Equine nutrition

[1] In practical terms, horses prefer to eat small amounts of food steadily throughout the day, as they do in nature when grazing on pasture lands.

[4] Therefore, horses require clean, high-quality feed, provided at regular intervals, plus water or they may become ill if subjected to abrupt changes in their diets.

[7][8] 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.

The esophagus enters the stomach at an acute angle, creating a one-way valve, with a powerful sphincter mechanism at the gastroesophageal junction, which is why horses cannot vomit.

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.

[1][11] The small colon is also 10 to 12 feet (3.0 to 3.7 m) long, holds about 5 US gallons (19 L), is the area where the majority of water is absorbed, and where fecal balls are formed.

[3] 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.

[citation needed] An average 1,000-pound (450 kg) horse drinks 10 to 12 US gallons (38–45 L) of water per day, more in hot weather, when eating dry forage such as hay, or when consuming high levels of salt, potassium, and magnesium.

Insoluble carbohydrates, such as fiber (cellulose), are not digested by the horse's own enzymes, but are fermented by microbes in the cecum and large colon to break down and release their energy sources, volatile fatty acids.

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 or laminitis.

[18] 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, leafy forages.

Sometimes a vitamin/mineral supplement is needed when feeding low-quality hay, if a horse is under stress (illness, traveling, showing, racing, and so on), or not eating well.

Normally, if adult animals at maintenance levels are consuming fresh hay or are on pasture, they will receive adequate amounts of minerals in their diet, with the exception of sodium chloride (salt), which needs to be provided, preferably free choice.

[27] 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.

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.

[33] 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.

Once touted for a laxative effect, this use of bran is now considered unnecessary, as horses, unlike humans, obtain sufficient fiber in their diets from other sources.

[43] Some animals are naturally 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.

Others are hard keepers (poor doers), meaning that they are prone to be thin and require considerably more food to maintain a healthy weight.

[1] [13] If a ration needs to contain a higher percent of concentrates, such as that of a race horse, bulky grains such as oats should be used as much as possible; a loose mass of feed helps prevent impaction colic.

A relatively uncommon, but usually fatal concern is colitis-X, which may be triggered by excess protein and lack of forage in the diet that allows for the multiplication of clostridial organisms, and is exacerbated by stress.

[33] Concentrates designed for horses, with added vitamins and minerals, will often provide insufficient nutrients at the small serving sizes needed for ponies.

[61] 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.

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.

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.

[69] Horses' teeth continually erupt throughout their life, are worn down as they eat, and can develop uneven wear patterns that can interfere with chewing.

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.

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.

[citation needed] 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.