NDF & ADF – How “rough” and how “digestible” is your roughage really?

When looking at a forage analysis, two numbers often appear that many overlook: NDF and ADF .
They don't tell you anything about the sugar content – ​​but they provide important information about structure, chewing time and the digestibility of the fibers .
Especially for frugal horses, it is valuable to understand the difference.

What does NDF mean?

👉 NDF (Neutral Detergent Fiber) is a measure of how “coarse” or “soft” the feed is.

• Low NDF → soft and easy to chew. The horse eats quickly, and the feed often contains more energy because there is usually also more sugar and easily digestible substances.
• High NDF → coarse and rich in structure. The horse chews longer, and the energy content depends mainly on the sugar and fiber quality - not just the number itself.

In short:
Low NDF = soft and high in energy
High NDF = roughage – energy depends on sugar and digestibility

Feed type	Typical NDF (%)	What does this mean in practice?
Straw	70–80%	Lots of structure – low energy and protein. Good employment for frugal horses.
Late harvested hay/wrap	60–70%	More structure and chewing time, often lower energy. Good for frugal horses if sugar is also low.
Normally harvested hay/wrap	50–60%	Often a good balance for many horses.
Early harvested hay/wrap	40–50%	Very soft and high in energy – good for horses with high needs, rarely suitable for frugal ones.

👉 50–65% NDF is usually good for most horses.

If NDF is too low (below about 45–50%)

• The horse finishes chewing quickly → longer breaks without feed
• Increased risk of stomach acid problems and boredom
• Often higher sugar and energy content → can cause overweight in frugal horses
• The intestinal flora has less “slow food” to work with

Solution: Supplement with structurally rich feed such as straw, and control the total amount carefully.

If NDF is too high (above approx. 70%)

• The horse chews a lot, but gets fewer calories and often too little protein if the feeding plan is not adapted.
• Risk of weight loss without supplementary feed
• Older horses and horses with dental problems may have difficulty utilizing very roughage.

High NDF is not dangerous – in fact, an advantage for frugal horses – but it requires a feeding plan with extra protein and minerals.

ADF – Fiber Digestibility

👉 ADF (Acid Detergent Fiber) tells us something about how much of the fiber is difficult to digest.
ADF consists mainly of cellulose and lignin – the higher the number, the lower the digestibility and energy yield.

• Low ADF → high digestibility, more energy per kg dry matter
• High ADF → lower digestibility, less energy

Feed type	Typical ADF (%)	What does this mean in practice?
Straw	45–55%	Very low digestibility – low energy
Late harvested hay/wrap	40–50%	Relatively low digestibility – often requires supplementation
Normally harvested hay/wrap	35–45%	Good balance between structure and energy
Early harvested hay/wrap	30–40%	High digestibility – very high in energy

As a rule of thumb:

• ADF < 40% → high energy content
• ADF 40–45% → medium
• ADF > 45–50% → low energy, low digestibility

Two feed analyses may have the same NDF, but very different ADF – i.e. same structure, but different energy utilization.

NDF and ADF say nothing about sugar

Both NDF and ADF are about fiber quantity and digestibility – not sugar content.
This means that a feed can have low NDF and ADF, but still have low sugar – or vice versa.

Therefore, you should always look at the sugar percentage separately, especially when feeding frugal horses or horses with metabolic diseases.

Energy content depends on several things

The energy content (EC) of roughage is influenced by many factors that interact:

1. Sugar and easily digestible carbohydrates – the more, the higher the energy
2. Fiber digestibility (ADF) – low ADF numbers provide higher energy
3. Fiber quantity and structure (NDF) – affects chewing time and satiety
4. Pectin and fermentable fiber – can contribute significantly to energy
5. Protein content – ​​plays a smaller role for energy than fiber/sugar, but is important for tissue building
6. Harvest time and plant maturity – young plants have lower ADF and higher energy than late harvested ones

Therefore, two analyses with the same NDF can give different energy, depending on ADF, sugar and harvest time.
And two analyses with the same sugar can give different energy if ADF and protein vary.

In short

• NDF tells how much chewing effort and structure the feed provides
• ADF tells how easy or difficult the fibers are to digest.
• Sugar must always be assessed separately
• The energy content depends on the combination of sugar, NDF, ADF, protein and harvest time.

Therefore, use all three numbers – sugar, NDF and ADF – together to get the best picture of the quality and suitability of the roughage for your horse.

Sources

1. Jansson, A. (2018). Forage intake and feeding behavior in horses. CLOSE.
2. Lindberg, J. E. (2012). Fiber in equine nutrition – effect on digestion and gut health. Animal Feed Science and Technology , 179(1–4), 123–132.
3. Muhonen, S. et al. (2009). Effects of feeding different forages on intake, chewing behavior and digestibility in horses. Livestock Science , 122(2–3), 214–221.
4. Harris, PA (1999). Nutritional management of horses and ponies prone to laminitis. Equine Veterinary Education , 11(4), 177–188.
5. Longland, AC et al. (2011). Pasture nonstructural carbohydrates and equine laminitis. Journal of Nutrition , 141(3), 778–783.
6. Ringmark, S. et al. (2015). Feeding straw as part of the forage ration to Standardbred horses in training. Animal , 9(11), 1959–1968.

✅ NDF = structure and chewing time
✅ ADF = digestibility and energy yield
✅ Sugar = glycemic load and energy contribution

Together they provide a complete picture of the properties of the roughage.