Nutrition

Nutrition


Carbohydrates



Basic Information image



Overview and Goal(s)




• The horse is anatomically designed as a grazing, hind-gut fermenting herbivore, with a range of carbohydrates—hydrolyzable to fermentable—as its primary energy source.


image Pastures and hay contain fermentable carbohydrates that provide constant energy and maintain the integrity of the microbial population in the equine hindgut.

image Grain concentrates contain hydrolyzable carbohydrates that provide efficient fuel for performance.

Carbohydrate Digestion and End Products



• Carbohydrates may be hydrolyzed or fermented in horses, depending on the chemical linkage of their molecules.


image Hydrolyzable carbohydrates include simple sugars (eg, glucose, fructose), disaccharides (eg, sucrose, maltose, lactose), and starch. Starch consists of long chains of glucose.

image Small intestinal enzymes hydrolyze starch and disaccharides into simple sugars.

image Absorbed simple sugars fuel equine performance, especially prolonged or high-intensity exercise, through efficient production of ATP in the Krebs cycle, and replenishment of muscle glycogen.

• Fermentable carbohydrates resistant to digestion by mammalian enzymes include the following:


image Soluble fibers (eg, gums, mucilages, pectins)

image Fructans and galactans (medium-chain sugars containing fructose or galactose)

image Starches resistant to enzymatic hydrolysis (encased in a seed coat or due to chemical structure)

image Insoluble fibers, hemicellulose, cellulose, and lignocellulose

• Horses rely on microbial fermentation in the hindgut to break down structural carbohydrates. Fermentation produces mainly volatile fatty acids (acetate, propionate, butyrate, and, to a lesser extent, lactate), gas, heat, and B-complex vitamins. Absorption of volatile fatty acids is integral to maintaining colon pH above 6, as required for optimal populations of microbes.


• Proportions of volatile fatty acids produced are dependent on substrates. Slow fermentation is desired:


image Forage diets high in fiber favor slow fermentation and production of acetate and butyrate.

image Increasing grain over forage favors rapid fermentation, decreases efficiency of fiber utilization, and alters the microbial ecosystem.

image “Grain overload” or “starch overload” occurs when excessive starch intake overloads the capacity of small intestinal hydrolysis and passes into the hindgut. When starch exceeds 4 g per 100 kg body weight per meal (approximately 5 lb of a traditional grain concentrate), it is rapidly fermented in the hindgut.

image Fructans pass through the small intestine and are rapidly fermented in the hindgut.

image Rapid fermentation favors proliferation of Lactobacilli spp. and production of lactate, which is poorly absorbed and may cause osmotic diarrhea, colic, and increased risk of laminitis and founder.

Carbohydrates in Horse Forages and Feeds



• Forages: During photosynthesis, green plants produce simple sugars. When sugar production exceeds the energy requirements of the plant, sugars are converted to storage carbohydrates, either starch or fructans.


image Cool season pasture grasses accumulate fructans. Legumes and warm season grasses accumulate starch.

image Fructan and starch concentrations in pastures fluctuate with season and diurnally from night to day or shade to sunlight.

image Fructan and starch concentrations generally rise during the morning, peak in the afternoon, and decline to a low overnight.
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Nutrition

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