Ideally, horses should be given free access to hay and/or pasture forages with salt and water free choice. Most horses fed good-quality forages require little to no concentrate supplementation. Exceptions are hard-working horses or those with limited access to good-quality forage (<2% body weight in feed dry matter).
Feeding more than 50% of the ration dry matter in the form of high starch/sugar concentrates to otherwise healthy adult horses has been documented to increase the risk of laminitis and colic. Horses should not be offered >0.5% of their body weight in high starch/sugar grain-based concentrates (eg, textured grain, pellets, or extruded feed) in a single feeding. More than this in a single meal reduces digestive efficiency and may contribute to the formation of gastric ulcers and insulin resistance in addition to laminitis and colic. If large amounts of grain-based concentrates are being fed, the total amount offered daily should be divided into two or more feedings. Large (>0.25% body weight) meals of grain-based concentrates should not be offered <1 hour before strenuous exercise, transport, or other stress, or to exhausted horses with poor gut motility.
Because horses are particularly sensitive to toxins found in spoiled feeds, all grains, concentrates, and roughages should be of good quality and free of mold. In warm, humid regions, mold inhibitors such as propionic acid may help reduce feed spoilage. In contrast, excessively dry, dusty feeds may initiate or aggravate respiratory problems. Dampening or soaking such feeds in water before feeding in a meal can help alleviate this problem. However in hot, humid climates, the moistened feeds should not exceed what the horses will eat in 1–2 hours to avoid mold growth.
Good pasture (which assumes adequate forage coverage) provides both an excellent source of nutrients and the opportunity to exercise. Pastures should be kept as free of weeds as possible by regular mowing. If practical, manure should be removed regularly to prevent uneven utilization. A legume-grass mixture offers the advantages of good nutrient supply, persistence, and durability. Ideal mixes vary with region, and local recommendations from agricultural extension and other specialists should be followed. In intensive management areas (small acreages), a general recommendation is 1 acre per horse for at least spring to fall if not supplementing other than salt and water. If supplementing with hays or concentrates, restricting access for at least part of the day, and practicing pasture rotation, more dense populations are possible. On extensive properties (ranches, ranges), the above recommendations are not practical, and acreage per horse may need to be greater.
Some forages should not be used for horse pastures under any conditions. Alsike clover(Trifolium hybridum) and kleingrass(Panicum coloratum) are potentially hepatotoxic to horses and need to be avoided. Johnson grass(Sorghum halepense) and Sudan grass(S sudanense) contain cyanogenic glycosides and Buffel (Cenchrus spp), panic (Panicum spp), pangola (Digitaria decumbens), kikuyu(Pennisetum spp), and Setaria spp grasses all contain potentially harmful concentrations of oxalates. None of these forage species should be used for horse pastures if possible, and, if present, attention to calcium intake is essential.
In sandy areas, horses should be provided with supplemental hay when pasture is short (ie, overgrazed) to prevent sand ingestion and subsequent colic. Hay should be offered in feeders with mats under them to reduce sand ingestion. The use of psyllium products to enhance the elimination of sand from the equine GI tract can be expensive, and efficacy has not been well documented. Supplemental hay is also recommended in any situation when the pasture is limited in quality (lots of weeds, undesirable weeds) or quantity to avoid weed ingestion and preserve the pasture cover.
Common types of hay used to feed horses include grass hays, such as timothy, brome, coastal Bermuda, orchard grass, or teff, and legumes such as alfalfa or clover.
In general, grass hays provide moderate protein, energy, and mineral contents. If harvested late, the protein content may be inadequate (<8.0% DM). Hays harvested from acidic soils may be deficient in calcium and/or selenium. Coastal Bermuda grass has been associated with an increased risk of impaction colic, especially if harvested when overly mature. Oat hay has been used in some regions of the USA and, if properly harvested and baled, is roughly equivalent to other grass hays.
Warm season grasses, such as teff, coastal Bermuda, Brachiaria, and Setaria spp, are used in some regions of the world and increasingly in the USA. However, they may be deficient in calcium or contain high levels of oxalates that will interfere with calcium uptake. Still, warm season grasses are consistently lower in starch, sugars, and fructans than the cool grass hays (timothy, orchard grass, brome), so they may be a consideration for horses with metabolic problems such as equine metabolic syndrome and pituitary pars intermedia dysfunction. Use in lactating mares and rapidly growing young horses is not recommended unless supplemented with calcium and protein.
Legume and legume/grass mixtures generally contain more protein, minerals, and vitamins than do grass hays. However, they may be more difficult to cure in warm, humid climates and are more prone to mold. Alfalfa also may be contaminated with blister beetles (lethal to horses) if grown in the western states of the USA and also tends to be more allergenic than grass hays or clover. However, alfalfa is an excellent source of nutrition and usually is recommended, at least as a supplement, for horses with increased protein and calcium needs.
The form in which harvested forages are provided to horses is variable. Dried hays (>90% dry matter) either baled in small (22–30 kg) or large (more than 200 kg) bales are most commonly used. Feeding large, round bales of hay in pastures can be economically advantageous, but it has been documented to increase the risk of botulism and to have high wastage if not protected by a feeder of some sort and in a feeder that keeps the bale off the ground.
High-moisture (65% dry matter or less) haylages and silages are also used, especially in areas where harvesting good quality dried hays is difficult. Those made from whole corn plants, which are commonly fed to cattle, should be used with extreme caution because of the risk of mold. Moldy corn silage causes fatal leukoencephalomalacia in equine animals. Sorghum or other grass high moisture (50% or higher) haylages and silages have been used as forage substitutes for horses, but the hygienic quality (absence of molds) is still of concern.
Cubed or chopped forages are often recommended as substitutes for long-stem hay or pasture and for horses that have trouble chewing. Forage-based cubes or pellets may need to be soaked in water to decrease the risk of choke for some horses.
Forage-based total mixed rations and "complete" feeds, which may have concentrates added, have been developed for horses. These can be textured, pelleted, cubed, or extruded products. They have the advantage of uniform quality, complete control over nutrient intake, suitability for horses with bad teeth, less dustiness (which reduces respiratory problems), and reduced bulk for storage and transport. Disadvantages include an increased risk of choke and increased wood chewing, especially with the textured, pelleted, and extruded feeds fed as the sole source of nutrition. Most of the textured, pelleted, and extruded products are not designed to be fed free choice, so if the sole source of nutrition, should be provided in multiple smaller feedings or with some sort of forage. Wood chewing and boredom can be minimized by feeding long-stem hay with these products or by dividing the total daily allotment into multiple small feedings.
Concentrates include all grains and commercial grain byproduct feeds that are high in energy and/or protein meant to be fed in 1 or more kg per day in addition to forages. Processing grains before feeding is often desirable to improve nutrient availability. However, cracked or rolled grains are more susceptible to mold. Because of differences in density, grain and commercial, grain-based concentrates should be measured by weight, not volume.
Most grains and grain-based concentrates are >25% nonstructural carbohydrates, which are rapidly digested into the component sugars and absorbed in the small intestine. Though excellent sources of quick energy, high sugar/starch (>30% nonstructural carbohydrate) rations have been documented to induce high insulin responses and may be associated with increased incidence of vices such as wind sucking and wood chewing, especially if >25% of the total ration. If not needed to provide extra calories or other nutrients, they are usually not necessary if adequate forage or hay is available and the animal has normal dentition. All grains are deficient in calcium, and high-grain rations need to be supplemented with additional calcium supplements (legumes or commercial concentrates or supplements). It is important to read the labels of commercial concentrates to determine content and purpose.
Oats, one of the most traditional grains for horses, may be fed whole, rolled, crimped, or hulled (naked). They are the highest in protein (~12%) and fiber but lowest in Mcal/kg of the commonly used grains if the hulls are included.
Processing improves digestibility by ~10%. “Hulled” or “naked” oats are more energy dense than regular oats and should be introduced slowly to reduce the risk of founder or colic.
Barley is a good grain for horses, though not commonly used in many regions. It is higher in energy than hulled oats but lower than corn, but it causes a lower glycemic response than either corn or oats, making it the grain of choice for insulin-resistant horses that need supplementation. It may be fed as the only grain in addition to adequate forage to horses that have high energy needs. Barley should be rolled or crimped to improve digestibility. Palatability is not as high as that of oats or corn.
Corn (maize) is a high-energy feed, most useful for horses that are working hard or in need of extra weight gain. Though whole corn can be fed, to maximize digestibility, corn may be cracked or rolled, but the moisture level should be low enough to avoid spoilage during storage. The starch in corn is less digestible than that of oats or barley and can more easily bypass small-intestinal digestion, resulting in colic and/or laminitis if suddenly fed in large amounts. It should be introduced slowly to a ration. Moldy corn can cause leukoencephalomalacia, which is usually fatal.
Sorghum grain (milo) and wheat should be fed with care. These grains must be cracked or rolled if fed to horses. They are not commonly used in horse rations.
Other concentrate sources of energy/protein used in various regions of the world include dried peas (Great Britain), sugar cane pulp (Brazil), fava beans (Middle East), and bread. Be aware that bakery waste additives such as sesame, poppy seeds, or chocolate might cause positive drug-test reactions in performance horses.
Wheat bran and rice bran are grain byproduct supplements commonly fed to horses. However, both are very high in phosphorus (>1.2%), and the proper calcium:phosphorus ratio in the total ration should be maintained when any form of bran is added.
Wheat bran is not laxative, contrary to popular belief, but is extremely palatable to horses and often used as a wet “mash” to increase water intake or mask the flavor of other supplements. Because of its high phosphorus content, wheat bran is not recommended as a major or daily component of the ration unless the calcium intake is carefully balanced.
Rice bran is a high-fat product added to rations of horses that need extra calories. Many rice bran products have added calcium to offset the high phosphorus content but still are designed to be fed in only limited (<1 kg/day) amounts.
Beet pulp, a byproduct of the sugar beet industry, is added to horse rations as both a source of calories and fiber. It contains moderate amounts of calcium and protein and can be safely fed on a daily basis in larger amounts than the bran products. Shredded beet pulp usually should be soaked in water before feeding to horses. Beet pulp pellets do not require pre-soaking and are often included in concentrate mixes. Beet pulp products may or may not contain added molasses. If feeding as a major fiber source to horses with insulin resistance, beet pulp products without added molasses should be used but may not be palatable.
Edible oils and fats may be added to rations to increase the energy density. Normal horse rations contain only 3%–4% fat, but horses can easily tolerate up to 10% fat in the total ration if it is introduced slowly and they are given 3–4 weeks to fully adapt to the change. Corn, soy, and other edible oils are commonly used. Although highly digestible, animal fat is not commonly used in horse rations.
Soybean meal is a palatable protein supplement with good amino acid balance for use in concentrate mixes. It may be fed when the pastures or hays available are low in protein and/or are of poor quality or when protein requirements are greatest, such as during early growth or lactation.
Linseed meal or cottonseed meal should not be used as protein supplements for young, growing horses because of their low lysine content, but they are adequate for adult horses, if needed.
Cane molasses is frequently added to grain mixtures (sweet feeds). It is highly palatable, minimizes separation of “fines,” and reduces dustiness of concentrate mixtures. It is also high in potassium, which means it should be avoided in feeds for horses with hyperkalemic periodic paralysis. The readily fermentable carbohydrates and moisture that cane molasses provides also may increase mold growth in hot weather and freeze solid in cold winter weather.
Limestone of a high grade (38% calcium) may be used as a supplemental source of calcium.
When both supplemental calcium and phosphorus are needed, dicalcium phosphate, steamed bone meal, or defluorinated rock phosphate are recommended. Dicalcium phosphate is particularly good because the cost per unit of phosphorus is low, the elements are quite available, and it is fairly palatable.
Individual differences in the need for energy and nutrients and gross variations in nutrient contents of feedstuffs make it difficult to generalize about the amount of feed to provide. Body condition and overall health should be monitored, and amounts fed should be adjusted accordingly. The maximal dry matter intake in 24 hours is only 3%–3.5% of a horse’s body weight, and many horses (especially late-pregnant mares) voluntarily consume <2.5% of their body weight in dry matter in 24 hours. Feed intake should therefore be monitored.
The need for concentrate supplementation while on pasture depends on pasture quality but is more important for young horses and lactating mares. If the pasture is of good to excellent quality, no supplementation other than water and salt are needed by most adult horses at maintenance or in light work. If forage quality is poor, it is desirable to creep-feed nursing foals at the rate of 0.5%–1% body weight with concentrates formulated specifically for growth.