and RFV on a Hay Report?

Many labs use ADF and NDF to calculate other values on your report, such as TDN (an energy estimate) and RFV (a quality index). Knowing this helps you read the whole report.

What Is TDN?

TDN (total digestible nutrients) is an estimate of the energy in the hay. Most labs do not measure energy directly. They calculate it from ADF.

Alberta Agriculture's feed testing FAQ gives this equation for legume, grass and mixed hays: TDN (%) = 88.9 – (0.779 × ADF%). The table below shows what that equation gives at a few ADF levels.

ADF (%)	Estimated TDN (%) Using Alberta Agriculture Equation
30	About 65.5
35	About 61.6
40	About 57.7

The pattern is clear: as ADF rises, estimated energy falls. Keep in mind that TDN is an estimate calculated from ADF, so treat it as a rough guide rather than an exact energy value for your horse.

What Is RFV, and Does It Work for Horse Hay?

Relative Feed Value (RFV) is a quality index calculated from ADF and NDF. A higher RFV means higher quality.

Alberta Agriculture lists an RFV of about 100–115 as suitable for idle horses. However, it also warns that RFV is not a reliable measure for mixed hay, grass hay or cereal greenfeed, because it works best for pure alfalfa.

The University of Georgia Extension suggests Relative Forage Quality (RFQ) of about 100–130 for maintenance horses and 130+ for growing, lactating or performance horses.

How Does Hay Maturity Change ADF and NDF?

As hay plants mature, they grow more stem and less leaf, and their fibre becomes less digestible. That means ADF and NDF both tend to rise the later the hay is cut.

The University of Minnesota Extension notes that plants have more fibre and less protein as they mature, while young, immature plants are more nutrient-dense and lower in fibre.

This is why first and second cut hay can test so differently. Our guide to the differences between 1st and 2nd cut timothy hay explains more.

How Do You Get Your Hay Tested?

To get reliable ADF and NDF numbers, you need a good sample. A single handful from one bale will not represent a whole load.

The Alabama Cooperative Extension System recommends these basic steps:

•       Test by lot. A lot is hay harvested at the same time, from the same field, under the same conditions.

•       Use a hay probe. Take 15 to 20 core samples from different bales in the lot.

•       Sample the right spot. Insert the probe at a 90-degree angle, into the curved side of round bales or the centre of the end of square bales.

•       Mix and bag. Combine the cores, place them in a sealed plastic bag, and label it.

Before you buy, ask your supplier whether a hay analysis is available for the lot. Our guide to reading a hay analysis report explains the other numbers you will see, such as moisture, protein and NSC.

Should You Read the "As Fed" or "Dry Matter" Column?

Use the dry matter (DM) column when comparing hays. Penn State Extension explains that dry matter values remove the water, so you can compare different hays on equal footing.

The "as fed" column shows nutrients in the hay as it actually is, including moisture. It is useful for working out how much to feed, but not for comparing quality between loads.

What Mistakes Do Owners Make When Reading ADF and NDF?

The most common mistakes are judging hay by one number, comparing grass and alfalfa on the same scale, and mixing up dry matter and as-fed values.

•       Looking only at protein. ADF and NDF tell you how usable that protein and energy really are.

•       Comparing grass hay NDF with alfalfa NDF. Grass is naturally higher in NDF.

•       Relying on RFV for grass hay. Alberta Agriculture notes RFV is not reliable for grass hay.

•       Mixing as-fed and dry matter numbers. Compare hays on a dry matter basis.

•       Testing one bale for a whole load. Core 15 to 20 bales from the same lot.

•       Ignoring sugar for sensitive horses. ADF and NDF do not tell you NSC; check that separately.

For horses that need low-sugar hay, see our guide to low-sugar hay for horses.

Where Can You Find Tested Horse Hay in Alberta?

Horse Creek Hay & Feed supplies horse hay from Rocky View County near Cochrane, serving Calgary, Edmonton and surrounding Alberta areas. Our 2026 hay collection includes timothy, timothy/alfalfa and grass/alfalfa hays from local growers.

Not sure how to read your hay report? Our in-house equine nutritionist can help match a hay analysis to your horse's needs through our nutrition service.

You can also contact our team to ask about current lots or arrange delivery. [FILL IN: which current hay lots have ADF/NDF results available]

Conclusion

ADF and NDF are two of the most useful numbers on a hay analysis. ADF tells you how digestible the hay is, and NDF tells you how much your horse is likely to eat.

For most horses, hay with ADF in the 30s and NDF under about 65% is a good place to start. Easy keepers can often handle more fibre, while seniors, hard keepers and working horses usually need more digestible hay.

Use these numbers alongside protein, sugar and a visual check of the hay. If you are unsure what your horse needs, ask an equine nutritionist or your veterinarian.

Frequently Asked Questions

Is lower ADF always better for horses?

Not always. Lower ADF means more digestible hay, which suits hard keepers and working horses. But easy keepers may gain too much weight on very digestible hay, so a slightly higher ADF can be a better fit for them.

Can I tell ADF and NDF just by looking at hay?

Not accurately. Stemmy, coarse hay usually has higher fibre, and leafy, fine hay usually has lower fibre. A lab test is the only way to know the actual numbers.

Why is my grass hay NDF higher than my alfalfa hay?

Grass hays naturally have more cell-wall fibre than legumes like alfalfa. University of Minnesota Extension lists typical NDF of about 55–65% for cool-season grass hay and 35–45% for legume hay, so a higher number in grass hay is normal.

Does soaking hay change ADF and NDF?

Soaking is used mainly to reduce sugar and dust, not to change fibre. If you need exact numbers for soaked hay, ask your lab or an equine nutritionist. See our guide on whether soaking hay reduces sugar.

How often should I test my hay?

Test each new lot of hay, since hay from different fields, cuttings or years can vary a lot. If you buy a full winter's supply from one lot, one good sample is usually enough for that lot.