Why Diets Low in Starch Are So Beneficial
Diets low in non-structural carbohydrates are a better and more natural choice for horses. Providing your horse with a feed that is low in starch minimizes the risk of laminitis, colic, tying-up, developmental orthopedic diseases, hyperactivity, insulin resistance and other nutritionally related disorders in horses. But why?
Click on each of the subject headings to find out.
The Equine Digestive System
The horse has evolved over millions of years as a grazing herbivore. Ancestors of the modern horse roamed vast distances everyday, grazing on a diet of grass, shrubs and herbs, much as zebras do today. The horse has adapted its behavior and digestive system to survive in this environment. Consequently, an understanding of the horse's natural eating patterns, feeding behavior and digestive function is essential for maintaining a healthy and happy horse.
The horse is a monogastric herbivore; Simply put the horse has one stomach and eats plants. When the horse eats, digestion begins as the food is masticated (chewed) and then swallowed - permitting food to pass down the esophagus and into the stomach. The stomach and small intestine are collectively called the foregut. It is in the foregut that the digestion of starches and sugars take place. After about 1 hour, the contents of the foregut enter the hind gut (or large intestine), which is made up of the cecum and the colon. The hind gut is the largest part of the equine digestive tract and it is where fibers are digested.
About Carbohydrates
Carbohydrates are the collective name given to the starches, sugars and dietary fibers that can be digested in some form to provide energy. Carbohydrates fall into one of two categories, structural (or complex) carbohydrates and non-structural (or simple) carbohydrates. When we refer to low carbohydrate in horse nutrition, what we really mean is low "non-structural" carbohydrate.
Non-structural carbohydrates (NSC) are starches and simple sugars. These can be broken down by enzymes that the horse itself can produce in the small intestine. The end-products of their digestion are sugars, which are absorbed from the small intestine and used for energy. This energy is rapidly available to the horse, and is often referred to as quick-release or "heating" type energy, and has been used to explain why some horses become excitable on grain based or high-starch diets.
Structural carbohydrates are dietary fibers and describe those carbohydrates that give "structure" to plants or protective coats to seeds. Fiber itself is made up of a mixture of different complex carbohydrates, known as cellulose and hemi-cellulose, bound together with some non-carbohydrate materials such as lignin.Cellulose and hemi-cellulose cannot be broken down by the horse's own enzymes. Alternatively, the horse relies on microbes in its hindgut to break down the cellulose and hemi-cellulose from plant material, this process is known as fermentation. Hence, the horse is referred to as hindgut fermenter.
In fact the horses' digestive tract has 65% of its volume dedicated to the fermentation and absorption of nutrients from fiber. This area is the hindgut and is made up of the cecum and the colon. It is in the cecum where the majority of the fiber-fermenting microbes are present. The microbes break down the strong cellulose bonds and produce volatile fatty acids or VFA's. These end products of fermentation are then absorbed and are either converted into glucose or fat, or used directly as an important energy (or calorie) source for the horse.
Fiber is often termed as a "slow-release energy" source, as the process of digesting fiber is relatively slow when compared to that of non-structural carbohydrates. Therefore, energy from fiber is less likely to cause excitability than energy from sugars and starch.
About Fiber
Fiber is often termed as a "slow-release energy" source, as the process of digesting fiber is relatively slow when compared to that of non-structural carbohydrates. Therefore, energy from fiber is less likely to cause excitability than energy from sugars and starch.
Fiber makes up a large proportion of the horses' natural diet; it is found in grasses, hays, chaffs and some horse feeds. Often people dismiss fiber as bulk, but it is an important nutrient source for the horse. But nNot all fibers are highly digestible to the horse. Some high fiber ingredients are readily fermented and digested while other ingredients have high levels of lignin fiber that is considered indigestible. Beet Pulp and soybean hulls are examples of ingredients that are high in good quality, digestible fiber.
After water, fiber is the most important component of the diet for any horse. The horse has evolved to eat fiber, and although a modern thoroughbred may be a far cry from its distant ancestors, its digestive physiology remains one that is best suited to a high fiber diet. But, not only does the horse have a physical need for fiber to maintain his digestive function, he also has a psychological need to chew. In the wild or turned out with free access to pasture, a horse will eat for approximately 16-18 hours per day.
Why Control the Sugars and Starches in Your Horse's Diet?
Digestion
The horse's small intestine is relatively short and is the only part of the digestive tract where starch and sugar can be digested and absorbed by the horse's own enzymes. Any starch that remains undigested passes through into the hindgut where it can cause starch-overload. This happens as the undigested starch is fermented in the hindgut by the microbes that normally break down fiber. The end product of this starch fermentation is lactic acid, rather than volatile fatty acids, as it is with fiber. This lactic acid acidifies the gut environment. As the pH drops, certain fiber fermenting bacteria are killed as they cannot tolerate the more acidic environment. Even a partial starch-overload can cause a disruption to hindgut fermentation, leading to digestive upsets, which may include in a mild case - loose droppings, and in the worst case - fatal colic.
Gastric health
Performance horses that are managed and trained intensively often have restricted amounts of fiber in their diet and are usually given feeds that are high in sugar and starch. This means there are times when the stomach is empty and excess acid can come directly in contact with the stomach wall where ulcers can then develop. Starch in grains can also add to the problem by stimulating gastrin, a hormone that promotes stomach acid production. Starch can also be fermented in the stomach of the horse to form strong acids that can again attack the unprotected upper regions of the stomach.
Behavior/Hyperactivity
The effect energy has on a horse depends largely on its genetic make up and temperament. For some, feed is a fuel injection, but for others no amount of food can provide the necessary motivation for anything active. Feeds that excite horses are commonly said to be "heating" and those that don't, "non-heating."
Diets high in starch and sugar can generate a "heating effect." Corn, for instance, has a reputation of heating horses up. Fiber on the other hand is digested more slowly, and the end products of digestion are released more gradually, resulting in a constant, "slow-release" energy rather than a sudden rush of energy. The term "non-heating" is therefore applied to many high fiber feeds.
Insulin Resistance/Laminitis
The most common cause of nutritionally induced laminitis is an overload of rapidly fermentable carbohydrate either from starch found in grains and plants or sugars and fructan found in grass. In addition to this direct effect, recent research has suggested that the long term feeding of sugar and starch based feeds may lead to changes in glucose metabolism resulting in insulin resistance. Recently, insulin resistance has been identified as having a role in the development of laminitis.The current advice on managing laminitis is to restrict access to pasture at times of rapid grass growth and avoid grains and high-starch feeds. Alternatively choose feeds based on fiber and fat with low levels of sugar and starch.
Recurrent Exertional Rhabdomolysis (RER) or Tying-Up
High starch diets have also been implicated as a high risk factor in the development of RER. Therefore, horses suffering from RER require a restricted intake of starch, which needs to be individually tailored, along with the amount of work required, for each individual horse. Management includes reducing stress and promoting calm behaviour; maintaining exercise and avoiding stall rest whenever possible, while decreasing the intake of starches and utilizing dietary fat supplementation if additional energy is required.