Carbohydrates

Carbohydrates Overview:

• Main source of energy for a horse

• Needed for horses to metabolize fats

• Formed in plants as a result of photosynthesis

• Make up about 75% dry matter in plants

• Carbohydrates are the collective term for: Sugars, Starches, Fibre

Food Triangle: Forage (CHO content):

• CHO's make up the majority of nutrients in any plant-based meal

• In general, lower percentages in hays, higher in corn and oats

• Grass-based hays have more CHO's than hay with legumes

• Example values: Alfalfa hay — soluble carbohydrates 53%; Yellow corn — soluble carbohydrates 82%; Whole oats — soluble carbohydrates 70%

Carbohydrate Forms:

• Structural (Fibres): Found in hay or pasture plants; often referred to as fibre, found in the cell wall of the plant; may also be called "neutral detergent fibres" or "crude fibre" on a lab analysis; beet pulp, soybean seeds, and old pasture grass are good examples

• Simple (Sugars & Starches): Normally found in grains; non-structural CHOs (NSC), associated with the inner portion of the plant cell or cell contents

How CHO's Form:

1. Leaves take in CO2 from the atmosphere, water from soil, and light from the sun to create energy that keeps the plant alive

2. Glucose is created

3. When glucose is created in the leaves, it's converted to sucrose and moved to the plant's vascular system at the lower base of the plant, for later use when the plant needs to grow

4. When growth starts, sucrose provides the energy for new plant tissue, converting it into complex CHOs such as cellulose, pectin, and lignin to make up the walls/structure of the plant

• This is how a plant can survive stress

• Experienced hay growers know not to cut the grass too short or the NSC will be depleted, making it harder to initiate regrowth

Digesting and Absorbing CHO's:

1. Mostly digested and absorbed in the small intestine as glucose

2. CHOs (simple sugars) get digested in the foregut (SI), then glucose and other simple sugars are absorbed into the bloodstream

3. Blood carries them to cells to use as a primary energy source

4. If not fully digested, they get fermented by microorganisms in the large intestine (most often complex CHOs)

5. The byproduct of microbial fibre digestion is volatile fatty acids (VFAs), which can then be used by the horse as energy

6. VFA's can be used to make fat for storage, glucose for immediate energy, or used as an energy source for the cells in the GI tract

Too Many Simple CHO's:

• Insulin resistance (Equine Metabolic Syndrome)

  • Insulin is produced by the pancreas in response to hyperglycemia

  • Insulin helps metabolize sugar by encouraging glucose uptake from blood into tissues

  • High blood glucose = high insulin = insulin resistance

• Obesity

• Laminitis

• Too much non-digestible fructose = lactic acid production = toxicity and vasoconstriction

Advice:

• Avoid fresh grasses

• Soak hay for 16 hours at mid-temps

• Exercise to maintain blood flow

• Keep NSC to roughly 10% in dry matter

Too Many VFA's:

• Volatile Fatty Acids provide 30-70% of the horse's energy needs (Mad Barn, 2023)

• Too much VFA production will increase lactic acid, reducing the pH in the hindgut

• This can lead to major health issues such as hindgut acidosis, colic, and laminitis

• A decrease in pH in the hindgut will create a disturbance to the microbial population, causing inflammation of the GI tract and making it less resistant to pathogens/toxins, less effective at digesting feed, and subsequent immune problems

• Decreased pH increases risk of GI ulcers

Structural CHO's (Fibre):

• Cellulose is the most common type and is made up of glucose molecules; the bonds holding them together is what makes it strong

• It relies entirely on microbes in the hindgut to break it down — slow-release energy

• Fun Fact: Humans can't access fibre for energy (Dengie, 2007)

• If there's a lack of fibre-digesting microbes in the hindgut, horses won't be able to use this fibre as an energy source