Horses are non-ruminant herbivores, who are naturally designed to move long distances on foot while foraging for food. In the wild, they spend about 16-18 hours a day searching for food and can cover distances of up to 20 kilometers. In contrast, domesticated horses typically walk an average of only 7.5 kilometers per day 1.
For horses, seeking roughage in the form of grazing is one of the most typical and essential behavioral needs of the species. Restricting these behavioral patterns can lead to stress, aggressiveness, and abnormal behaviors and other issues 2. Inadequate access to roughage has also been suggested to increase the incidence of sand ingestion 3,4. Horses do not typically consume plants that are harmful or dangerous to them if they can choose otherwise. Therefore, the opportunity for species-appropriate roughage consumption has a comprehensive impact on the overall well-being of the horse.
Studies have shown that high-energy, grain-based diets, combined with long feeding intervals, can impair the function of a horse’s digestive system. This, in turn, increases the risk of conditions such as gastric ulcers, colic, and laminitis. Starchy concentrates, especially when fed with a limited amount of roughage, have been particularly challenging for horses, according to research 5,6
Overview of the Horse’s Digestive System
The foregut of the horse consists of the esophagus, stomach, and small intestine. The hindgut is made up of the cecum, large colon, small colon, and rectum. The stomach serves as a storage area for food, and it is roughly divided in two parts. The upper part of the stomach has no mucous membrane or any glands that would produce gastric juices. The lower part on the other hand has glands, that produces gastric juices, that contains hydrochloric acid, pepsin, and gastric lipase.
In the stomach, feed gets prepared for digestion later in the digestive system. If the horse is fed too large meals, some of it will pass the stomach without sufficient chemical digestion, which will impair digestion later. On the other hand, it is important that there is always food in the stomach, because gastric juices are produced constantly. If the stomach is empty, the acid gastric juices can attack the stomach walls, causing gastric ulcers 7.
Dry matter and fiber
The horse’s digestive system requires a constant intake of fibrous roughage to function properly. This allows the stomach’s gastric fluids to maintain optimal acidity. Prolonged fasting, lasting over 2-4 hours, is unnatural for horses and can quickly lead to health issues. Fasting especially in the early morning hours can acidify the stomach quickly 8. Chewing generates saliva, which, when regularly produced, helps buffer the stomach acid produced continuously throughout the day. The longer a horse goes without chewing, the more acidic its stomach content becomes 9.
Horse’s diet should contain mostly forage. The unique digestive system enables horses to utilize most all the nutrients found in fibrous plant material.
The guidelines for feeding recommendations are given per kg dry matter (in Europe). This is important to note, because fresh feed always contains water, which doesn’t contain nutrients. Comparing hays and feeds only makes sense when you compare the nutrients per kg DM. It makes a difference if you feed a horse 10 kg of fresh hay or 10 kg of dry hay (which still contains water). For a healthy digestive tract and a healthy horse, the recommended amount of forage is 1,5 kg of dry matter/100 kg bodyweight. This means that the horse should be fed 1,8 kg of dry hay (83 % dry matter) / 100 kg bodyweight.
Fiber is an important part of the structure of the cell walls of plants, making sure they stay supported. Fiber is the most important part of the horse’s diet, giving horses up to 75 % of their energy. Fiber is digested via bacterial fermentation in the cecum and colon, turning it into volatile fatty acids (VFA). This fermentation in the hindgut of the horse is what allows horses to utilize the fiber portion as a nutritional energy source. The fatty acids can be absorbed and are used for energy. Additionally, fiber provides the horse with important vitamins like vitamin B1 and K.
Starch
The horse is a hindgut fermenter, which means, ingested fiber gets fermented in the large intestine. The digestion in the small intestine happens enzymatically, whereas microbes work in the large intestine. Starch for example should be digested in the small intestine, because the microbes in the hind gut struggle with the breaking down of starch. This leads to a drop in pH, which then again causes digestive issues for the horse. The feed travels quite fast through the small intestine though, giving it only a short time to be absorbed. Additionally, the enzyme amylase, that is responsible for breaking down starch, can’t be produced excessively 7.
So, if the feed portion contains a lot of starch, it can’t be broken down or digested in the small intestine. The current recommendation of starch is 1 gram / kg bodyweight / portion or 2 g/ kg bodyweight / day. In small portions, starch is a good source of energy for the horse. The fed amounts just must be moderate.
Conclusion Good quality roughage is the base of feeding horses. They are designed to have almost constant access to roughage. Limiting their roughage intake can have severe results for the digestive system and the horses’ overall health. Additionally, limiting roughage intake can cause stereotypic behaviors and aggression 10. If the horses need additional energy or other nutrients, feeding concentrates can be necessary. Choosing the right one is important, though. Too much starch especially can also cause problems in the gut. The main tips for feeding horses are giving them enough roughage and making sure they don’t have long fasting windows and keeping the starch content in the diet moderate.
References
(1) Hampson, B.; Morton, J.; Mills, P.; Trotter, M.; Lamb, D.; Pollitt, C. Monitoring Distances Travelled by Horses Using GPS Tracking Collars. Australian Veterinary Journal 2010, 88 (5), 176–181. https://doi.org/10.1111/j.1751-0813.2010.00564.x.
(2) Krueger, K.; Esch, L.; Farmer, K.; Marr, I. Basic Needs in Horses?—A Literature Review. Animals 2021, 11 (6), 1798. https://doi.org/10.3390/ani11061798.
(3) Husted, L.; Andersen, M. S.; Borggaard, O. K.; Houe, H.; Olsen, S. N. Risk Factors for Faecal Sand Excretion in Icelandic Horses. Equine Veterinary Journal 2010, 37 (4), 351–355. https://doi.org/10.2746/0425164054529373.
(4) Niinistö, K. E.; Määttä, M. A.; Ruohoniemi, M. O.; Paulaniemi, M.; Raekallio, M. R. Owner-Reported Clinical Signs and Management-Related Factors in Horses Radiographed for Intestinal Sand Accumulation. Journal of Equine Veterinary Science 2019, 80, 10–15. https://doi.org/10.1016/j.jevs.2019.05.012.
(5) Al Jassim, R. A. M.; Andrews, F. M. The Bacterial Community of the Horse Gastrointestinal Tract and Its Relation to Fermentative Acidosis, Laminitis, Colic, and Stomach Ulcers. The Veterinary clinics of North America. Equine practice 2009, 25 (2), 199–215. https://doi.org/10.1016/j.cveq.2009.04.005.
(6) Colombino, E.; Raspa, F.; Perotti, M.; Bergero, D.; Vervuert, I.; Valle, E.; Capucchio, M. T. Gut Health of Horses: Effects of High Fibre vs High Starch Diet on Histological and Morphometrical Parameters. BMC veterinary research 2022, 18 (1), 1–338. https://doi.org/10.1186/s12917-022-03433-y.
(7) Mishra, D. B.; Singh, P.; Bhalakiya, N.; Kumar, G.; Yadav, D. K. Chapter-10 Equine Digestive System. Emerging Trends in Applied Research 2021, 45, 133.
(8) Cipriano-Salazar, M.; Adegbeye, M. J.; Elghandour, M. M. M. Y.; Barbabosa-Pilego, A.; Mellado, M.; Hassan, A.; Salem, A. Z. M. The Dietary Components and Feeding Management as Options to Offset Digestive Disturbances in Horses. Journal of equine veterinary science 2019, 74, 103–110. https://doi.org/10.1016/j.jevs.2018.12.017.
(9) Luthersson, N.; Nielsen, K. H.; Harris, P.; Parkin, T. D. H. Risk Factors Associated with Equine Gastric Ulceration Syndrome (EGUS) in 201 Horses in Denmark. Equine Veterinary Journal 2009, 41 (7), 625–630. https://doi.org/10.2746/042516409×441929.
(10) Carvalho Seabra, J.; Hess, T.; Martinez do Vale, M.; Spercoski, K. M.; Brooks, R.; Dittrich, J. R. Effects of Different Hay Feeders, Availability of Roughage on Abnormal Behaviors and Cortisol Circadian Rhythm in Horses Kept in Dry Lots. Journal of Equine Veterinary Science 2023, 130, 104911. https://doi.org/10.1016/j.jevs.2023.104911.
