The Super in Super Fibres

You may be familiar with ‘super fibre’ products, such as sugarbeet pulp, soyhulls and haylage, but what makes these products stand out as superior sources of digestible energy amongst their traditional forage counterparts, hay and chaff?

The short answer is they have been shown to be more digestible than hay, possess superior fermentation characteristics and, ultimately, are an excellent source of digestible energy. 


The more readily a feedstuff is digested over the total digestive tract, the greater potential it has to provide higher nutritional value to the horse. Here is a review of the research that has looked into the digestibility of these super fibres.


Haylage is bagged hay that is made from the same pasture grasses or legumes. Instead of being allowed to dry out completely, it is baled when the moisture content is still relatively high (about 45-50%) and the bales are wrapped in multiple layers of plastic to exclude all air from the bale and allow a mild fermentation process to take place.

Haylage is slightly different than silage, which undergoes a more complete fermentation process and has a higher moisture content. Haylage bales are produced and marketed specifically for horses in many countries and are very popular as a low dust forage option.

Digestibility studies of grass haylage conducted using ponies by Moore-Colyer and Longland (2000) showed dry matter (DM) digestibility across the total digestive tract was 1.5 times that of grass hay. Furthermore, in a study by Waldron et al. (2012), using Thoroughbred horses, Controlled Fermented Lucerne (lucerne haylage) was found to have a significantly greater total tract digestibility than lucerne chaff.

The higher digestibility of the haylage may partly be explained by the maturity of the plant at the time it was cut. Haylage crops tend to be cut earlier than crops used for hay, and the young, leafy swards will have higher nutritional value, lower cellulose content and lower dry matter content than hay, making it easier to digest.

Nevertheless, the higher digestibility may also be aided by the microbial fermentation during the ensiling process, making the cell wall fraction of the plant more susceptible to digestive processes; thus, making the cell contents more available for digestion.

Sugarbeet pulp and soyhulls

Moore-Colyer et al. (2002) also demonstrated the superior degradability (how easily it breaks down during digestion) of sugarbeet pulp and soyhulls, compared to hay cubes. Dry matter degradation over the total gastrointestinal tract of ponies was significantly greater for sugarbeet pulp (85% of dry matter degraded) and soyhulls (68% of dry matter degraded), compared to hay cubes (56% of dry matter degraded).

The highly degradable nature of sugarbeet pulp and soyhulls within the digestive tract is due to their high content of hemicellulose and soluble fibre (e.g. pectin) fraction, in combination with lower cellulose and lignin contents.

Interestingly, the total digestive tract digestibility of forage products, such as grass hay, lucerne hay and haylage products, is improved by the addition of sugarbeet pulp. Murray et al. (2008) showed digestibility of dry matter and organic matter was significantly increased when a portion of the hay or haylage was replaced by sugarbeet pulp. Thus, combining super fibres may yield even higher digestible energy content than when fed alone.

The meal size effect

The digestibility of super fibres can be adversely affected by meal size. Ragnarsson and Lindberg (2010) reported greater levels of digestible energy were attained when Icelandic horses were fed smaller meal sizes of grass haylage, compared to when fed larger quantities. This observation was most likely due to the smaller quantities being more highly digested by the horses.

Thus, feeding smaller, but more frequent meals of super fibres, rather than one or two large meals, using a mechanism to slow haylage consumption (e.g. a slow feeder net) and ensuring only premium quality products are fed will allow horses to obtain the most benefit from inclusion of this feedstuff in their diet.

The fermentation process

The hindgut of the horse (caecum and colon) is like a large fermentation vat. During the natural process of microbial fermentation, the hindgut produces volatile fatty acids (VFAs), which the body uses as energy-yielding substrates (i.e. energy food). VFAs contribute significantly to energy metabolism and, of these, the greatest contributors are acetate and propionate.

The concentrations of the microbial organisms (the gut flora) and the VFAs they produce are greatly influenced by the type of diet – either positively or negatively. Super fibres have been shown to enhance hindgut fermentation and VFA production in a positive way; ultimately, resulting in a greater concentration of energy-yielding substrates.

Using ponies, Moore-Colyer et al. (2000) showed sugarbeet fibre produced significantly higher levels of total VFAs in the caecum, compared to hay cubes. Similarly, using Quarter Horses, Coverdale et al. (2004) fed an alfalfa lucerne/bromegrass hay diet with a portion replaced by 0, 25, 50 or 75% soyhulls (equating to 0kg, 2.2kg, 4.6kg and 5.6kg soyhulls per day).

Horses exhibited a significant increase in total VFA concentration in the caecum, which increased with increasing portion of soyhulls. Finally, Muller (2012) assessed levels of total VFAs in the faeces of 12 European Warmblood horses fed grass haylage cut at three different stages of maturity. The early cut haylage was found to produce significantly greater quantities of total faecal VFAs, particularly acetate and propionate, than the later cut haylages.

The enhanced production of VFAs in response to a diet containing haylage, sugarbeet pulp or soyhulls is facilitated by a high concentration of soluble fibres containing non-starch polysaccharides (NSP). Sugarbeet pulp and soyhulls contain high levels of pectins (particularly arabinose, galactose and uronic acids), which are highly fermentable. It is these characteristics that make these fibrous feeds potent sources of energy.

It should be highlighted the digestible energy potential of super fibres is also impacted by the health of the microbial population of the hindgut. If the microbial population has been adversely affected, for example by a previous poor diet or antibiotic treatment, it may take some time for the microbial population to re-balance itself in favour of digesting fibrous feed products.

Have we underestimated the digestible energy (DE) of these super fibres?

Whilst the formulas used to estimate digestible energy (DE) content are reasonably accurate for feed products, such as hay and most concentrate feeds, they may substantially underestimate the DE for feed products containing over 35% crude fibre (e.g. soyhulls) and for fibrous products with a high content of highly fermentable fibres (e.g. haylage, sugarbeet pulp and soyhulls).

According to Zeyner and Kienzle (2002), it is likely the DE values for sugarbeet pulp and soyhulls may be more comparable to that of oats and barley. Research examining the effects of all-forage diets in comparison to traditional high grain/low forage diets on performance horses certainly suggest this is may be the case.


  • Coverdale, J.A., Moore, J.A., Tyler, H.D. and Miller-Auwerda, P.A. (2004) Soybean hulls as an alternative feed for horses. Journal of Animal Science 82: pp.1663-1668.
  • Moore-Colyer, M.J.S., Hyslop, J.J., Longland, A.C. and Cuddeford, D. (2000) Intra-caecal fermentation parameters in ponies fed botanically diverse fibre-based diets. Animal Feed Science and Technology [online] 84(3-4): pp.183-197.
  • Moore-Colyer, M.J.S. and Longland, A.C. (2000) Intakes and in vivo apparent digestibilities of four types of conserved grass forage by ponies. Animal Science 71: pp.527-534.
  • Moore-Colyer, M.J.S., Hyslop, J.J., Longland, A.C. and Cuddeford, D. (2002) The mobile bag technique as a method for determining the degradation of four botanically diverse feedstuffs in the small intestine and total digestive tract of ponies. British Journal of Nutrition 88: pp.729-740.
  • Muller, C.E. (2012) Equine digestion of diets based on haylage harvested at different plant maturities. Animal Feed Science and Technology [online] 177: pp.65-74.
  • Murray, J.M.D., Longland, A., Hastie, P.M., Moore-Colyer, M. and Dunnett, C. (2008) The nutritive value of sugar beet pulp-substituted lucerne for equids. Animal Feed Science and Technology 140: pp.110-124.
  • Ragnarsson, S. and Lindberg, J. (2010a) Impact of feeding level on digestibility of a haylage-only diet in Icelandic horses. Journal of Animal Physiology and Animal Nutrition [online] 94(5): pp.623-627.
  • Richardson, K (2014) High energy fibrous feeds: Is there a place for them in performance horse diets? Master of Science Dissertation. Royal (Dick) School of Veterinary Science, University of Edinburgh.
  • Waldron, L.A., Thomas, D.G. and Pryor, I. (2012) Digestion characteristics of two forms of preserved lucerne forage fed to mature horses. Journal of Applied Animal Nutrition [online] 1(1): pp.1-4.
  • Zeyner, A. and Kienzle, E. (2002) A method to estimate digestible energy in horse feed. Journal of Nutrition 132: pp.1771S-1773S.
Karen Richardson, BSc (Hons), MSc Equine Science
Karen Richardson, BSc (Hons), MSc Equine Science

Karen Richardson graduated from the Royal (Dick) School of Veterinary Studies, University of Edinburgh, with a Master of Science in Equine Science (with Distinction). Now an independent equine nutrition consultant, Karen specialises in formulating diets for horses suffering nutrition-related disorders. Her research interest focuses on the use of high-energy fibrous feeds to reduce the incidence of nutrition-related disorders, maintaining performance and improving welfare for performance horses. 


Please enter your comment!
Please enter your name here

Recent Posts