The digestive system of the horse consists of a simple stomach, small intestines, cecum, large and small colons, rectum and anus. The horse's stomach is comparatively small for its size. The stomach of an average horse has a holding capacity of about two gallons. This may be the reason horses eat small but frequent meals. From the stomach food moves to the small intestine, which is the main site of digestion. The small intestine empties into the cecum. The cecum; along with the large colon; make up the large intestine. Digestion in the large intestine occurs by action of bacteria and protozoa. (arg.gov.sk.ca) The energy content found in feeds and how it is measured in Kilocalories (kcal). (arg.gov.sk.ca) which is also the measure used for calories in human consumption. Equine energy intake is measured in megacalories (Mcal) which are equal to 1000 calories. (arg.gov.sk.ca) The total energy in feed is called gross energy. The amount of the feed's gross energy that is used by the horse is called Digestible Energy or DE. Total Digestible Nutrients (TDN) is also a measure of feed content energy, it is reported in percentages and converts between calories and weight. (arg.gov.sk.ca) Carbohydrates supply 80-90% of dietary energy. Sugars, starch, cellulose and related substances are carbohydrates. Starch is more easily digested than cellulose. Grains are easy to digest as they are 60-80% starch. (arg.gov.sk.ca) A recent study conducted by Sharon R. Bullimore et. all. investigated the result of supplementing the diet of endurance horses with fructose rather than glucose. They "conclude that fructose is well-absorbed by horses and rapidly converted to glucose." An assessment of adequate energy intake can be established by evaluating body condition. Deficient diets result in weight loss in the horse. Alternate causes of weight loss are internal parasites and disease. Excess energy intake wall cause obisity which stresses joints and reduces athletic ability. (arg.gov.sk.ca) A horse in moderate physical condition is described as "Back level. Ribs cannot be visually distinguished but can be easily felt. Fat around tailhead beginning to feel spongy. Withers appear rounded over spinous processes. Shoulders and neck blend smoothly into body." (Henneke et al., 1981) Protein is necessary in a horse's diet as they can not produce the amino acid lysine and must be supply it in their feed. The horse's protein requirements vary depending on age and function. Young horses needing more as they are still developing tissues made of protein. Mares in late pregnancy and those suckling a foal also need increased amount of protein. A horse given too much protein will break it down to glucose or fat. The health related results of too little protein are weight lose and young horses could have skeletal stunting. (arg.gov.sk.ca) The energy of fats is 2.5 that of carbohydrates, the percentage of fat in a typical diet is 5%. Most diets provide enough fats, which contain fatty acids for healthy skin. (arg.gov.sk.ca) Macro-minerals and micro-minerals (trace minerals), refers to the amount of mineral in the diet. Trace minerals are essential. "At the start of this century," "very little was known about the importance of even the macro-minerals; the role of trace elements had not been established and the work on vitamins was about to start." (Harris 1998) Needed macro-minerals are potassium, magnesium, sodium, chloride, calcium and phosphorus. Most forages contain enough potassium to meet a horse's requirements. Magnesium requirements in horses are usually fulfilled by hays. "Deficiency is not likely with typical diets but might occur on high grain diets or on early spring pastures. Magnesium deficiency causes staggering, nervousness, and convulsions. This is uncommon in horses." (arg.gov.sk.ca) Sodium and chloride were once viewed as unimporatant (Harris 1998) but are now seen as necessary for horses. Calcium and Phosphorus are needed for...
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