The South Pasture Diet: Low Starch Feeding

by Jeanne van der Veen, M.S., P.A.S.

A Fad or Sound Advice

In the world of human nutrition, diet plans and recommendations can be found for just about any nutritional combination you can imagine. Some of the more recent trends in dieting involve eating a low carbohydrate diet. This same trend now appears to be occurring in the equine world as well. With increased awareness of carbohydrate related disorders in horses such as, but not limited to, laminitis, metabolic syndrome, Cushing’s, gastric ulcers, and Equine Polysaccharide Storage Myopathy, many equine nutritionists and veterinarians have been recommending a low carbohydrate or low starch diet for horses.

Understanding the equine digestive system can help to explain the basis for these recommendations. Horses are grazing animals. Their digestive tracts are designed for eating small amounts of forage throughout the day while moving or walking. Thus, the size and capacity of the equine stomach is very small and limited in its ability to digest large amounts of feed, particularly starch, at one time. In contrast, the hindgut of the horse consists of a large and highly developed cecum containing a vast microbial population for the fermentation of forage. This hind-gut fermentation system has allowed horses to thrive historically on low quality and often sparse forages without the need for grain or other supplementation.

Through the years, domestication of the horse and introduction of many breeds has led to horses being used for a variety of different activities and levels of performance resulting in changes to their nutritional requirements and in the way they are fed. Many horses today are often fed meals, particularly grain, once or twice a day and housed in stalls instead of roaming large fields or pastures. Although not natural to their digestive system, if managed correctly and balanced to their individual requirements, this method of feeding horses has worked with minimal complications. However, as more and more horses are treated as pets and living longer lives due to advanced medicine and improved diagnosis, the awareness of illnesses or disorders relating to the metabolism and feeding of carbohydrates has increased, leading to the question “What is the ‘carb’ content of my horse’s diet”?

Carbohydrates in the Equine Diet

When evaluating the carbohydrate levels in an equine diet, it is important to understand the role of carbohydrates and how the different carbohydrate fractions are used by the horse. Fiber components from hay, pasture, and other high-fiber ingredients such as soybean hulls, oat hulls, alfalfa meal, or beet pulp are classified as Structural Carbohydrates. Through fermentation in the hind-gut, these structural carbohydrates provide a natural source of fuel or energy to the horse for maintaining body condition, temperature, and all normal body functions. Fiber is also an important source of energy for long term, aerobic muscle function such as that used during endurance racing or eventing. Additionally, all horses require a minimal amount of forage or fiber ingredients (1.0 – 1.5 percent of body weight) for proper function of the digestive system.

Starches, sugars and fructans found in either grains (oats, corn, and barley), molasses or pasture and hay are classified as Non-Structural Carbohydrates (NSC). The non-structural carbohydrates also provide fuel or energy to the horse and can be economical sources of energy when individual requirements exceed the amount of energy provided by the fermentation of fiber. Starches and sugars can be hydrolyzed in the stomach and small intestine to provide readily available glucose for immediate energy need by the body or can be stored as glycogen or fat for future use. These versatile energy sources are also used for both aerobic and anaerobic muscle function and are the only source for short term anaerobic muscle function such as that used in flat-track racing. Any excess starch and sugars that escape digestion in the stomach and small intestine, along with any fructans, found in cool season grasses, will pass to the hindgut where they are rapidly fermented.

NSC and Carbohydrate Related Disorders

With hay and forage being high in structural carbohydrates and an important part of the equine diet, recommendations for feeding a low carbohydrate diet are technically not correct. It is the non–structural carbohydrates (starches, sugars, and fructans) and their metabolism in the horse that are currently being questioned and researched in relation to the numerous disorders associated with feeding high starch and sugar diets. Fortunately, not all horses are affected with or are at risk of developing a carbohydrate related disorder. For most horses, the NSC content of the diet is not a major concern. However, for horses that are at risk, such as those with a breed or genetic predisposition for starch related disorders, a history of laminitis or founder, equine metabolic syndrome, chronic tying-up, age-related disorders, or if feed management is a concern, evaluating the NSC content of the diet may be beneficial.

Although the causes and symptoms of the numerous carbohydrate related disorders are different, the current recommendations are very similar: Avoid rapid, large intakes of NSC and in some cases, as with some genetic anomalies involving glucose metabolism, eliminate as much NSC from the diet as possible. For horses at risk of or currently diagnosed with some of the carbohydrate related disorders, infrequent meal feeding of diets high in NSC, whether coming from grain, pasture or hay, can result in a drop in stomach ph as well as large fluctuations of plasma glucose and/or insulin leading to, or further aggravating such disorders. In addition, overloading the digestive capacity of the small equine stomach leads to the passage of starch and sugars to the hindgut where they are rapidly fermented. Rapid fermentation of starches, sugars, and fructans can lead to a series of events causing severe digestive upset and culminating in colic and laminitis or founder.

Evaluating NSC in Equine Diets

Several commercial laboratories offer analysis of starch and sugars contained in forages, grains or mixed feed. It is important to know what is actually being measured and reported when evaluating NSC, starch or sugar values so that correct comparisons can be made between products. When used appropriately, these analyses can be very helpful in selecting forages or feeds low in NSC. Values reported for NSC, starch or sugar should be used as guidelines only and not taken as exact figures. The laboratory methods and techniques for analyzing starch and sugar are not currently standardized and can vary significantly between labs. Variation also exits within the methods used due to difficulty in getting a complete and accurate analysis of the individual non-structural carbohydrate components.

Feeding a Low NSC Diet

Ensuring horses with carbohydrate related disorders receive a diet low in non-structural carbohydrates involves both feed management and selecting feeds that are low in NSC. With hay and pasture being the primary portion of most horses’ diets, managing for low NSC content is important. Forage NSC content varies based on many factors including species, plant part, season, time of day, and environmental conditions. Hay NSC varies based on when it was cut and conditions during drying. Some current recommendations for horses susceptible to carbohydrate related disorders involve denying access to pasture during the growing season, avoid grazing after cool nights followed by warm, sunny days, limit grazing to the early mornings and avoid afternoons when NSC may be highest, and avoid grazing stressed forages. Grazing muzzles should also be considered to limit access to forage while still allowing necessary exercise. Selecting hay that is more mature and lower quality may also be considered. Hay can also be rinsed with water and the water poured off to remove some of the sugars and fructans.

Feeding grain or commercial rations and other supplements involves starting with the horse’s individual requirements and selecting products that are formulated to meet those requirements. For horses with carbohydrate related disorders, selecting a product with a low NSC level may be necessary depending on feed intake. If additional calories are not needed, horses should only receive proper protein, mineral and vitamin supplementation and no grain. Careful feed management for feeding grain or commercial rations to horses and particularly those susceptible to carbohydrate related disorders involves feeding multiple meals, making feed changes very gradually, and preventing rapid intakes.

A Lifetime of Health and Performance

Horses should be fed as close to nature as possible, reflecting the design of their digestive system: continuous intake of small meals, high in fiber and low in NSC, throughout the day. Adjustments to the diet should be based on individual horse requirements, performance goals, health related concerns, and the feeding management situation. Diets should be properly balanced for all nutrients including water, protein, energy (fiber and NSC), minerals and vitamins. Horses should be maintained in good body condition and exercised regularly. Extremes in feeding and management should be avoided and common sense should be employed.

© Blue Seal Feeds – May, 2008