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Starch vs. fiber - what is the difference?

Photo: Malgré Tout

We've talked at length about the issues with starch and sugar for horses. Especially the former, as horses don't actually digest starch very well and therefore it causes problems in both the stomach and appendix. This article aims to give you an overview of the major energizing nutrients and what they do for the horse.

Read also: Wrap vs. Hay - what is best?

About Martha Voss

Martha Voss is an equine agronomist and runs the independent consultancy and training company NENUC with courses, consultancy visits and development of learning games etc. Martha has more than 30 years of experience in teaching and research in horse husbandry and proper nutrition.


  • Carbohydrates
  • Fat
  • Protein


They all belong to the feed's "organic matter group". This means they can be metabolized in the horse's metabolism and burned for energy. What they have in common is that they consist of carbon, hydrogen, and oxygen coupled together with carbon as the skeleton, and oxygen and hydrogen in a specific system that determines which substance it is. They are formed in plants from the glucose produced in the leaves when the sun shines (photosynthesis). At night, the plant converts the many small glucose molecules into long carbon chains and thus into protein, fat, and carbohydrates.

Protein is a special group of substances as it also contains nitrogen linked in a so-called amino group. Protein is the building block of cells, but it is not so interesting as an energy source, as the amino group must be separated from the carbon skeleton for it to be burned in the cells. The amino group is converted into urine and excreted via the kidneys. This can be done, and if the horse is emaciated and has no more fat to burn, it can instead draw on the large protein depot in the muscles.

But it's a last resort because it's not an efficient source of energy. Protein is for building and maintaining body tissue, not for energy production in general. If your horse is struggling to gain weight, even if it's healthy and you're feeding it plenty of feed, it may have an excess of protein that it needs to excrete from the body as mentioned above, using energy from the feed that it would otherwise gain weight from.

If you are a little interested in chemistry, here are the chemical formulas of the mentioned energy nutrients. The picture of the amino acid shows the general formula. The attachment called R can vary and determines the character of the amino acid. Protein consists of long chains of different amino acids in different patterns, and they determine the character of the protein. Fat consists of three fatty acids, which are attached by a glycerol molecule. The three fatty acids can vary, depending on the character of the fat. All the substances on the left in the picture are different carbohydrates. Graphic: Martha Herold Voss.

On the other hand, carbohydrates and fats are excellent sources of energy. Fat is converted into fatty acids during digestion, which are then transported by the blood to the muscle cells. Here they are burned for energy or stored in the fatty tissue if there is a surplus to the horse's needs. From here, the horse can mobilize fatty acids again if it lacks energy. Some fatty acids are also used in various contexts and chemical tools in the body.

Fat is important in several parts of the body

  • The brain and nerve cells rely on fatty acids to function.
  • Some vitamins (A, D and E) are fat-soluble and need fatty acids to form.
  • Some hormones, including sex hormones, are made up of fatty acids.


Carbohydrates are a more complex group of substances and require a more detailed presentation.

The simplest carbohydrates include glucose. 6 carbon atoms in a ring with 6 oxygen atoms and 12 hydrogen atoms with the chemical formula C6H12O6. The nature of carbohydrates depends partly on how many hexagons are connected and how strong the bonds between the molecules are. Sugars are small molecules, while starch and fiber are long molecules.


Sugar consists of two glucose molecules of different kinds, such as coffee sugar, milk sugar, malt sugar, etc. During digestion, the sugar dissolves in the intestinal tract fluid and the digestive enzymes separate each sugar molecule into two glucose molecules. These are small enough to pass through the cells of the intestinal wall and into the blood, which transports the glucose around the body. The glucose in the blood is also called "blood sugar".


Starch consists of long, branched chains of glucose molecules. Like sugar, starch is a water-soluble carbohydrate and is broken down by digestive enzymes in the front part of the intestinal tract (stomach and small intestine) into glucose, which is absorbed into the blood. The digestibility of starch depends on what type it is. Oat starch is very easily digestible. This means that almost all oat starch can be digested in the small intestine, while starch from barley or corn, for example, must be heat-treated for enzymes to break it down. Therefore, starch residues often pass through the small intestine to the cecum. Here the starch encounters a large and complex population of microorganisms, including a group that loves starch.

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Photo: Malgré Tout

As they ferment the starch, they produce lactic acid as a waste product. The lactic acid is then converted into propionic acid, which is a short-chain fatty acid that can be absorbed into the bloodstream and used for energy like other fatty acids. If your horse needs food with a lot of energy in the form of starch, it's important to feed it in many small meals to prevent starch from reaching the intestinal bacteria. On the other hand, it's a good idea to add fiber-rich feedstuffs to the meal, either in the form of hay or wrap before the hard feed or as green pellets or beet pellets in the bucket. Fiber helps to stabilize the pH level of the digestive system.


Glucose is an important energy nutrient for the horse, as it is the main fuel in the body cells' energy production. But too much glucose in the blood is harmful. Among other things, the glucose molecules can bind to the blood cells, which causes the immune system to mistake them for foreign infectious agents and attack itself. This creates inflammatory conditions in the body and can cause allergies, for example.

That's why it's important to keep blood glucose levels appropriately low. If there is more glucose than the body cells need, the pancreas will produce the hormone insulin. Insulin is a key hormone as it goes into muscle and fat cells and opens their gates so that glucose can be stored in the cells, as glycogen or fat. If the cells are under the constant influence of insulin for a long time, the receptors that open the glucose gates wear out, making it harder for the horse to get glucose out of the blood. This condition is called insulin resistance and can be a contributing factor to laminitis.


Fibers are the longest and most tightly packed carbohydrates. It's a large group of substances, but roughly speaking it consists of soluble fibers (such as pectin) and insoluble fibers (such as cellulose). The horse's digestive system does not have the enzymes to break down the fibers, so they pass through the small intestine and into the cecum and colon, where they provide nutrient substrate for the microorganisms in this posterior intestinal section. Pectin fibers are interesting as they are easily fermentable by microorganisms and, like starch, they end up becoming propionic acid, but not with lactic acid as an intermediary. This means that there is no drop in pH in the cecum, which is why pectin fibers help stabilize the horse's digestion. Pectin comes from many fruits and beet pellets.


Cellulose fibers are found in both grass and straw. They are difficult to digest and the older the plant, the harder they are packed together. The horse has microorganisms that can break down cellulose, but it is a difficult task that takes a long time compared to the breakdown of pectin. For the microorganisms to ferment cellulose, they need energy, for example in the form of fatty acids from the pectin fibers and nitrogen from protein. The end products of the process are several short-chain fatty acids, acetic acid, and butyric acid. These are absorbed into the horse's bloodstream and used directly for energy production or stored as fat if there is a surplus. Fibre does not contribute directly to the horse's blood sugar pool and does not contribute to insulin production. The slow fermentation processes mean that the horse's blood values remain stable and it does not experience the fluctuations caused by sugar and starch.

Read more from Martha: Put your thin horse back in good shape


Both fatty acids from the fats in the feed and the fatty acids from the gut bacteria contribute to the horse's energy metabolism. Unlike glucose, which can be burned without oxygen, fatty acids always need oxygen in the cell to be burned. This means that the horse becomes calmer.

Trials with trotting horses in Sweden have shown that horses fed hay and beet pellets run just as fast as horses fed hay and oats. They get off to a slightly slower start, but they are more enduring.

The trials have formed the basis for recommendations to replace grain with beet fiber and alike also for sport horses. Several trials have shown that feeding high-quality, high-fiber feed to sport horses has no negative impact on blood counts and performance. In practice, it can be difficult to tell whether different feedstuffs provide fatty acids or glucose to the horse's body cells.

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I would recommend that you work with a skilled feed consultant who can help you optimize your horse's feeding plan according to its needs and the roughage it receives.


Jansson, A. & J.E. Linneberg 2012. A forage-only diet alters the metabolic response of horses in training. Animal

Richardson, K. & J.-A.M.D. Murray 2016. Fiber for performance horses: a review. Journal of Equine Veterinary Science


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