When we think of carbohydrates we often think of just starch and sugar, but actually fibre fits within this category as well. While fibre enjoys a very well-deserved reputation as the golden child of equine nutrition, starch and sugar are often considered to be red flags when reading feed labels or thinking about the nutrient content of forage.
Although starch and sugar are natural components of your horse’s diet, they have been linked to laminitis, Equine Metabolic Syndrome (EMS), obesity, and gastric ulcers. However, in appropriate amounts and in the context of the whole diet, they can provide a valuable nutritional contribution.
Types of carbohydrates
Fibre
Fibre is a type of carbohydrate that includes cellulose, hemicellulose and other structural carbohydrates found in plant cell walls. Unlike starch, which consists of glucose molecules arranged in branched or unbranched chains, cellulose consists of long chains of glucose molecules linked in a way that makes them resistant to digestion by the horse's own enzymes. Instead, fibre is fermented by microorganisms in the horse's hindgut, producing volatile fatty acids (VFAs), which can be absorbed and used as an energy source. Propionate, one of the main VFAs produced, can also contribute to glucose production in the liver through a process called gluconeogenesis. Fibre is generally digested more slowly than sugars and starches, providing a more sustained source of energy. Although the propionate can be converted to glucose, a sugar, the process by which that happens means a slow, low-level steady stream of glucose is available rather than a large amount at once.
Starch
Starch is mainly found in cereal grains, and in varying albeit small amounts in forage. It is made up of three or more sugar units linked together into branched chains. When digested, the horse’s enzymes break these links down and the resulting individual sugar units can then be absorbed in the small intestine in exactly the same way as simple sugars. If a large amount of starch is fed at once this process can happen quite quickly, releasing large amounts of sugar into the blood stream at once. This raises blood sugar levels quite substantially, and triggers the body to release insulin. Insulin acts as the key to unlock muscle and various other cells throughout the body so that the sugars can move from the blood into those cells where they are used to create energy.
Sugar
Sugar is found in feed ingredients like cereal grains and molasses, as well as grass and preserved forage. It is made up on only one or two sugar units, or molecules, and can be rapidly absorbed in the small intestine having the same impact on blood sugars and insulin levels described above.
What about fructan?
Carbohydrates are stored in grass as fructans. These are long chain molecules made up of lots of repeating fructose (a type of sugar) units. While the small intestine is perfectly capable of absorbing fructose, horses don’t have the enzyme necessary for breaking the chain links to release the fructose. Instead, the long chains of fructan go through to the hindgut undigested, and are then fermented by certain types of bacteria that form part of the gut microbiota. During that fermentation process lactic acid is produced, which lowers the pH of the hindgut and disrupts the delicate balance of the beneficial fibre-loving gut microbiota.
High levels of starches and sugars can also disrupt hindgut fermentation. If too much is eaten at once, they can overwhelm the digestion and absorption capacity of the stomach and small intestine, so move through to the hindgut undigested where they will be fermented by the resident bacteria. This can also lead to a drop in hindgut pH and imbalance in the microbiota, similar to that seen with fructans.
While cereal diets can be useful for some horses and ponies if fed appropriately, those with conditions such as Equine Metabolic Syndrome (EMS), Insulin Resistance (IR), Polysaccharide Storage Myopathy (PSSM), or prone to laminitis or “tying-up” are likely to need a diet with carefully controlled levels of starch and sugar.
How much starch and sugar is in the feed?
While the percentage of starch and sugar on the nutritional analysis is a great place to start, it doesn’t tell the full picture. The key piece of information is how much starch and sugar the horse is receiving from the feed, which will depend on both the percentage of starch and sugar, and also the quantity of the feed being given.
Looking at the percentages without putting it into the context of how much you’re feeding can be quite misleading, so it’s important to work out the actual amount fed, as shown below.
Weight in grams x (percentage nutrient ÷ 100) = amount of nutrient in grams in that amount of feed.
(Top tip, to work out the percentage ÷ 100, you can just move the decimal point to the left by two places, so 1% would become 0.01, 5% would become 0.05, 10% would become 0.1 etc.)
A low-calorie balancer that contains 6% starch and 2.5% sugar, with a feeding rate of 500g for a 500kg horse would provide:
Starch: 500 x 0.06 = 30g starch
Sugar: 500 x 0.025 = 12.5g sugar
While a concentrated, pelleted balancer that contains 23% starch and 9% sugar with a feeding rate of 40g for a 500kg horse would provide:
Starch: 40 x 0.23 = 9.2g starch
Sugar: 40 x 0.09 = 3.6g sugar.
So the balancer with the very low starch and sugar content delivers 42.5g starch and sugar combined, while the balancer with a very high starch and sugar content delivers only 12.8g starch and sugar combined.
These quantities are far lower than the amount that the horse will be taking in from forage and grass per day, but it does highlight the importance of working out what those percentages mean on an as fed basis, rather than looking at the percentage values on feed analysis on their own.
Summary
Carbohydrates are an integral and vital part of our horse’s diets, but the type of carbohydrate, timing, and total amount given per day will dictate how suitable the overall feeding strategy is for each individual horse.
If you would like any help working out a suitable diet for your horse, please don’t hesitate to reach out to our qualified nutrition team by email at [email protected], or give us a ring on 0800 585525.
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