Shannon Pratt holds her Masters in Equine Nutrition from the University of Kentucky. She helped to develop the on-line Equine Nutrition course at the ERC, and is currently working on an equine nutrition workshop for the industry.

FIBRE FOR HORSES Shannon Pratt, BSc., MSc.

What is fibre? Fibre is the material of the plant cell wall that gives plants their rigidity. There are many types of fibre including lignin, cellulose, hemicellulose and pectin. These are all types of carbohydrate molecules made up of many glucose units bound by links that are indigestible by mammalian enzymes. However, microbial organisms located in the hindgut of the horse can break down these links and in doing so, create a useful energy source for the horse. These microbes can almost fully digest pectin and partially digest hemicellulose and cellulose, however they cannot digest lignin.

One can get an estimate of the amount of fibre in their horse’s diet through hay analysis and looking at feed tags. Fibre is described as crude fibre on feed tags which includes mostly the cellulose fraction and some lignin. On hay or grain analysis, the terms ADF or NDF will be used. NDF or Neutral Detergent Fibre is the component of the feed that is lignin, cellulose and hemicellulose. The ADF or Acid Detergent Fibre portion includes only cellulose and lignin. The higher the NDF/ADF values, the less digestible the feed is.

Simply because fibre is not easily digested by the horse does not mean that is shouldn’t be included in the diet. On the contrary, fibre is a very important component of the horse’s diet. This is due to the nature of the digestive tract of the horse. Over history horses’ digestive systems have adapted to support grazing for many hours of the day. Horses have an enlarged cecum and large intestine (large and small colon) which act as large fermentation vats for the microbial organisms living there. If fibre is not provided for these organisms they can die off and release toxins into the horse. Horses also have a strong desire to spend time foraging and chewing. This desire is easily satisfied through providing long stem forage sources. If this is not provided stable vices may develop.

Horses consume large amounts of fibre in the form of forages. When fibre is broken down by the microbial organisms they release volatile fatty acids, namely acetate, propionate and butyrate. Upon absorption acetate and butyrate can be used immediately by the horse for energy, or can be converted to fat for energy storage. Propionate can be converted to glucose or can also be converted to fat. Research has shown that for horses consuming high forage diets, these volatile fatty acids provide substantial amounts of energy for the horse. When the microbes ferment the fibre heat and gasses are also released as a by-product. This is a loss of useful energy to the horse and is an additional reason why simple carbohydrates, such as starches, provide more energy per unit weight than forages.

So how will this information affect what you feed your horse? Plants become more lignified when they grow. This means that older plants are less digestible to the horse. Young plants (first cut hays and well-maintained pastures) will have less lignin and therefore provide more useful nutrients to the horse. In addition, legumes such as alfalfa and clover tend to be more easily digestible than grasses such as timothy and orchardgrass. Alternatives to hay include hay cubes, haylages or straw. Straw is not a very good source of nutrients for the horse but it does satisfy the horse’s need to chew. Some feeds have higher levels of pectins than other fibre sources. For example, beet pulp is very high in fibre, but this fibre is mostly pectin. Therefore, beet pulp is an excellent source of fibre for the hindgut of the horse, but is also highly digestible. Other high fibre feeds include wheat and rice bran. These should be fed with caution however due to their high phosphorus and low calcium levels.

In summary, horses need good quality fibre sources for optimal health. Early cut long-stem hay or well-maintained pasture is the best source of highly digestible fibre for the horse. If this is not available, lesser quality hay, hay cubes, haylage or beet pulp may be fed to increase the fibre intake of your horse. Although lower in digestible energy than higher starch concentrates such as oats or corn, forage sources can provide all the energy (and even the protein, vitamins and minerals) required by a mature horse at maintenance. Horses that have higher energy or protein demands (due to heavy work, growth, pregnancy or lactation) will require more nutrients than what can be provided for by forages, and therefore concentrated sources of energy should be fed.