Equine nutrition

Horses and other members of the genus Equus are adapted by evolutionary biology to eating small amounts of the same kind of food all day long. In the wild, horses ate prairie grasses in semi-arid regions and traveled significant distances each day in order to obtain adequate nutrition. Therefore, their digestive system was made to work best with a small but steady flow of food that does not change much from day to day. Chewing and swallowing Digestion begins in the mouth. First, the animal selects pieces of forage and picks up finer foods, such as grain, with sensitive, prehensile, lips. The front teeth of the horse, called incisors, nip off forage, and food is ground up for swallowing by the premolars and molars. Bile from the liver acts here, combined with enzymes from the pancreas and small intestine itself. Equids do not have a gall bladder, so bile flows constantly, an adaptation to a slow but steady supply of food, and another reason for providing fodder to horses in several small feedings. The microbes in the cecum produce vitamin K, B-complex vitamins, proteins, and fatty acids. The reason horses must have their diets changed slowly is so the microbes in the cecum are able to modify and adapt to the different chemical structure of new feedstuffs. The large colon, small colon, and rectum make up the remainder of the large intestine. The large colon is long and holds up to of semi-liquid matter. Its main purpose is to absorb carbohydrates which were broken down from cellulose in the cecum. Due to its many twists and turns, it is a common place for a type of horse colic called an impaction. The small colon is also long, holds about , is the area where the majority of water is absorbed, and where fecal balls are formed. The rectum is about one foot long, and acts as a holding chamber for waste, which is then expelled from the body via the anus. ==Nutrients==

Like all animals, equines require five main classes of nutrients to survive: water, energy (primarily in the form of fats and carbohydrates), proteins, vitamins, and minerals. Water Water makes up between 62-68% of a horse's body weight and is essential for life. Horses can only live a few days without water, In the winter, snow is not a sufficient source of water for horses. Though they need a great deal of water, horses spend very little time drinking; usually 1–8 minutes a day, spread out in 2-8 episodes. Water plays an important part in digestion. The forages and grains horses eat are mixed with saliva in the mouth to make a moist bolus that can be easily swallowed. Therefore, horses produce up to or 85 lb. of saliva per day. Horses that are heavily exercised, growing, pregnant or lactating need increased energy and protein in their diet. as well as gain excessive weight. Fat exists in low levels in plants and can be added to increase the energy density of the diet. Fat has per kilogram of energy, Because equids have no gall bladder to store bile, it flows continuously from the liver directly into the small intestine. Fat, though a necessary nutrient, is difficult for them to digest and utilize in large quantities. However, they are able to digest a greater amount of fat than can cattle. then barley and oats. Forages normally have only 6-8% soluble carbohydrate, but under certain conditions can have up to 30%. Sudden ingestion of large amounts of starch or high sugar feeds can cause at the least an indigestion colic, and at the worst potentially fatal colitis and/or laminitis. The main building blocks of protein are amino acids. Alfalfa and other legumes in hay are good sources of protein that can be easily added to the diet. Most adult horses only require 8-10% protein in their diet; however, higher protein is important for lactating mares and young growing foals. Some pastures are deficient in certain trace minerals, including selenium, zinc, and copper, and in such situations, health problems, including deficiency diseases, may occur if horses' trace mineral intake is not properly supplemented. Calcium and phosphorus are needed in a specific ratio of between 1:1 and 2:1. Adult horses can tolerate up to a 5:1 ratio, foals no more than 3:1. A total ration with a higher ratio of phosphorus than calcium is to be avoided. Foals and young growing horses through their first three to four years have special nutritional needs and require feeds that are balanced with a proper calcium:phosphorus ratio and other trace minerals. A number of skeletal problems may occur in young animals with an unbalanced diet. Hard work increases the need for minerals; sweating depletes sodium, potassium, and chloride from the horse's system. Therefore, supplementation with electrolytes may be required for horses in intense training, especially in hot weather. ==Types of feed==

, make up the largest portion of the equine diet by weight. Equids can consume approximately 2–2.5% of their body weight in dry feed each day. Therefore, a adult horse could eat up to of food. Foals less than six months of age eat 2–4% of their weight each day. Solid feeds are placed into three categories: forages (such as hay and grass), concentrates (including grain or pelleted rations), and supplements (such as prepared vitamin or mineral pellets). Equine nutritionists recommend that 50% or more of the animal's diet by weight should be forages. Hay can be analyzed by many laboratories and that is the most reliable way to tell the nutritional values it contains. Production quality also matters. If hay is baled with too much moisture, or if a dead animal, such as a snake or rodent, is caught in a bale, the subsequent botulism toxins released can contaminate the hay. Haylage, also known as Round bale silage is a term for grass sealed in airtight plastic bags, a form of forage that is frequently fed in the United Kingdom and continental Europe, but is not often seen in the United States. Because haylage is a type of silage, hay stored in this fashion must remain completely sealed in plastic, as any holes or tears can stop the preservation properties of fermentation and lead to mold or spoilage. Rodents chewing through the plastic can also spoil the hay introducing contamination to the bale. It is sometimes used as a filler; it can slow down horses who eat their grain too fast, or it can provide additional fiber when the horse must meet most nutritional needs via concentrated feeds. Concentrates Grains Whole or crushed grains are a common form of concentrated feed for horses. Oats are the most popular grain for horses. Oats have a lower digestible energy value and higher fiber content than most other grains. They form a loose mass in the stomach that is well suited to the equine digestive system. They are also more palatable and digestible than other grains. Wheat is generally not used as a concentrate. However, wheat bran is sometimes added to the diet of a horse for supplemental nutrition, usually moistened and in the form of a bran mash. Mixes and pellets Many feed manufacturers combine various grains and add additional vitamin and mineral supplements to create a complete premixed feed that is easy for owners to feed and of predictable nutritional quality. Supplements The average modern horse on good hay or pasture with light work usually does not need supplements; however, horses subjected to stress due to age, intensive athletic work, or reproduction may need additional nutrition. Extra fat and protein are sometimes added to the horse's diet, along with vitamin and mineral supplements. Soybean meal is a common protein supplement, and averages about 44% crude protein. The protein in soybean meal is high-quality, with the proper ratio of dietary essential amino acids for equids. Cottonseed meal, linseed meal, and peanut meal are also used, but are not as common. ==Feeding practices==

Most horses only need quality forage, water, and a salt or mineral block. Actual amounts fed vary by the size of the horse, the age of the horse, the climate, and the work to which the animal is put. In addition, genetic factors play a role as some horse breeds tend to be easy keepers (good doers), which means that they can thrive on small amounts of food and are prone to obesity and other health problems if overfed, and other breeds tend to be hard keepers (poor doers), meaning that they are prone to be thin and require considerably more food to maintain a healthy weight. Veterinarians are usually a good source for recommendations on appropriate types and amounts of feed for a specific horse. Animal nutritionists are also trained in how to develop equine rations and make recommendations. There are also numerous books written on the topic. Feed manufacturers usually offer very specific guidelines for how to select and properly feed products from their company, and in the United States, the local office of the Cooperative Extension Service can provide educational materials and expert recommendations. Feeding forages Equids always require forage. When possible, nutritionists recommend it be available at all times, at least when doing so does not overfeed the animal and lead to obesity. It is safe to feed a ration that is 100% forage When beet pulp is fed, a ration of to is usually soaked in water for 3 to 4 hours prior to feeding in order to make it more palatable, and to minimize the risk of choke and other problems. It is usually soaked in a proportion of one part beet pulp to two parts water. Beet pulp is usually fed in addition to hay, but occasionally is a replacement for hay when fed to very old horses who can no longer chew properly. However, on modern irrigated pastures, they may have their nutritional needs for forage met in as little as three hours per day, depending on the quality of grass available. Another factor when feeding forages is the level of various non-structural carbohydrates (NSC), such as fructan. Too high an NSC level causes difficulties for animals prone to laminitis or equine polysaccharide storage myopathy (EPSM). NSC cannot be determined by looking at forage, but hay and pasture grasses can be tested for NSC levels. Feeding concentrates Concentrates, when fed, are recommended to be provided in quantities no greater than 1% of a horse's body weight per day, Equine gastric ulcer syndrome is linked to a too-high concentration of grain in the diet, particularly noticed in modern racehorses, where some studies show such ulcers affecting up to 90% of all race horses. In general, the portion of the ration that should be grain or other concentrated feed is 0-10% grain for mature idle horses; between 20-70% for horses at work, depending on age, intensity of activity, and energy requirements. Access to water Horses normally require free access to all the fresh, clean water they want, and to avoid dehydration, should not be kept from water longer than four hours at any one time. However, water may need to be temporarily limited in quantity when a horse is very hot after a heavy workout. As long as a hot horse continues to work, it can drink its fill at periodic intervals, provided that common sense is used and that an overheated horse is not forced to drink from extremely cold water sources. But when the workout is over, a horse needs to be cooled out and walked for 30–90 minutes before it can be allowed all the water it wants at one time. However, dehydration is also a concern, so some water needs to be offered during the cooling off process. A hot horse will properly rehydrate while cooling off if offered a few swallows of water every three to five minutes while being walked. Sometimes the thirst mechanism does not immediately kick in following a heavy workout, which is another reason to offer periodic refills of water throughout the cooling down period. Ponies easily become obese from overfeeding and are at high risk for colic and, especially, laminitis. Fresh grass is a particular danger to ponies; they can develop laminitis in as little as one hour of grazing on lush pasture. Incorrect feeding is also as much a concern as simple overfeeding. Ponies and miniatures need a diet relatively low in sugars and starches and calories, but higher in fibers. Miniature horses in particular need fewer calories pound for pound than a regular horse, and are more prone to hyperlipemia than regular horses, and are also at higher risk of developing equine metabolic syndrome. If mules are fed concentrates, they only need about half of what a horse requires. Like horses, mules require fresh, clean water, but are less likely to over-drink when hot. They only need to eat 1.5% of their body weight per day in dry matter. It is not fully understood why donkeys are such efficient digestors, but it is thought that they may have a different microbial population in the large intestine than do horses, or possibly an increased gut retention time. Donkeys do best when allowed to consume small amounts of food over long periods, as is natural for them in an arid climate. They can meet their nutritional needs on 6 to 7 hours of grazing per day on average dryland pasture that is not stressed by drought. If they are worked long hours or do not have access to pasture, they require hay or a similar dried forage, with no more than a 1:4 ratio of legumes to grass. They also require salt and mineral supplements, and access to clean, fresh water. Like ponies and mules, in a lush climate, donkeys are prone to obesity and are at risk of laminitis. Treats Many people like to feed horses special treats such as carrots, sugar cubes, peppermint candies, or specially manufactured horse "cookies." Horses do not need treats, and due to the risk of colic or choke, many horse owners do not allow their horses to be given treats. There are also behavioral issues that some horses may develop if given too many treats, particularly a tendency to bite if hand-fed, and for this reason many horse trainers and riding instructors discourage the practice. However, if treats are allowed, carrots and compressed hay pellets are common, nutritious, and generally not harmful. Apples are also acceptable, though best if cored or sliced, as the seeds contain toxins. Horse "cookies" are often specially manufactured out of ordinary grains and some added molasses. They generally will not cause nutritional problems when fed in small quantities. However, many types of foods are potentially dangerous to a horse and should not be fed. This includes bread products, meat products, potatoes, brassicas, stone fruits, chocolate, and caffeinated beverages. It was once a common practice to give horses a weekly bran mash of wheat bran mixed with warm water and other ingredients. It is still done regularly in some places. While a warm, soft meal is a treat many horses enjoy, and was once considered helpful for its laxative effect, it is not nutritionally necessary. An old horse with poor teeth may benefit from food softened in water, a mash may help provide extra hydration, and a warm meal may be comforting in cold weather, but horses have far more fiber in their regular diet than do humans, and so any assistance from bran is unnecessary. There is also a risk that too much wheat bran may provide excessive phosphorus, unbalancing the diet, and a feed of unusual contents fed only once a week could trigger a bout of colic. ==Feed storage==

All hay and concentrated feeds must be kept dry and free of mold, rodent feces, and other types of contamination that may cause illness in horses. (See § Illnesses related to improper feeding below) It is generally not safe to give a horse feed that was contaminated by the remains of a dead animal. This is a potential source of botulism. This is not an uncommon situation. For example, mice and birds can get into poorly stored grain and be trapped; hay bales sometimes accidentally contain snakes, mice, or other small animals that were caught in the baling machinery during the harvesting process. ==Feeding behavior==

Horses can become anxious or stressed if there are long periods of time between meals. They also do best when they are fed on a regular schedule; they are creatures of habit and easily upset by changes in routine. When horses are in a herd, their behavior is hierarchical; the higher-ranked animals in the herd eat and drink first. Low-status animals, who eat last, may not get enough food, and if there is little available feed, higher-ranking horses may keep lower-ranking ones from eating at all. Therefore, unless a herd is on pasture that meets the nutritional needs of all individuals, it is important to either feed horses separately, In some situations where horses are kept together, they may still be placed into separate herds, grouping horses together based upon having similar nutritional needs. ==Dental issues==

Horses' teeth continually erupt throughout their life, are worn down as they eat, and can develop uneven wear patterns that can interfere with chewing. For this reason, horses need a dental examination at least once a year, and particular care must be paid to the dental needs of older horses. The process of grinding off uneven wear patterns on a horse's teeth is called floating and can be performed by a veterinarian or a specialist in equine dentistry. ==Illnesses related to improper feeding==

Colic, choke, and laminitis can be life-threatening when a horse is severely affected, and veterinary care is necessary to properly treat these conditions. Other conditions, while not life-threatening, may have serious implications for the long-term health and soundness of a horse. Colic Horse colic itself is not a disease, but rather a description of symptoms connected to abdominal pain. Colic is most often caused by a change in diet, either a planned change that takes place too quickly, or an accidental change, such as a horse getting out of its barn or paddock and ingesting unfamiliar plants. But colic has many other possible triggers including insufficient water, an irregular feeding schedule, stress, and illness. Because the horse cannot vomit and has a limited capacity to detoxify harmful substances, anything upsetting to the horse must travel all the way through the digestive system to be expelled. Choke Choke is not as common as colic, but is nonetheless commonly considered a veterinary emergency. The most common cause of choke is horses not chewing their food thoroughly, usually because of eating their food too quickly, especially if they do not have sufficient access to water, but also sometimes due to dental problems that make chewing painful. It is exceedingly difficult for a horse to expel anything from the esophagus, and immediate treatment is often required. Unlike choking in humans, choke in horses does not cut off respiration. Laminitis Horses are also susceptible to laminitis, a disease of the lamina of the hoof. Laminitis has many causes, but the most common is related to a sugar and starch overload from a horse overeating certain types of food, particularly too much pasture grass high in fructan in early spring and late fall, or by consuming excessive quantities of grain. Growth disorders Young horses that are overfed or are fed a diet with an improper calcium:phosphorus ratio over time may develop a number of growth and orthopedic disorders, including osteochondrosis (OCD), angular limb deformities (ALD), and several conditions under the umbrella of the developmental orthopedic diseases (DOD). If not properly treated, damage can be permanent. However, they can be treated if caught in time, given proper veterinary care, and any improper feeding practices are corrected. Young horses being fed for rapid growth in order to be shown or sold as yearlings are at particularly high risk. Adult horses with an improper diet may also develop a range of metabolic problems. Heaves Moldy or dusty hay fed to horses is the most common cause of Recurrent airway obstruction, also known as COPD or "heaves,” a chronic condition of horses involving an allergic bronchitis. Tying up Equine exertional rhabdomyolysis, also known as "tying up" or azoturia, is a condition to which only some horses are susceptible and most cases are linked to a genetic mutation. In horses prone to the condition, it usually occurs when a day of rest on full grain ration is followed by work the next day. This pattern of clinical signs led to the archaic nickname "Monday morning sickness". The condition may also be related to electrolyte imbalance. Proper diet management may help minimize the risk of an attack. ==See also==