Carbohydrates in the Equine Diet

You know we can’t discuss equine nutrition without covering Carbs. Especially since Carbohydrates pretty much make up your horse’s entire diet including forages, grains, and by-products of forage and grain.

I want to keep it simple so you finish with a good understanding of what all the fuss is about regarding Carbohydrates. Carbohydrate (CHO) is the collective term for starches, sugars and fiber in your horse’s diet. If you are feeding correctly, this diet should be composed mostly of forage, as in grass, hay, haylage, beet pulp, etc. Forages provide the structural CHOs a horse can ferment well. Forages also provide a horse with some simple Carbs such as starch and sugar.

There are two kinds of Carbohydrates; Structural and Non-Structural.

It’s easy to remember which type comes from where if you think of the way a plant is designed. There is the part that gives it structure, like a skeleton of an animal. This would be the cell wall of the plant and thus contain the structural Carbohydrates cellulose, hemicellulose, pectin and the non-carbohydrate polymer lignin. The two main cell wall components, cellulose and hemicellulose, are also known as fiber.

These Carbohydrates cannot be broken down by enzymes in the small intestine and need to be fermented by microbes in the hind gut of the horse. Structural Carbohydrates are the major souce of energy to your horse when they are fermented they turn into Volatile Fatty Acids (VFAs) and gasses. The VFAs are used as energy for the horse, in fact VFAs provide as much as 30% of your horse’s total maintenance energy needs.

Lignin is also contained in the structural part of the plant but is not an actual Carbohydrate. As with the structural Carbs it also passes through to the hind gut but it cannot be broken down easily by fermentation. It not a good thing to have a high lignin content in your hay as it can actually bind to other CHOs and proteins reducing their availability to the horse. Lignin content increases as the planet matures so late cutting hay would be higher thus of lesser quality.

Sources of good Structural Carbohydrates (fiber) are pasture grass, quality hay, and beet pulp.

When we move to the inside of the plant cell, or the non-structural part, we find the Non-Structural Carbohydrates (NSC) stored for energy. An easy way to remember this is you put things inside for storage and NSCs are stored inside the planet cell.

NSCs are produced through photosynthesis, a process in which plants use sunlight and carbon dioxide to make sugar. Starch, comprised of a string of glucose molecules, is the primary energy source in most species of grasses, but some popular pasture plants also produce fructan, which consists of fructose and glucose.

As I have said, a diet high in good fiber, at the appropriate feeding rate for your horse, is the best choice as diets with too much starch and/or fructan is where the problems with Carbs begin.

NSCs (except fructans) are broken down by enzymes and absorbed in the small intestine. When too many are fed however, they are not all absorbed where they should be and end up in the hind gut which is designed to ferment structural carbohydrates.

Most horse owners have heard about starch, which is found in grains as well as growing plants, and know it is the most familiar culprit in Carbohydrate overload in horses. More recent research has been focusing on the effects of another danger in Carbohydrate overload and that is fructan.

Fructans, are sugars known as Water Soluble Carbohydrates (WSC) found in cool season grasses (think spring and fall). They are not digested and absorbed in the small intestine of the horse but pass through into the hind gut (or large intestine). Just as with starch too much of these little buggers will wreak havoc with your horse’s digestive process.

So if your horse’s diet has too many NSCs (sugar, starches and fructans) for the enzymes in the small intestine to break down and absorb, they will pass into the LI and the microbes there try to ferment them. When this happens the LI environment changes, VFAs are formed too quickly which increase lactic acid, the ph is lowered, the good fiber digesting microbes die, and are sent as poison to the blood stream. Your horse gets sick.

It’s best to keep it simple; horses are designed to digest/ferment fiber Carbohydrates in the large intestine (LI). If they do, the environment in the LI stays happy doing the job it is supposed to do. If things get into the LI that shouldn’t, the balance is upset and your horse gets sick.

When my clients ask about a “low-Carb” diet, they are usually really asking about a low NSC diet. Certain factors can influence the content of NSCs in the diet and horses vary in the degree of tolerance they have for higher levels of starches and sugars in their diet. You can see by the following chart that different feed stuff have differing levels of sugars and starches (NSCs) in them. Good commercial feed companies can also tell you what the NSC value is for their formulated feeds.

The greatest concern I see for “low Carb” diets in the insulin resistant or laminitic horse as well as the “easy-keepers”. What I tell these horse owners is that (in general), sugar can cause glucose and insulin surges that may trigger a problems in horses with abnormal glucose metabolism.

While most horses can graze on grasses high in NSC without a problem, owners with easy-keepers, insulin-resistant horses, horses with hormone imbalances and others at-risk for laminitis are wise to try reducing NSC in the diets they feed.

This can be difficult however because sugar levels within plants can fluctuate from hour to hour, time of year, plant type and soil fertility! There are certain things you can do though to become more aware of the NSCs in your horse’s diet and help control the intake.

Begin by having your pasture grasses and hay tested. Lab tests cannot isolate fructans, but they do measure it along with sugar and starch percentage as NSC. The goal with these horses would be to try to keep this number down to under 10%.

One way to do this is by practicing good pasture management. This includes regular mowing for those with good pastures, not letting pastures get too over grazed, using appropriate weed control, and proper fertilization.

If you are blessed with good pasture it’s best to keep your pasture mowed to a height of between four and eight inches to minimize the accumulation of Carbohydrates in pasture grasses.

Overgrazing or nutrient deficiencies can increase fructan levels in grasses so rest each field every two months. There is a misconception that shorter, sparse pastures don’t contain much sugar but that is not true. If you consider that the sugar content is usually highest during growth, then it’s easy to see why a pasture that is constantly trying to grow would contain sugar.

Over fertilization can be a problem as well. Be sure you are adding the correct amount of nutrients to your soil, so before you add additional fertilization, get a soil sample analysis.

In these sensitive horses and ponies limiting turn out (or no turn out) is sometimes the best thing you can do to control NSC intake. To me there are only two options if you want to control Carbs during turn out; using a grazing muzzle or a dry lot.

Grazing muzzles can restrict the amount of grass a horse grasps in one bite and this may be enough to protect a horse even when fructan levels rise. I usually suggest that these horses are turned out in the morning when fructan levels are lower, rather than late afternoon or early evening, especially during growing season.

Keeping sensitive horses in a dry lot with good forage and a slow feeder can also limit the risk of NSC overload. Slow feeders allow you to feed a low amount but they mimic the natural feeding pattern of a horse and thus won’t induce the stress that a very restrictive diet can induce.

Diets designed for feeding low amounts of soluble Carbohydrates include legume hay and concentrate feeds that have been formulated with beet pulp, soy hulls, rice bran. These feeds do not cause a change in blood glucose or insulin levels.

With all this being said, there are a group of horses that actually NEED a diet higher in NSCs. Medium level sugar and starch diets are acceptable for healthy horses that are working very hard and can metabolize glucose rapidly while exercising. These diets do not cause a problem in hard working horses because they are utilizing the NSCs and their metabolisms are functioning normally.

For example, a race horse or three day eventer can tolerate a diet with higher NSC value feedstuff such as corn, barley and oats due its increased need for energy. The short-duration horse or high-velocity performance horse will perform its work anaerobically using Carbohydrates readily. In general, higher energy density equals higher NSC values. The Carbohydrates from these grains (starches) are digested by enzymes in the small intestine and converted into glucose for readily available energy.

Providing high quality forage such as alfalfa and balancing with high energy sources such as fat and grain concentrates provide the fuel that these performance horses need.

A (very) simplistic analogy of humans to horses and Carb use would be the couch potato versus the marathon runner. A non-exercising, borderline diabetic human (IR, laminitic horse) needs to reduce his sugars while a fit marathon runner (performance horse) actually Carb loads before a race.

I could have made this very technical and there is a lot more you can learn about Carbohydrates in equine diets but my goal in this article was to share the “need-to-knows” and make this easy to understand. Here are some links to interesting research on Carbohydrates and horses.