Equine Nutrition

Equine Nutrition
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 bone development and as most of this development occurs within the first year young horses need higher amounts than adults. Adults need calcium and phosphorous to maintain cell function and bone mineral. (arg.gov.sk.ca)
Micro-minerals or trace-minerals required by horses include Iodine, Copper, Zinc, manganese and selenium. Horses use Iodine for fetal development and to regulate metabolism. “inadequate iodine intake in pregnancy can cause serious fetal abnormalities. Foals may be born weak, may not suckle or stand. Thyroid glands can be enlarged (goiter) or normal. Rarely, foals are born hairless or may have ruptured extensor tendons and swollen joints. Iodine deficient newborns may be more prone to infections. Iodine deficient mares may or may not have goiter, a longer gestation and retained placentas. Iodine deficiency can be prevented by feeding iodized salt. Goiter is also a sign of too much iodine or iodine toxicity.” (arg.gov.sk.ca)
Copper has been promoted as a bone disease preventative as horses use copper in bone, cartilage, and pigment formation.
Lack of iron can cause anemia but is maor likely to “arise from blood loss due to internal parasites. Iron dextran used to treat baby pig anemia must not be given to horses since fatal, allergic reactions can occur.” (arg.gov.sk.ca)
“Conditions such as muscle pain or skin irritation were associated with low serum levels of selenium or zinc.” (Wichert et al.) “Deficiencies may cause hair loss and poor wound healing.” “Low intakes of selenium cause white muscle disease. Foals are born weak and may not be able to stand, suckle or breathe normally. Death is usually sudden. White muscle disease occurs mostly in foals but weanling and adult horses can be affected. Selenium deficient mares may have reduced fertility and an increased occurance of retained placentas.” (arg.gov.sk.ca) “Selenium was not recognized as an essential nutrient until the 1950s.” (Harris 1998)
Vitamins can be fat-soluble or water-soluble. Fat-soluble vitamins are A,D,E and K, they are stored in body fat and can be toxic if overfed. Those that are water-soluble are vitamins C and B-complex.
“Vitamin A is necessary for cell growth and maintenance. Carotene in forages is converted to vitamin A in the gut. In hays, carotene is destroyed by prolonged storage or overheating. Except for corn, most grains are low in carotene. Dietary vitamin A needs differ according to age.” (arg.gov.sk.ca)
“Vitamin A deficiency causes a rough hair coat, night blindness, increased susceptibility to infections, scally hooves, bone abnormalities, and reduced fertility. Deficiency must be severe to cause many of these signs. Too much vitamin A must be avoided. Toxicity occurs at 10-50 times normal intakes and causes weakened bone and skin lesions.” (arg.gov.sk.ca)
In weanling horses vitamin D deficiency will result in slowed growth, weak bone, and reduced appetite. Vitamin D is used for bone growth and is provide in the diet by sun-cured hays. (arg.gov.sk.ca)
White muscle disease is caused by deficiencies of vitamin E and selenium. Alfalfa hay, pasture and wheat germ oil are sources of vitamin E. (arg.gov.sk.ca)
Quality feeds meet the dietary requirements of vitamin K in horses, which allow normal clotting of blood. (arg.gov.sk.ca)
Vitamin C has not been proven necessary for horses. (arg.gov.sk.ca)
Vitamin B complex is given to horses for energy utilization, red blood cell formation, to improve performance and for normal skin and hoof growth. These are especially important for heavily worked horses. (arg.gov.sk.ca)
The necessary intake of water varies depending on physical and external conditions. “Water intake depends on size, the amount and type of diet fed, outdoor temperature, and the amount of work being done.” “Early pastures can have 80% water. Water intake by horses grazing these pastures can be low since much of the water needs are obtained from grass. Water intake increases by 20% in hot weather, 20-300% with hard work and 50-100% in lactating mares. About 50% of suckling foals may not drink water until they are weaned.” (arg.gov.sk.ca) Clean water should be constantly available in a safe manner for the horse. Any water system using electricity must be grounded as young horses like to paw at waterers. (arg.gov.sk.ca)
Native pasture has similar nutrient content to improved pasture, but a predisposition to being sparse makes the stocking rate of native pasture low. In improved summer pasture a mature horse requires four to five acres to forage, more on native pasture. Nutritional value is highest in spring and the nutritional value of immature plants is greater than that of mature plants. The nutrient levels differ between types of forage, as does waste, and palatability. Horses find alfalfa to be tasty and it is nutritious but it is also easily trampled so waste can be high. Red and white clover are also nutritious. Some forages should be avoided as they have harmful effects on horses. (arg.gov.sk.ca)
Grazing area management practices are mostly common sense. “These include: minimizing overgrazing; plants should not be grazed below 5 cm (2 inches). Regularly scattering or harrowing manure piles, removing injurious material such as wire, boards and toxic plants, mowing mature pastures to stimulate new plant growth, using safe fencing material (barbed wire fenses can cause serious injury), providing shade (trees or sheds), and providing water and supplement feed (if needed).” (arg.gov.sk.ca)
Hay is the main feed for horses. To choose a high quality hay look at type, leaf to stem ratio, stage of growth, presence of weeds mold or foreign matter, odor, color and have the feed analyzed. (arg.gov.sk.ca)
Alfalfa is high in energy. It is used in the diets of growing horses because of this and is the most common legume hay used for horses. It is prone to mold and has a habit of being dusty, but good curing reduces these problems. There have been claims that it damages kidneys but these claims have no basis. Alfalfa-grass mixture hays are less prone to mold and dustiness, and are more nutritious than straight grass hay. (arg.gov.sk.ca)
Grains are fed to horses because of their high starch, and therefore energy, content. Energy content varies in different varieties of grains but “is almost directly related to weight.” “All grains should be fed by weight and not volume. Grains vary greatly in quality and weight (see Table 8). Weight the grain. Know the weight of grain in the container you are using. One quart of oats contains 1/2 the energy content of a quart of corn. Substituting a coffee can of corn for oats doubles a horse’s energy intake.” (arg.gov.sk.ca) The digestive benefit of rolling or cracking oats is felt by foals and horses with poor teeth. Mature horses and those with good teeth get little if any benefit.
Corn and barley are grains that should be rolled or cracked. (arg.gov.sk.ca)
Protein supplements for horses include soybean meal, canola meal and skimmed milk powder. These are high quality and most often used. (arg.gov.sk.ca) (Harris 1998) states that in 1908 Anon reported Norwegian horses were fed soups containing boiled fish. Harris goes on to say that Icelandic ponies “may still be fed herring in the winter.” “However, the feeding of animal derived feed to a herbivore such as the horse is not a common (or recommended) practice.” Other feeds given to horses include wheat bran, for horses that are inside and unexercised; molasses, to reduce dustiness; and beet pulp, to fatten horses. (arg.gov.sk.ca)
Manufactured feeds have been available since the start of this century, but these were often expensive and of questionable quality. Pelleted feeds did not gain popularity until the 1960s. (Harris 1998) “Advantages of pelleted feeds are space economy, less dust, less waste and less selectivity by the horse.” “Disadvantages of pelleted feeds are higher total cost, the need for specific storage space and the inability to judge the quality of ingredients used to make the pellet.” (arg.gov.sk.ca)
Mineral supplements of calcium and phosphorus are often offered to horses with a carrier such as salt, rolled grain, of dried molasses to act as a bribe to get the horse to eat it. Vitamin supplements of A and D are added to equine diets. (arg.gov.sk.ca)
Feeding programs for horses are based on the animal’s age, weight, function, available feeds and management. (arg.gov.sk.ca)
The objective of the diet of an idle mature horse should be to maintain body tissue. This goal can be met by a diet of quality pasture or hay. The animal would probably also benefit from a calcium-phosphorus supplement. Water and salt should be constantly available. (arg.gov.sk.ca)
Growing horses need diets that are high in energy and nutrient to fuel their rapid growth. Weanling horses must be slowly started on high quality feeds. (arg.gov.sk.ca)
Yearling and two-year old horses can be summered on pasture, depending on the quality of the pasture grain may need to be supplemented. If in training two-year olds will need the extra energy that can be supplied by grain, but non-working two-year olds need less grain the yearlings. (arg.gov.sk.ca)
A working horse’s dietary needs vary greatly depending on the type and duration of work. Most of what the animal needs will be energy, but they will also need higher levels of minerals and protein. Care should be taken when increasing grain intake to prevent health complications. (arg.gov.sk.ca)
Pregnant and lactating mares have special needs. After the seventh month of pregnancy fetal tissues increase rapidly and the mare will need extra nutrients. Quality hay and dietary supplements are necessary. Fewer nutrient are needed in late lactation. (arg.gov.sk.ca)
Abnomal feeding behaviors horses are called vices. “Greedy-eating can be learned. Horses that must compete for feed early in life may adapt by gobbling their feed. Rapid eating can reduce digestive efficiency, cause colic from swallowed air or choke from poorly chewed feed. Adding large rocks to a manger forces the horse to slow down its eating speed.

Manure-eating is normal in foals less than 2 – 3 months of age. Foals get the needed bacteria and protozoa for their intestine by eating manure. Older horses may eat manure if their diets are low in fibre or protein, or if feed intake is limited. Manure-eating is undesirable because if promotes parasite infestation. Check the diet in all instances of manure-eating in adult horses.

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Wood-chewing horses gnaw away at boards with their teeth. They may or may not swallow the wood slivers. Softwood boards such as pine or spruce are easily ruined. Wood-chewing occurs mostly in bored, pellet-fed horses. Young horses develop this vice more quickly than older horses and wood-chewing occurs more in cold, wet weather. Aversion therpy by painting fences with creosote is largely ineffective. Lining boards with angle-iron is costly but effective.

Boredom is often the cause of wood-chewing. Adding long hay to an all pellet diet (0.5 kg/100 kg weight) or increasing exercise may reduce boredom and wood-chewing. Horses committed to wood-chewing are undetered by anything you do. In most cases, wood-chewing is not due to a nutritional deficiency but the nutrient content of the diet should always be checked to make sure it is adequate.” (arg.gov.sk.ca)
The facilities and amounts of feed needed for horses in different seasons depends upon the number of and location of the animals. Equipment for feeding indoors and outdoors differs. Outdoor horses must have shelter and water available to them. (arg.gov.sk.ca)
Nutritional disorders in horses include “Heaves which is a lung conditon similar to emphysema. It occurs in susceptible horses fed moldy hays or bedded on moldy straws. Pollen in pasture can also cause heaves. Good ventilation helps disperse mold spores but heaves can occur in outdoor-fed horses. Horses with heaves can be fed hays dampened with water, or fed pelleted or cubed hays.

Gas colics occur with sudden switches in diet; from low to high grainor from low to high quality hay. All feed changes should be made gradually.

Impaction colics occur in horses fed poor-quality feed (eg. straw, slough hay) especially is water is limited. Poorly digested feeds accumulate in the intestine and cause constipation. The dry mass that gathers distends the gut, causing local pain and colic. Water and good quality feed can reduce the occurance of impactions in horses.

Enteroxemia is mostly seen as foals but can occur in adults. This condition occurs when horses are switched suddenly from low to high quality feeds. Too much grain given to horses unaccustomed to grain, or a sudden switch from poor to high quality hays can cause this condition. Sudden death or colic occur.

Epiphysitis and contracted tendons are disorders of the musculoskeletal systems of young horses. Epiphysitis can occur at the fetlocks between 3 – 6 months of age and at the knees from 3 – 12 months to as late as 18 months. The area above the joint is irregular in shape and larger than normal. Usually several joints are involved. Most often the forelimbs are affected but hindlimbs can also be involved. The condition is seen in rapidly growing, muscular-bodied and ‘good-doing foals’. Quarter horses have a high incidene but other breeds with a similar body type are also affected e.g. Paints, Appaloosas and Thoroughbreds.

Epiphysitis is a bone reaction at the growth plate (zone of bone growth). The growth plate can be damaged by feeding imbalanced diets, feeding high energy diets free-choice or through abnormal conformation. High energy diets (often high grain diets) may cause changes in hormones that govern bone growth or may cause overly rapid weight and bone growth. A heavy body can increase strain on the growth plate especially with certain types of conformations such as upright pasterns and offset knees.

Regulating growth rate is the basis of prevention. Normal growth in foals is typified by a steady decline in average daily gains and skeletal growth from birth to one year of age. A balanced creep feed should be fed in regulated amounts to suckling foals by 2 months of age. Creep feeding promotes more uniform growth from birth to weaning. Grain intake of horses less than one year of age should be carefully contolled. Weanings of light horse breeding (mature weight 500-600 kg) should not be fed more than 3 kg (6 – 7 lbs) of grain or concentrate mix daily between 6 – 12 months of age in addition to good quality hays.” (arg.gov.sk.ca)
Poisonous Feeds:Additives that can be fatal and should be not be used or used with extreme caution are: