Fibre is routinely underestimated. That is a shame, because it forms the basis of every healthy equine ration. In this episode Maartje explains what fibre is and what happens to it in the digestive tract.

Short answer

Fibre consists of structural carbohydrates that a horse cannot break down with its own enzymes. Bacteria in the caecum and large intestine ferment them into volatile fatty acids, a source of slow-release energy. Sugar and starch are the other category: the horse digests those itself, using enzymes in the small intestine, which gives fast-release energy.

Which types of carbohydrate does a horse deal with?

Look at the equine digestive system and carbohydrates fall into two categories.

Category 1 – carbohydrates the horse digests itself. This covers sugar and starch. The horse breaks them down with enzymes in the small intestine and absorbs the building blocks there. The result is quickly available energy.

Category 2 – structural carbohydrates. This is fibre. The horse has no enzymes capable of breaking it down, so it passes through to the caecum and large intestine largely unchanged.

What happens to fibre in the hindgut?

The caecum and large intestine hold a large bacterial population. Those bacteria break fibre down by fermentation, and the end products of that process are something the horse can absorb: volatile fatty acids.

Those volatile fatty acids are the reason fibre counts as a source of slow-release energy. The energy is released gradually rather than in a spike. For a horse that needs to perform consistently – or that should not become sharper – this is exactly what you want.

Why does this distinction matter in practice?

Because it determines how your horse responds to its feed.

• A ration high in sugar and starch produces peaks in blood glucose and can make some horses sharper.
• A fibre-based ration delivers energy more evenly and keeps the gut microbiota more stable.

So the question is not only how much energy you feed, but what kind.

There is a practical consequence too. Because fibre is fermented slowly, a horse eating a fibre-based ration keeps a more constant supply of energy between meals. You are feeding a system that works continuously rather than in bursts.

How do you recognise a fibre-rich product?

Check the label for the crude fibre content. It gives a good indication of how much fibre a product contains. As a rule of thumb: the higher the crude fibre content, the more fibre-rich the product. Products at around 20% crude fibre or more are generally a good source of fibre.

Compare that with a typical concentrate, where the crude fibre figure is usually far lower. The label tells you which side of the line a product sits on before you ever open the bag.

Frequently asked questions

What exactly are structural carbohydrates? Structural carbohydrates are the carbohydrates that make up a plant’s cell wall, such as cellulose and hemicellulose. They give the plant its rigidity, and for the horse they are only available through bacterial fermentation.

What are volatile fatty acids in horses? Volatile fatty acids (acetic, propionic and butyric acid) are the end products of fibre fermentation in the hindgut. They supply a substantial share of a horse’s daily energy.

Are sugar and starch bad for a horse? Not by definition. What matters is the amount per meal and how it is spread across the day. Episode 3 covers this.

Where is most of the fibre found? In forage: hay, haylage, grass, lucerne, forage mixes and forage pellets. Concentrate generally contains far less fibre.

Sources

• Merck Veterinary Manual – Digestive System of Horses / Nutritional Requirements: https://www.merckvetmanual.com/management-and-nutrition/nutrition-horses/nutritional-requirements-of-horses-and-other-equids