Proper knowledge on the digestive system, especially its anatomy and physiology is essential for deciding on an appropriate diet that could satisfy the nutritional needs of animals. In case of sport horses, providing essential nutrition is key to improving or optimizing performances. Including all the needed nutrients in right proportions in their daily diet could ensure proper health and can avoid complications due to nutritional imbalances or deficiencies, which in turn could affect their performances. Horse being herbivorous in nature, the digestive system is equipped to a high fiber diet and they are used to longer periods of grazing. So their digestive system is prepared for dealing with small quantities of food at a time. But the digestive process appears to be rather prolonged. The anatomical structures and physiology of the digestive system is very much related to their feeding behavior and associated factors. The dietary needs of these animals also vary depending on their level of activity (Higgins & Martin, 2012). So there might be some variations in the nutritional requirements of sport horses in comparison to other horses as their expected health criteria and capabilities also differ.
Overview of the anatomy and physiology: There are two main sections in the digestive system of horses, the first part includes the stomach and small intestine that resembles the “monogastric digestive system of dog or man” and the second section is comprised mostly of the large intestine, which has some similarities to the “rumen of cow” (Luhr, n.d., p. 2) (fig 2). The digestion process starts in the mouth where the food gets lubricated by the saliva which is slightly alkaline and the food needs to be chewed properly in the mouth or else there is possibility for choking. The stomach of the horse is small and it is indicative of the fact that lesser quantities of food intake at a time would be appropriate. To aid digestion, hydrochloric acid is produced continuously in the stomach and so they need to eat little food in short intervals to avoid acidity problems. Regurgitation is not possible for horses and hence overeating could create lot of digestive problems (Williams, 2004). Small intestine is quite long and it forms about 21 meters in length and is divided in to three parts namely, duodenum, jejunum and ileum. “Enzymatic digestion” mostly occurs in the small intestine (Higgins & Martin, 2012, p. 71).
Pancreatic juice and bile aid the digestion process and the nutrients like fats, proteins and a major portion of carbohydrates are digested and assimilated here. Horses do not have gall bladder and hence make it difficult to digest fat. According to Williams (2004, p. 1) they can “digest up to 20 % of fat” but could “take up to 3 – 4 weeks to adjust”. Liver regulates the nutrient storage and absorption alongside with its detoxification functions. Large intestine is the longest organ and it contributes about 61 % of the digestive tract and has highly complex digestive functions (Cheeke & Dierenfeld, 2010). It contains lots of fermenting bacteria which assist in the digestion of fiber, cellulose and the carbohydrates.
Figure 1. Anatomy of the digestive system of horse with extended details of the large intestine (Source: Luhr, n.d., p. 2, 4).
Assessment on the physiology and anatomy of the digestive system revealed that there are lot of peculiarities associated with the digestive tract of horses, which needs to be considered for devising their nutritional mix. Providing nutrients in the right proportions at desired intervals is in fact needed for maintaining health, stamina as well as to enhance the sporting capabilities of the horses. Nutrition is an essential factor that can boost the performances of these sport horses. Ringmark et al (2012, p. 1) have pointed out the necessity for providing foodstuffs that can “support the natural behavior and digestive and metabolic systems of horses is therefore high, and the introduction of such diets will reduce welfare problems and health-care costs for the horse industry”. In agreement with these views, Halo et al (2009) has opined that nutrition plays a major role in improving the internal processes as well as in making them more efficient and capable. Each animal has specific nutritional needs and an understanding on the specific requirements of each of the major categories of nutrients in relation to their digestive system would be useful in identifying the right nutritional mix. Major categories of nutrients include proteins, carbohydrates, lipids or fats, vitamins, minerals and water and their role in sport horse diet is reviewed in the coming sections.
Water: In case of horses, water form a vital nutrient without which they will be able to survive for long and so provision for clean supply of water would be appropriate. Generally they require “about 2 quarts of water for every pound of hay they consume” and this could vary depending on the temperatures and their physical state (Williams, 2004, p. 1). Limiting water can affect performances and the quality of water is also of prime importance. Though the direct intake of water can be altered based on the moisture content of the diet, but it is estimated that consuming about 10 – 15 gallons of water per day would be appropriate for sport horses (Landefeld & Bettinger, 2013). Water has many important regulatory and digestive functions and so providing adequate quantities of water is crucial.
Proteins: Proteins contain amino acids and are “integral part of animal structure and metabolism” (Cheeke & Dierenfeld, 2010, p. 3). As proteins are essential for the development of muscles and so administering proteins or other protein supplements is essential to maintain vigor in sport horses. Dietary sources or supplements of proteins can be decided based on the digestibility of these food stuffs. Soybean, alfalfa, linseed, etc. are considered as effective sources of protein that can be included in their diet (Harris & Bishop, 2007). It is noted that about “8 to 10% proteins” need to be included in their daily diet of adult horses (Williams, 2004, p. 1).
Carbohydrates: These form the main source of energy and both soluble (starch and sugar) and insoluble (cellulose fibers) carbohydrates are essential for horses. The soluble carbohydrates are digested and assimilated in the small intestine, while the insoluble ones are digested by the fermentation of bacteria in the large intestine. The soluble forms occur in different foods like, corn, oats, barley, etc. (Cheeke & Dierenfeld, 2010). About 6 to 10 percent is present in all forages and the quantity can go even up to 30 % (Williams, 2004). High intake of carbohydrates at a time can cause digestive issues in horses. Compound feeds like “steam cooked, micronized or extruded maize and barley cereal grains” or supplements are given to horse to improve “starch availability and pre caecal digestion” (Harris & Bishop, 2007, p. 2).
Lipids: Fats or lipids are also essential nutrition for horses but in lower proportions because of the difficulty in digesting and absorbing fats. Feed mixes with fat content about 2 – 5 percent is found to be appropriate for horses than the ones with greater fat content (Harris & Bishop, 2007). Though fats are good sources of energy the digestibility factor in fact restricts the quantity of lipid intake. Crandell (2010, p. 136) consider fat in low quantities as an “excellent addition to any well-balanced diet for the endurance horse”. Supplementing small quantities of vegetable oils is advisable.
Vitamins: Both fat soluble and water soluble vitamins are required during the different growth stages of sport horses. As vitamins are present in the green forage there is not much need for providing vitamin supplements in the diet if the horses are fed with good quality green forage. Williams (2004, p. 1) has opined that “horses that are under heavy exercise or under increased levels of stress also may benefit from vitamin E supplementation”.
Minerals: Minerals like calcium, potassium, sodium, phosphorus, chloride and sulphur form essential macro minerals that are required in small quantities but have specific and critical functions. “Calcium and phosphorus are well recognized for their acting on the bones; sodium, potassium and chloride play a role of electrolytes” (Galik et al, 2012, p. 113). According to Williams (2004, p. 1) “calcium and phosphorus are needed in a specific ratio ideally 2:1, but never less than 1:1”. Right percentages of macronutrients should be included in the diet of horses. Micronutrients like magnesium, zinc etc. can be included in very small proportions in the diet.
|1.||Water||10 – 20 gallons per day
|2.||Proteins||10 – 15 % by weight per day
|3.||Carbohydrates (both soluble and insoluble)||40 – 50 % by weight per day|
|4.||Fats||2 – 5 % by weight per day
|5.||Vitamins||Vit A 20300 IU / kg; Vit D 3000 IU / kg;
Vit E 363 IU / kg; Vit B1 25.4 IU / kg
|6.||Minerals||Chlorine 20g / kg; Sodium 12g / kg; Calcium 10g / kg; Phosphorus and Magnesium about 5g / kg|
Table 1. Daily dietary nutrient requirements of the sport horses (Adapted from: The Merck Veterinary Manual, n.d, p. 1)
It is seen that sport horses have peculiar digestive system and the proportion of the nutrients and their feeding habits are very much linked to it. As the health and fitness of the animal is directly related to their performances it is essential to provide a diet that is nutritional and balanced. At the same time, the diet might include all the essentials in correct proportions in order to avoid metabolic problems or imbalances. Bergero and Valle (2007) has opined that the quality and quantity of the feed stuff need to be assessed in relation to the specific requirements of the horse prior to administering a diet. It is difficult to decide on a perfect nutritional diet for the sport horses as lot of parameters can “influence the success of a feeding plan such as owner expectations, metabolic and digestive differences among horses, physical activity and stable conditions” (Bergero & Valle, 2007, p. 639). Performances of the sport horses can be made optimal only through satisfying their nutritional requirements effectively. Decisions on the sources and supplements of the nutrients are also crucial as digestibility factor strongly influences the assimilation and conversion processes. Latest researches indicates that “alternative fiber sources” and other nutritive supplements could suffice the conventional feed and forage as the possibility for causing digestive imbalances are minimal (Harris & Bishop, 2007, p. 7). Processing of the food stuffs it could alter the digestibility factor and such activities could be useful in developing a more controlled and effective diet.
Based on the assessments on the nutritional requirements of sport horses, it was seen that a highly balanced diet that can suffice their health requirements could influence their performances as well. The digestibility factor of the feed or supplements or additives needs to be considered prior to deciding on the diet of sport horses. Digestive imbalances could affect their health and even their performances. Special care need to be taken for deciding on the dietary mix and feeding intervals in accordance with the limits of the peculiar digestive system of sport horses. Strong relation between health and performances of animals in fact make it all the more important for identifying highly digestible and nutritional diet for the animal, which is highly subjective. In order to optimally utilize their potential the dietary essentials has to be supplemented in the right proportions and at desirable times.
Bergero, D. & Valle, E. (2007). A multi-factorial approach to the nutritional requirements of sports horses: critical analysis and some practical applications. Ital.J.Anim.Sci., 6 (suppl. 1): 639-641.
Cheeke, P. R. & Dierenfeld, E. S. (2010). Comparative animal nutrition and metabolism. Cambridge University Press, UK.
Crandell, K. (2010). Observations and recommendations for feeding the endurance horse. Proceedings of the 2010 Kentucky Equine Research Nutrition Conference, April 26 – 27, Lexington, KY.
Gálik, B., Bíro, D., Halo, M., Juráček, M., Šimko, M., Massányi, P. & Rolinec, M. (2012). The effect of different macro mineral intakes on mineral metabolism of sport horses. ACTA VET. BR NO, 81: 113–117.
Halo, M., Hollý, A., Mlyneková, E., Polyaková, I., Horný, M. & Kovalčík, E. (2009). Influence feeding and training on the metabolic profil sport horses. Journal Central European Agriculture, 10 (4): 411 – 416.
Harris, P. A. & Bishop, R. E. M. (2007). Recent Developments in Equine Nutrition and Feeding. Journal of the Royal Agricultural Society of England, 168.
Higgins, J. & Martin, S. (2012). Horse Anatomy for Performance. UK: David and Charles.
Landefeld, M. & Bettinger, J. (2013). Water effects on livestock performance. The Ohio State University Extension, The Ohio State University. Retrieved March 15, 2013, from http://ohioline.osu.edu/anr-fact/0013.html
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Ringmark, S., Roepstorff, L., EssénGustavsson, B., Revold, T., Lindholm, A., Hedenström, U. & Jansson, A. (2012). Growth, training response and health in Standardbred yearlings fed a forage only diet. Animal, null, 18. Retrieved March 14, 2013, from http://www.slu.se/PageFiles/76043/YearlingsPublicerad.pdf
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Williams, C. A. (2004). The basics of equine nutrition. RUTGERS, New Jersey Experiment Station, Equine Science Centre, FS 038. Retrieved March 15, 2013, from http://www.esc.rutgers.edu/publications/factsheets_nutrition/FS038.htm