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Nutrition Part 1: Carbohydrates


The trend in equine nutrition is now moving away from sweet feeds and towards “low carb” rations. Dietary changes have been an important part of treating many equine diseases including Equine Cushing's Disease, Equine Metabolic Syndrome, Equine Polysaccharide Storage Myopathy, and others. To understand this feeding strategy, we need to know the science behind the buzz.


Horses are grazing herbivores, and their guts are designed to use fermentable fiber from forage for energy. Forage usually refers to grass or hay, and this type of feed is broken down by the microbes in the large intestine. Byproducts of this process are used by the horse. Forages contain mostly fiber. Technically, fiber is a specific type of carbohydrate called structural carbohydrate. However, forages also contain small amounts of substances familiar to us as carbohydrates. These are the sugars and starches, and they are more accurately called non-structural carbohydrates or NSCs. These NSCs are digested differently than the structural carbohydrates because they are digested in the small intestine through an enzymatic process, not bacterial fermentation. NSC digestion is a tricky thing for the horse for two reasons. First, the small intestine is easily overwhelmed and can handle only about 0.4% of body weight in feed. In addition, some starches are resistant to the digestive enzymes, so they pass into the large intestine. Here, starches are fermented by the microbes differently than their usual fiber meal. This can cause some serious gastrointestinal disturbances.


Keeping the NSC as low as possible is helpful for all horses, even those without the problems we listed above. It's useful to compare the NSC of some common feeds:


Feed

NSC

Alfalfa hay

11.3%

Grass Hay

13.8%

Oats

54.1%

Corn

73.3%

Beet pulp (without added molasses)

12.3%

Wheat bran

30.3%

(values from Equi-Analytical Lab, Ithaca, NY; NSC on dry-matter basis)


To make lower carb feeds, companies use less of high NSC ingredients like corn or oats, and rely heavily on other products such as beet pulp. It's important to remember that the calorie content of feeds is independent of the NSC. For example, beet pulp and oats are very similar in calories , but quite different with respect to NSC content.


We must consider the NSC in the forage as well as the grain we are feeding. NSC content of pasture and hay can be extremely variable. We used to assume that pasture was consistently low in NSC, but new research shows that it can be very high, especially under certain conditions. Drought, climate, time of day, weed content, and overgrazing (or anything else that stresses plants) can increase the NSC in forages. The only way to know the content of forages is through forage testing.


For horses that tend to be overweight, several low-calorie, low-NSC feeds are now available. For horses that need extra calories to gain or maintain weight, fat is added to the feeds. Fat is extremely calorie-dense and contains no NSC. Very high dietary fat has been shown to treat EPSM and other muscle disorders. You can read more about fat in Nutrition: Part 2 in our next newsletter.

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