Nutrition Fundamental Series: Nonstructural Carbohydrates
Carbohydrates
Carbohydrates provide energy but the source of the carbohydrate and the type of digestion dictate the amount of energy that is ultimately available to the horse. The base unit of a carbohydrate is the monosaccharide (mono = one; saccharide = sugar) and how these basic units are connected to form different carbohydrates will determine the site of digestion and the nutritional value that is delivered.
What are nonstructural carbohydrates?
Carbohydrates can be divided into two general categories: nonstructural and structural carbohydrates. Starches and sugars are known as nonstructural carbohydrates and are digested by enzymes and absorbed in the foregut. Fiber, known as structural carbohydrates, is digested by microorganisms throughout the gut but primarily in the hindgut.
This fact sheet will discuss nonstructural carbohydrates including monosaccharaides, disaccharides and starch. Click here to learn about structural carbohydrates (fiber).
Facts about feeding nonstructural carbohydrates (starches and sugars) In general, a feedstuff that is high in fiber is low in nonstructural carbohydrates and low in energy. For example, grass hay is high fiber and low in nonstructural carbohydrates and energy. On the other hand, corn is low in fiber and high in nonstructural carbohydrates and energy. Integrity feeds are beet pulp/soy hull based formulas that are high in fiber and low in starch and do not contain the high starch grains corn and barley.
The starch in oats is more digestible by the horse than the starch in corn. Also, as starch content of a diet increases, meal size and frequency should decrease.
Nonstructural carbohydrates are simple sugars
The chemistry of nonstructural carbohydrates can appear complex but the basic unit is a simple sugar, aka monosaccharide (mono = one; saccharide = sugar). This simple carbohydrate exists in different forms and when linked together or connected in different combinations will form other types of saccharides including starches.
The most common monosaccharide is glucose, which is the sugar that circulates in the blood and is the primary source of energy for cells. Monosaccharaides alone are very low in plant foods that are consumed by the horse but are found in various quantities in fruits, berries, vegetables and honey. Their importance is how they’re linked together to form more complex saccharides in plants that provide a fuel source for the horse.
Nonstructural Carbohydrates – Monosaccharides
| Class | Simple forms of monosaccharides |
|---|---|
| Oligosaccharides | 6-carbon sugars:
|
5-carbon sugars:
|
Disaccharide – When two simple sugars (monosaccharides) are linked together they are called disaccharides (di = two; saccharide = sugar). For example, table-sugar and fruit sugar contain sucrose, the disaccharide that consists of glucose and fructose. Sucrose is also the sugar that exists in sugar beets and cane sugar. There is a small amount of sucrose in forages, but the disaccharide of nutritional importance for horses is the sugar in milk.
Milk-sugar or lactose is a disaccharide consisting of the monosaccharides glucose and galactose. Unlike other disaccharides, lactose has a unique benefit that promotes favorable bacteria and deters unfavorable bacteria in the foal’s developing gut. Forages contain little disaccharides. Molasses which is commercially prepared from sugar cane or sugar beets contains the disaccharide sucrose. Feeds with low levels of molasses (2 – 3%) will have substantially less sucrose than feeds like A&M (alfalfa & molasses), which may contain as much as 15% molasses. The common disaccharides are listed in the table that follows.
Nonstructural Carbohydrates – Disaccharides
| Class | Example | Components |
|---|---|---|
| Disaccharides | Sucrose (table sugar) | Glucose & fructose |
| Lactose (milk sugar) | Glucose & galactose | |
| Maltose (malt sugar) | Glucose & glucose |
Oligosaccharide – When several (3 to 10) simple sugars are linked together they are called oligosaccharides (oligo = few; saccharide = sugar). These types of carbohydrates are found in horse feeds. Sugar beets contain high levels of the oligosaccharide raffinose. This carbohydrate is also found in shredded beet pulp but at a much lower level. Beet pulp is the byproduct derived from the sugar extraction of sugar beets and is the key ingredient in many Integrity horse feeds.
Nonstructural Carbohydrates – Oligosaccharides
| Class | Example | Monosaccharide Components |
|---|---|---|
| Oligosaccharides | Raffinose | Glucose, fructose & galactose |
| Fructooligosaccharide, mananoligosaccharide & inulin | Fructose units |
Starch – The polysaccharides, starch and cellulose, are the major source of carbohydrates in a horse’s diet. Starch is an abundant energy source in the leaf and stem of forages and from the grain seeds including corn, oats, milo, barley and wheat.
Corn, barley and oats are the “pastas” or starches of the horse world. Wheat bran and rice bran are intermediate in starch content while beet pulp and soy hulls are very low in starch content. Starch content of forages is low. Bermuda grass has higher levels compared to other grass forages. The sugar and starch content combined for cereal grain hays, such as oat hay, barley hay & 3-way hay would have the highest levels of sugar and starch for dry forages.
Common polysaccharides are listed below.
Nonstructural Carbohydrates – Polysaccharides
| Class | Example | Monosaccharide Components |
|---|---|---|
| Oligosaccharides | Starch
|
Glucose |
How much nonstructural carbohydrates do horses need?
While carbohydrates are one of the six major nutrient groups and a required nutrient, a specific quantity such as grams of nonstructural carbohydrates per day has not established. The nonstructural carbohydrates importance is as a fuel source but the amount will depend on the production and working level of the horse.
Estimated % Sugar and Starch Content of Selected Feedstuffs
| Feedstuff | % Sugar | % Starch |
|---|---|---|
| Oats | 4.5 | 44. |
| Corn | 4.0 | 70.0 |
| Barley | 6.0 | 54.0 |
| Rice Bran | 6.0 | 18.0 |
| Wheat Bran | 8.5 | 23.0 |
| Beet Pulp | 10.5 | 1.5 |
| Soy Hulls | 4.0 | 2.0 |
Many horse owners are requesting feeds without molasses. So how much sugar from molasses is in 4 lbs of a sweet feed?
Example: An 1100 lb Quarter horse is consuming 4 pounds per day of a popular sweet feed with 6% molasses and also 18 lbs of grass hay. The horse owner is concerned with feeding molasses because it contains sugar. How much sugar is the horse actually eating? Let’s check.
- 4 lbs feed X 6% molasses = 0.24 lb of molasses in the 4 lbs of feed
- 0.24 lb of molasses X 454 grams (1 lb) =
108.9 grams of molasses - 108.9 grams X 40% sugar in molasses = 43.6 grams of sugar
- 43.6 grams ÷ 28.4 grams (1 oz) = 1.5 oz of sugar from molasses in 4 lbs of this sweet feed
Answer: The horse is consuming 1½ oz of sugar each day from the 4 lbs of sweet feed. Do you think that 1½ oz of sugar will be an issue with an 1100 lb Quarter Horse?
Final Thought
Many horse owners have expressed concern with the nonstructural carbohydrates in horse feeds and the potential adverse effects on horses that may be insulin sensitive, insulin resistant, or Cushing. These concerns have perpetuated self or non-clinical diagnoses of these conditions and elicit dietary demands that are often not practical, not balanced or unhealthy.
Recommendations that have evolved through trial & error suggest that for safe-starch commercial feeds, nonstructural carbohydrates levels should be less than 10 to 15%.
Perhaps, most importantly, one must be sure that their horse has been clinically diagnosed for one of the metabolic diseases (not just suspicious!) before becoming over-venturous with dietary changes. If your horse is clinically diagnosed as insulin sensitive, insulin resistant or Cushing, then recommendations from an equine nutritionist should be encouraged.