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'''Equine nutrition''' refers to the feeding of [[horse]]s, [[pony|ponies]], [[mule]]s, [[donkey]]s and other [[equid]]s. Correct and balanced nutrition is a critical component of proper [[horse care]]. |
'''Equine nutrition''' refers to the feeding of [[horse]]s, [[pony|ponies]], [[mule]]s, [[donkey]]s and other [[equid]]s. Correct and balanced nutrition is a critical component of proper [[horse care]]. |
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[[Category:Horse management]] |
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Revision as of 17:24, 14 February 2007
Equine nutrition refers to the feeding of horses, ponies, mules, donkeys and other equids. Correct and balanced nutrition is a critical component of proper horse care.
Horses are non-ruminant herbivores, also known as "hind-gut fermentors." Put simply, horses have only one stomach, similar to humans. However, they also have to digest plant fiber from grass and hay. Unlike ruminants who digest fiber in plant matter by use of a multichambered stomach, horses use bacterial fermentation that occure in the "hind gut" known as the cecum (or caecum) to break down cellulose. The horse digestive system is also unique in that horses do not possess a gall bladder, and thus bile flows steadily into the small intestine from the liver and is not stored.
In practical terms, horses prefer to eat small amounts of food steadily throughout the day, as they do in nature when grazing on pasture. Although this is not always possible with modern management techniques that favor feeding horses twice a day, it is important to remember the underlying biology of the animal when determining what to feed and in what quantities.
Horses are also very susceptible to colic. It is very important that horses be fed clean, high-quality feed at regular intervals and not be subjected to abrupt changes in their diets. Because horses are sensitive to molds and fermentation toxins, they also should never be fed silage or things like fresh lawn clippings.
The digestive system
The digestive system of the horse is somewhat sensitive. Because horses are unable to regurgitate food, if they overeat or eat something poisonous, vomiting is not an option. Unfortunately, horse colic is a common problem and one of the leading causes of death in horses.
Oral cavity
Digestion begins in the oral cavity. The incisors of the horse clip forage, which is then pushed back in the mouth by the tongue, and grinded by the premolars and molars. The canines of the horse (should the animal have them) play no part in chewing food.
When swallowing occurs, the soft palate (a flap of tissue in the back of the mouth) closes over the pharynx of the animal, which prevents food from going down the trachea, but momentarily prevents the horse from being able to breathe. This soft palate is also the reason why horses can not breathe through their mouth when they are in respiratory distress.
The esophagus
The esophagus is usually 4-5 feet in length, and carries the food from the oral cavity to the stomach. Due to the coronary sphincter, the esophagus only allows the passage of food in one direction. It is also the area of the digestive tract where horses get choke, or esophageal obstruction, due to eating something that is too large to pass down the length of the esophagus. Therefore, unlike humans, equine choke does not prevent the animal from breathing, but is still a very serious problem that can eventually lead to pneumonia if left untreated.
The stomach
Horses and other Equids evolved as grazing animals, adapted to eating small amounts of food all day long. Therefore, they have a relatively small stomach for their size. The average sized horse (800 to 1200 lbs) has a stomach with a capacity of 2 to 4 gallons, and works best when it is 2/3 full. This limits the amount of feed a horse can take in at one time, and makes it important for horses to have several small meals or continuous access to forage, as opposed to one or two large meals a day.
The food arrives into the stomach from the esophagus through the coronary sphincter. The majority of gastric juice is made up of hydrochloric acid, which turns pepsinogen into the enzyme pepsin. Pepsin allows for the partial breakdown of proteins. Other enzymes include resin and lipase. Additionally, the stomach absorbs some water, as well as ions and lipid soluble compounds. The main purpose of the stomach, however, is to break down food into chyme.
Food then leaves the stomach through the pyloric valve, which controls the flow of food out of stomach.
The small intestine
The horse’s small intestine is 50 to 70 feet long and holds 10 to 23 gallons. It consists of 3 parts, the duodenum, jejunum, and ileum, and has several small projections from its tissue called villi, which help to increase the surface area of the intestine and therefore the absorbance efficiency. Digestion of protein, some carbohydrates and fat occurs here, as does the absorption of most vitamins and minerals.
Additionally, the pancreas and liver both play a role in the small intestine, by secreting a very alkaline digestive juice about 5-6 inches from the pyloric valve. This counteracts the acidity of the chyme from the stomach and prevents it from eating through the tissue of the intestine.
The cecum and large intestine
Most liquids are passed to the cecum, also known as the "water gut" or "hind gut." It is a cul-de-sac pouch, about 3 to 4 feet long and holds 7 to 8 gallons. Detoxification of toxic substances occurs in the cecum. It also contains bacteria and protozoa that digest plant fiber (through fermentation) and any soluble carbohydrates. Horses must have their diets changed slowly so that the bacteria in the cecum are able to modify and adapt to the different chemical structure of new feedstuffs. Too abrupt a change in diet can cause colic, as the new food is not properly digested.
The large colon, small colon, and rectum make up the large intestine. The large colon is 10 to 12 feet long, with a diameter of 8-10", and holds 14 to 16 gallons. Its main purpose it 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 leads is 10-12 feet in length and holds only 5 gallons of material. It is the area where the majority of water in the horse's diet is absorbed, and is also the place where fecal balls are formed.
The rectum is about 1 foot in length, and acts as a holding chamber for fecal matter, which is passed out the anus.
Nutrients
Equines require six main classes of nutrients to survive: water, fats, carbohydrates, proteins, vitamins, and minerals.
Water
Water is the single most important nutrient. Horses can only live about 72 hours without water. An average horse drinks 10 to 12 gallons of water per day, more in hot weather or when eating dry forage such as hay, less in cool weather or when on lush pasture. It is critically important that horses have an adequate clean supply of water. When under hard work, or for the lactating mare, water requirement may be 3 to 4 times the normal consumption.
Water is particularly important to digestion because the forages and grains horses eat are mixed with saliva in the mouth to make a moist bolus that can be easily swallowed. To accomplish this goal, horses produce up to 10 gallons (85 lb.) of saliva per day.
Energy nutrients
Nutritional sources of energy for horses are fat, carbohydrates and protein. Horses that are heavily exercised, growing, pregnant or lactating need increased energy in their diet.
Horses are unique in that they do not have a gall bladder. Therefore bile flows continuously from the liver directly into the stomach, making fat, though a necessary nutrient, difficult for horses to digest and utilize in large quantities. Horses can only make use of up to 15%-20% fat in their diet without ill effects. Above this amount, horses may develop diarrhea. Normal horse rations contain only 3 to 4% fat.
Fat exists in low levels in some plants and can be added to a feed to increase the energy density of the diet. Fat has 9 Mcal/kg of energy, which is three times that of any carbohydrate source.
Carbohydrates, usually fed in the form of hay, grass and grain, are the main energy source used in most feeds. The main building block of carbohydrates is glucose. Soluble carbohydrates such as starches and sugars are readily broken down to glucose in the small intestine and absorbed. Insoluble carbohydrates such as fiber (cellulose) bypass enzymatic digestion and must be fermented by microbes in thececum and large intestine to release their energy sources, the volatile fatty acids.
Soluble carbohydrates are found in nearly every feed source; corn has the highest amount, then barley and oats. Forages normally have only 6 to 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 colic or laminitis.
Protein is used in muscle development during growth or exercise. 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 to 10% protein in their diet; however, higher protein is important for lactating mares and young growing foals.
Vitamins and minerals
Horses that are not subjected to hard work or extreme conditions usually have more than adequate amounts of vitamins in their diet if they are receiving fresh green forage and/or premixed rations. Horses sometimes need a vitamin supplement when feeding low-quality hay, if a horse is under stress (traveling, showing, racing, etc.), or not eating well due to illness. Most of the vitamins used by horses are found in green, leafy forages, so a very high-grain diet also requires specialized supplementation to prevent an imbalance of vitamins and minerals.
Minerals are required for maintenance of body structure, fluid balance in cells (electrolytes), nerve conduction, and muscle contraction. Minerals such as calcium, phosphorus, sodium, potassium, chloride, andmagnesium are needed daily, but are commonly found in most good-quality feeds.
Calcium and phosphorus are needed in a specific ratio ideally 2:1, but never less than 1:1. Normally, if adult horses are consuming fresh green pasture and/or a premixed ration, they will receive proper amounts of minerals in their diet, with the exception of sodium chloride (salt), which should always be available. Young horses may need added calcium, phosphorus, copper, and zinc during the first year or two of life. Sweating depletes sodium, potassium, and chloride from the horse’s system, therefore, supplementation with electrolytes may be helpful for horses in intense training, especially in hot weather.
Types of feed
Horses and other equids can consume approximately 1.5 to 2% of their body weight in dry feed each day. Foals less than six months of age eat 2 to 4% of their live weight. Therefore, a 1000 lb adult horse could eat up to 20 pounds of food. Most of the animal's diet by weight should consist of forages. However, if a horse is working hard and requires more energy, the use of grain is increased and the percentage of forage decreased so that the horse obtains the nutrient balance it needs for the work it is performing.
Forages
Forages, also known as "roughage," are plant materials classified as legumes or grasses. Both can be found in pastures or in hay. Nutrients available in forage vary greatly with maturity of the grasses, fertilization, management, and environmental conditions.
Grasses are tolerant of a wide range of conditions and contain most necessary nutrients. Some commonly used grasses include orchard grass, brome, timothy, bluegrass, and fescue. Grasses alone are quite adequate nutritionally for mature horses who are not subjected to intense work.
Legumes such as clover or alfalfa are usually higher in protein, calcium, and energy than grasses. However, they require warm weather and good soil to produce the best nutrients. Legume hays are generally higher in protein than the grass hays. They are also higher in minerals, but have an incorrect ratio (often 5:1) of calcium to phosphorus. Because they are high in protein, they are very desirable for growing horses or those subjected to very hard work, but the calcium-phosphorus ratio must be balanced by other feeds to prevent bone abnormalities.
Often, pastures and hayfields will contain a bland of grasses and legumes.
Hay is forage that has been harvested, dried, and baled before feeding to horses. Hay is most nutritious when cut earlier in the plant growth stage. Maturity at harvest and quality of processing are the key to quality. Hay that is very green can be a good indicator of the amount of nutrients in the hay, however, color should not be used as sole indicator, smell and texture are also important. Hay can be nutritionaly analyzed by many laboratories and that is the most reliable way to tell the nutritional values it contains. Moldy or dusty hay should not be fed to horses.
Concentrates
Grains
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 horse's digestive system. They are also more palatable and digestible for horses than other grains.
Corn is the second most palatable grain for horses. It provides twice as much digestible energy as an equal volume of oats and is low in fiber. Because of these characteristics, is easy to over feed corn, causing obesity, so horses are seldom fed corn all by itself. Moldy corn should never be fed because it is lethal to horses.
Sorghum and Barley are also fed to horses, but need to be processed to allow easier digestibility. Wheat is generally not used as a concentrate because of cost and because its small hard seeds are difficult for horses to digest. However, wheat bran and wheat germ oil are sometimes added to the diet of a horse for supplemental nutrition.
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. Some of these prepared feeds are manufactured in pelleted form, others retain the grains in their original form, using molasses as a binder to keep the feed mixed and for increased palatability.
Supplements
Extra fat and protein are often added to the horse's diet, along with vitamin and mineral supplements. A horse on good hay or pasture with light work probably does not need feed supplements, however, horses subjected to stress due to age, intensive athletic work, or reproduction may need additional nutritional support.
Soybean meal is the most common protein supplement, which averages around 44% crude protein. The protein in soybean meal is usually a high-quality protein with the proper ratio of dietary essential amino acids for equids. Cottonseed meal, Linseed meal, and peanut meal are also used, but not as often.
Brewer’s grains (the mash removed from the malt when making beer) are a byproduct of the brewing industry. Horses find this product palatable, and it is about 25% crude protein, high in fat (13%) and contains B vitamins.
Vegetable oil is the most commonly used fat source in horse feeds. Corn oil is particularly popular, but others are used as well. Rice bran is a newer fat supplement on the market. It is distributed by many commercial feed dealers. Ground flax seed is another good source of fat, though it must be carefully processed, and some commercial feed manufacturers now make products containing both flax seed and rice bran.
There are hundreds of vitamin and mineral supplements on the market, many tailored to horses with specialized needs.
How to feed
Horses were designed to eat small amounts often. If at all possible, roughage should be available all the time, when doing so does not overfeed the horse and lead to obesity. A feed ration should be at least 50% roughage. If a ration needs to contain a higher percent of concentrates than 50%, such as for a race horse, bulky grains such as oats should be used as much as possible. In general, the portion of the ration that should be grain is as follows:
- 0 to 10% grain for mature idle horses
- 20 to 70% for horses at work, depending on intensity of activity and energy requirements.
Feeding Guidelines (adapted from Rutgers University Equine Science Center): To maintain body weight, most horses need only good forage, water, and a salt/mineral block.
- Always try to feed the most forage possible then add concentrate.
- Feed by weight not volume (1 lb. of Oats has a different volume than 1 lb. of Corn)
- Concentrates, if used, should be fed at least twice a day with no more than 0.5% body weight per feeding.
- Store feed properly: it should be kept free of mold, rodents, or contamination.
- Keep Ca:P ratios around 2 parts Calcium to 1 part Phosphorus.
- Feed on a set schedule (horses are creatures of habit and are easily upset by changes in routine).
- Change feeds gradually (horses’ stomachs cannot cope with drastic changes in feed; it could cause colic).
- When work or exercise decreases, decrease the grain. Additionally, cut back grain on days that the horse is not worked (it is usually recommended to reduce it by half), especially if the horse is receiving a large amount of grain. Failure to do so could lead to Equine Exertional Rhabdomyolysis, or "tying up," a very serious muscular problem.
While horses should normally have free access to all the fresh, clean water they want, water needs to be temporarily limited when a horse is hot after a heavy workout. As long as a hot horse continues to work, it can drink its fill; however, a hot horse that has ceased work needs to be cooled out for 30—90 minutes before it can be allowed all the water it wants at one time. A hot horse can be given two or three swallows of water every three to five minutes during the cooling process while being walked out.
Management considerations
- When horses are in a herd with a limited food source, their behavior is hierarchical; the higher-ranked animals in the herd eat first, and sometimes low-status animals may not get to eat at all. Unless the herd is on pasture that meets all their nutritional needs, it is important to either feed horses separately or spread their feed out in separate feeders to be sure all animals get to eat.
- Horses' teeth continually grow throughout their life, are worn down as they eat, and can develop uneven wear patterns that can interfere with chewing. For this reason, all horses' teeth need to be examined at least once a year, and particular care must be paid to the dental needs of older horses.
- In addition to horse colic, which can occur due to any number of digestive upsets, from mild bloating due to excess intestinal gas to life-threatening impactions, horses are also susceptable to laminitis, an inflammation of the lamina of the hoof. Laminitis has many causes, but the most common is related to a horse severely overeating, particularly fast-growing pasture grasses in early spring or by getting into unlimited quantities of grain. Both colic and laminitis can be life-threatening conditions when a horse is severely affected.
- Foals and 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 contain other key nutrients. A number of skeletal problems may occur in young horses with an unbalanced diet or one overloaded with calories.
References
- Budiansky, Stephen. The Nature of Horses. Free Press, 1997. ISBN 0-684-82768-9
- "Horse Nutrition." Bulletin 762-00, Ohio State University. Web site accessed February 9, 2007.
- Carey A.,Ph.D., Extension Specialist. "The Basics of Equine Nutrition" from FS #038, Equine Science Center, Rutgers University, Revised: April 2004. Web site accessed February 9, 2007