Horses are “trickle feeders” (meaning they are designed to ingest relatively small amounts of food gradually over long periods each day) and “hindgut fermenters” (which means that the fibrous component of their diet is fermented in their large intestine). Their entire digestive system is designed to process fibrous plant matter almost constantly.
FIBRE AND DIGESTIVE SYSTEM IN HORSES
Horses left to their own devices in paddocks and in the wild spend about sixteen hours per day grazing and ingest a minimum of 1% of their own body weight in fibre (comprised mainly of pectin, cellulose, hemicellulose and lignin) each day. It translates to about 1.5 to 2.5% (or more in some cases) of their own weight per day in pasture and other fibrous plants.
Pasture and other fibrous plants provide other nutrients as well as fibre, eg protein, simple carbohydrates, starch, fat, vitamins and minerals.
Horses have small stomachs relative to their size but have large hindguts acting as a fermenting vat where the fibrous plant matter is digested and absorbed.
When a horse grazes or eats a feed most of the digestion of protein, carbohydrates (sugar and starch) fat and vitamins and minerals occurs in the small intestine, but all the fibre is fermented/digested in the large intestine.
WHY IS FIBRE SO IMPORTANT?
All mammals, including horses, are not able to digest fibre at all, and yet fibre is crucially important as a source of nutrition for horses. So how is it that fibre is such an important component of horses’ diets if they are unable to digest it?
The answer is that horses and all other mammals rely on billions upon billions of health-giving beneficial microflora (tiny single-celled micro-organisms) that live and breed in their hindgut to ferment the cellulose, hemicellulose and pectin which are components of fibre.
Only lignin (the component of fibre that makes some grasses and plants tough and stalky) is not able to be fermented by gut microflora. Therefore has no nutritional value, but it still has a role in toning the muscles surrounding the intestines and helping to bulk up the ingesta moving through and ‘sweeping out’ contaminants like sand from horses’ GI tracts.
Horse nutritionists teach that one of the best ways to prevent or treat sand in the gut in horses is to feed ad lib grass hay.
CONVERTING FERMENTABLE COMPONENTS IN THE FIBRE
The beneficial microflora in horses’ large intestines convert the digestible/fermentable components in the fibre to volatile fatty acids (some of which the ‘good bugs’ consume as a source of food) and the horse absorbs the rest of the VFAs through the hindgut lining where in turn they are converted to:
- glucose (the form of energy required by all organs and cells),
- glycogen (glucose stored in muscles),
- fat.
This is the reason why some feeds, although they are low in sugar and starch, are high in calories/energy; it is because they are very good sources of digestible fibre.
Beet pulp, for example, provides roughly the same calories as oats, but in the form of fermentable fibre (for slow release sustained energy), rather than sugar and starch from grain (which is useful as a source of quick release energy for horses in hard or fast work, but if fed to excess can cause blood sugar level fluctuations, insulin spikes and hindgut issues for horses).
FIBRE IS NOT JUST A FILLER
Many people think that fibre is just a ‘filler’ or is necessary to ‘bulk up’ a hard feed or keep a horse ‘busy’ while the horse is confined, but that it has little or no nutritional value.
However, nothing could be further from the truth. Fibre (except for the lignin component already mentioned) is highly nutritious and is a very valuable source of cool, slow release sustained energy for all horses, for maintenance, growth, reproduction and performance.
Feeds high in the fibre component known as pectin are considered particularly valuable and are known as Super Fibres because pectin is the most important component of fibre for boosting the numbers of beneficial gut microflora in horses’ large intestines and keeping the GI tract healthy.
Feeds high in pectin include beet pulp, lucerne hay, lupin hulls and soy hulls.
THE BENEFITS OF FIBRE IN HORSE'S DIET
As well as being a very valuable source of slow release energy in horses’ diets, fibre has other benefits for horses, including its ability to:
- Slow down the rate of movement of feed through the digestive tract allowing the nutrients to be digested and absorbed more efficiently.
- Act as food for beneficial gut microflora (fermentable fibre is prebiotic) so they can breed and proliferate, and this boosts digestive function and the absorption of nutrients as well as having beneficial effects on the immune system. By promoting beneficial microflora, a high fibre diet also discourages the overgrowth of pathogenic (disease causing) microflora that can lead to digestive disturbances including colic, inflamed intestinal lining, hindgut and associated behavioural issues, laminitis etc.
- Stimulate the production of more saliva than other lower fibre feed types and this helps buffer stomach acid and reduces the likelihood of ulcers. Horses produce stomach acid constantly whether they are eating or not, and ad lib access to pasture or other fibrous feed (eg hay, lupin hulls, beet pulp etc) is very helpful in buffering the stomach acid, and stimulates the production of saliva which contains sodium bicarbonate, which is a natural acid neutraliser.
- Provide calories/energy in a slow release sustained form that does not cause insulin spikes and blood sugar level fluctuations that can be caused by feeds high in sugar and starch (eg grain and grain by-products).
- Reduce the likelihood of stereotypical behaviours like crib-biting and windsucking that occur in horses who are stressed from being confined or from high energy/low fibre diets that do not simulate horses’ normal patterns of grazing on forage. In situations where horses don’t have 24/7 access to pasture, they should always be provided with ad lib hay to help prevent any digestive and behavioural issues.
- Encourage horses to drink more water (plus water can be added to feeds containing beet pulp, lupin or soy hulls etc) and this provides a reservoir of water and electrolytes in the hindgut which helps prevent dehydration and electrolyte depletion in horses during sustained bouts of exercise. This is particularly useful for horses involved in the sport of endurance.
Written by Elizabeth Funnell
Equine Nutrition Educator
Sub-editor Bryan Meggitt (BMedSc. PGCrtMedSc.)
Senior Scientist and Co-founder of CEN Horse Nutrition
References
Nutrient Requirements of Horses – sixth revised edition National Research Council
Super Fibres – Kentucky Equine Nutrition Equinews publication Jan, 2002
Fibre for performance horses: A Review – Journal of Equine Veterinary Science Richardson, K and Murray, J. A.M.D. 46, pp31-39