When it comes to managing the carbohydrates in a horse's diet, knowing the basics of how horses digest food is half the battle. Laurie Lawrence, PhD, an equine nutritionist from the University of Kentucky's Department of Animal and Food Science who gave a presentation at the University of Kentucky's Breeders' Short Course, held Jan. 22 in Lexington, confirmed that managing a horse's carbohydrate intake is easiest with an understanding how the digestive tract functions and how different types of feed contribute to equine nutrition.
"The main dietary goals related to carbohydrates are to provide the horse with adequate digestible energy (or adequate calories), to keep their GI (gastrointestinal) tract healthy, and to provide adequate energy stores (or enough energy to perform their required actions)," Lawrence said. In doing so, it's important to consider each horse's energy requirements before feeding. A lean Thoroughbred in consistent training, for example, will have a much higher energy requirement than a pasture pony.
Veterinarians and nutritionists often suggest low fat, low starch, high fiber diets for overweight horses and ponies as a way to help them slim down. These diets also are commonly recommended for horses at risk for diseases such as equine metabolic syndrome and laminitis (founder), as most horses at high risk for these conditions are overweight. For these horses, a high-fiber diet is thought to be beneficial for keeping them healthy.
During her presentation Lawrence explained that an understanding of how the digestive tract functions makes it much easier for an owner to develop an individualized feeding program for each horse.
"There are two main parts of the digestive tract: the foregut and the hindgut," Lawrence said, adding that the foregut houses the stomach and the small intestine, and the hindgut is home to the large intestine. She also pointed out that there are many different types of carbohydrates in the horse's diet, and that different types are digested and metabolized differently.
Lawrence said that minimal carbohydrate digestion actually takes place in the stomach; most of the digestion takes place in the small and large intestines. The small intestine primarily digests the sugars and starches in a horse's diet, while the large intestine digests the fiber.
She explained that horses digest sugars and starches (which are specific types of carbohydrates) primarily in the small intestine. These substances are found in most types of grain-based concentrated feed (such as pellets and sweet feed) and in forage. Both sugar and starch are absorbed into the body as glucose.
Fiber, on the other hand, is digested by microbes in the large intestine, Lawrence said. The term "fiber" refers to carbohydrates that can't be digested by the horse's own enzymes. There are many different kinds of fiber including cellulose, hemicellulose, pectin, and fructan. Cellulose and hemicellulose generally come from pastures, pectin from beet pulp and alfalfa, and fructan generally comes from cool season grasses like Bluegrass or Timothy.
Sugars and Starches and Fibers, Oh My!
According to Lawrence, carbohydrates play an important role in the horse's diet. So while cutting back on certain carbohydrates might be ideal for some horses, eliminating them from the diet is both inadvisable and almost impossible to achieve.
Sugars and starches are absorbed into the body as glucose. Despite the fact that glucose can be converted to fat and stored on the horse's body, it plays several important roles in the body. Glucose is essential to brain function in horses and also aids in storing energy in the muscles.
Both of these substances are energy sources for the horse. Because they are digested rapidly by the small intestine, the energy is released quite rapidly into the body. This will give the horse a short burst of energy rather than sustained energy.
Fibers, on the other hand, are digested slowly. They provide the horse with sustained energy that can be used over longer periods of time. Fiber digested by the microbes in the large intestine yields volatile fatty acids, which also are used by the horse as an energy source. Lawrence also pointed out that some types of fibers are digested more rapidly than others. Fructan, for example, can be digested rapidly by the microbial population that lives in the horse's hindgut. Excessive consumption of grass pasture that is high in fructan might cause problems in horses, especially those that are predisposed to laminitis.
Lawrence stressed that both fats and oils are additional good calorie sources for horses. She added that they are not carbohydrates, nor can they form carbohydrates. In addition she noted that fats are very high in calories compared to fiber or even starch. If you are trying to get your horse to slim down, she said, a high-fat diet is not a good choice.
Putting it All Together
So what does this mean when it comes to developing a feeding plan? According to Lawrence, consider each horse's work load, body type, and nutritional needs before feeding.
A horse that is doing little to no work might maintain a good body condition and receive adequate energy from a diet of forage and a small amount of balancer pellets (which will provide the vitamins and minerals the horse needs). A horse that works consistently or has a slightly harder time maintaining weight will likely need both forage and concentrate to maintain his required energy level. And a horse in heavy work might need a fat or oil supplement in addition to both forage and concentrate to maintain his required energy level.
Lawrence suggests consulting an equine nutritionist for more information on how to properly manage the carbohydrates in your horse's diet.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.