Feeding Practices in Horses and Other Equids

Pasture Feed of Horses

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 autumn if not supplementing with other forages. If supplementing with hays or concentrates, restricting access for at least part of the day, and practicing pasture rotation, denser 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. None of these forage species should be used for horse pastures if possible, and, if present, attention to calcium intake is essential:

• 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.

• Buffel (Cenchrus spp), panic (Panicum spp), pangola (Digitaria decumbens), kikuyu (Pennisetum spp), and Setaria spp grasses all contain potentially harmful concentrations of oxalates.

Endophyte-infected tall fescue has been documented to cause abortion, dystocia, and poor milk production in pregnant mares and should be avoided during gestation (9).

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 decrease sand ingestion. Additionally, hay nets or other hay feeders may be used. The use of psyllium products to enhance the elimination of sand from the equine GI tract, while not known to be harmful, can be expensive, and efficacy has not been well documented. Supplemental hay and an appropriate ration balancer are also recommended in any situation when pasture is limited in quality (lots of weeds, undesirable weeds) or quantity to avoid weed ingestion and preserve the pasture cover.

Hays and Other Preserved Forages for Feeding Horses

Common types of hay used to feed horses include grass hays, such as timothy, brome, coastal Bermuda, orchard grass, and teff, and legumes such as alfalfa.

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 can be deficient in calcium and/or selenium. Coastal Bermuda grass should be harvested prior to maturity because overmature cuttings have been associated with an increased risk of impaction colic. Oat hay has been used in some regions of the US and, if properly harvested and baled, is roughly equivalent to other grass hays.

Warm-season grasses, such as teff, Bermuda grass, Brachiaria, and Setaria spp, are used in some regions of the world and increasingly in the US. However, they can 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 cool grass hays (timothy, orchard grass, brome), so they could be a consideration for horses with metabolic problems (eg, 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, which is easily achieved via a ration balancer.

Legume and legume/grass mixtures generally contain more protein, minerals, and vitamins than do grass hays alone. However, they can be more difficult to cure in warm, humid climates and are more prone to mold. Alfalfa also can be contaminated with blister beetles (lethal to horses) if grown in the western US. 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. It can also be beneficial in the dietary management of EGUS, because calcium and protein serve to help buffer gastric acid.

The form in which harvested forages are provided to horses is variable. Dried hays (> 88–90% dry matter), in either small bales (22–30 kg [49–66 pounds]) or large bales (more than 200 kg [440 pounds]), are most commonly used. Feeding large round bales of hay in pastures can be economically advantageous; however, this practice increases the risk for botulism. Round bale hay decomposes rapidly where it contacts the ground, leading to potential bacterial contamination and considerable wastage of the feed. (Note: The American Association of Equine Practitioners (AAEP) recommends the botulism vaccine for horses at risk of consuming forage that contains decaying plant matter, which can include round bales and haylage.)

High-moisture (< 65% dry matter) haylages and silages are also used, especially in areas where harvesting good-quality dried hays is difficult. This type of forage is more common in the UK and some other countries outside the US. Haylage and silage made from whole corn plants, which are commonly fed to cattle, are generally not recommended for horses 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; however, the hygienic quality (absence of molds) is still of concern. Nutritionists generally recommend avoiding these types of forages for horses because of the high risk of botulism toxins (10).

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 might need to be soaked in water to decrease the risk of choke for some horses. They make excellent sources of forage for horses with poor dentition.

Forage-based total mixed rations and "complete" concentrate feeds 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 poor dentition, less dustiness (which decreases respiratory problems), and decreased bulk for storage and transport. Disadvantages include an increased risk of choke, increased wood chewing, and lack of long-stem fiber, especially when textured, pelleted, and extruded feeds are fed as the sole source of nutrition.

Most textured, pelleted, and extruded products are not designed to be fed free-choice, so if they comprise the sole source of nutrition, they should be provided in multiple smaller feedings or with some sort of forage (ie, soaked forage cubes, soaked beet pulp). Wood chewing and boredom can be minimized by feeding long-stem hay, if the horse is able to properly chew it, either with these products or by dividing the total daily allotment into multiple small feedings. Using slow feeders can also extend consumption time.

Concentrates for Feeding Horses

Concentrate feeds are fed to horses when forage alone cannot meet energy and/or nutrient needs. Concentrates include all grains and commercial grain-based feeds that are high in energy and/or protein and meant to be fed in amounts of ≥ 1 kg/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. Concentrates should be fed according to the manufacturer's directions to ensure proper nutrient intake based on the body weight and activity level of the horse and should always be weighed for proper feeding amounts. If a horse is consuming less concentrate than recommended, the addition of at least a partial portion of a ration balancer might be necessary to ensure proper nutrient intake. If a horse is consuming more than recommended in order to maintain condition, a different concentrate with higher fat and calorie content could be warranted.

Some grains and grain-based concentrates are > 25% NSCs, which are rapidly digested into the component sugars and absorbed in the small intestine. Though excellent sources of quick energy, high-sugar/starch (> 30% NSC) 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 NSC products make up > 25% of the total ration. High-sugar and high-starch feeds are typically reserved for racehorses or other horses in very heavy work. High-carbohydrate feeds may also exacerbate clinical signs of EGUS.

High-performance horses need carbohydrates to support energy needs and recovery; otherwise, performance could suffer in healthy horses. Horses cannot "carb load" in the same way humans can, and it can take up to 3 days for complete glycogen replenishment to occur in the muscles after heavy work. Adding high-carbohydrate feedstuffs will not accelerate the process, and they should not be suddenly introduced if not a part of the regular diet.

Unless needed to provide extra calories or other nutrients, concentrates or grain might not be necessary if sufficient good-quality forage or hay is available and the animal has normal dentition. All grains (ie, corn, oats, barley) are deficient in calcium, and high-grain rations need to be supplemented with additional calcium supplements (legumes, commercial concentrates, beet pulp, or supplements) or a ration balancer. Commercial concentrates should be nutritionally balanced, but they are not interchangeable. 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 (approximately 12%) and fiber but lowest in Mcal/kg of the commonly used grains if the hulls are included. Rolled oats provide an average of 2.94 Mcal/kg, with whole oats ranging from slightly less to slightly more, on an as-fed basis. Oat hulls provide a prebiotic fiber that acts as a food source for the hindgut microbiome and are often used as a valuable fiber source in commercial concentrates.

Barley is a good grain for horses, though not as commonly used in many regions. It is higher in energy than hulled oats but lower than corn. In addition to adequate forage, if barley is fed as the only grain to horses with high energy needs, a ration balancer should be provided to balance nutrient intake. Barley should be rolled or crimped to improve digestibility. Palatability tends to be lower than that of oats and corn.

Corn (maize) is a high-energy feed but is lower in crude protein and lysine than oats and barley. Corn is commonly used to add energy (calories) to diets and is most useful for horses that are working hard or in need of extra energy. To maximize digestibility, corn must be cracked or rolled, but the moisture level should be low enough to avoid spoilage during storage. Whole corn cannot be digested by horses. Moldy corn can cause leukoencephalomalacia, which is usually fatal. Distillers' dried grains (DDGs), a by-product of corn fermentation to produce ethanol, are higher in protein than raw corn and are sometimes included in horse and other livestock feeds in limited amounts as a secondary protein source.

Sorghum grain (milo) and wheat should be fed with care, due to their reversed calcium:phosphorus ratio (like that other grains) and typically high starch content. These grains must be cracked or rolled if fed to horses. They are not commonly used in horse rations. However, wheat middlings, or midds (a by-product of wheat flour milling), are a very common ingredient for commercial horse feeds and are used for energy, as a secondary protein source, and as an effective natural pellet binder.

Other concentrate sources of energy/protein used in various regions of the world include dried peas (Great Britain, US), 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.

Other Supplements for Feeding Horses

Ration balancers are concentrated sources of protein, vitamins, and minerals that are typically low in calories, starch, and sugar. Ration balancers are designed to provide nutrients to equids with lower calorie requirements (ie, obese animals) or animals on forage-only diets. Ration balancers are also useful for supplementing nutrients to animals consuming poor-quality forage, recovering from illness, or following restricted diets. The feeding rate of a ration balancer is usually low—eg, 0.5–0.9 kg(1–2 pounds)/day of balancer for a 500-kg (1,100-pound) horse on a forage-only diet. To ensure proper overall nutrient intake, a decreased amount of a balancer can be added to diets of horses receiving a concentrate at a lower rate than recommended by the manufacturer.

Wheat bran and rice bran are grain by-product supplements commonly fed to horses because of bran's high fat and energy content. However, both are very high in phosphorus (> 1.2%) and low in calcium. Thus, the proper calcium:phosphorus ratio in the total ration should be maintained by providing a ration balancer or other source of calcium (eg, legume forage or beet pulp) 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. The common practice of providing a bran mash periodically (eg, every Sunday or on a cold day) should be avoided. Instead, if providing bran is desired, a small amount can be provided as a regular part of a balanced daily diet. Periodic, irregular supplementation with bran can cause digestive upset, which is commonly mistaken for a laxative effect, if the bran is given in sufficient quantities without dietary adaptation.

Rice bran is a high-fat product added to rations of horses that need extra calories. Many rice bran products are stabilized to prevent degradation and have added calcium to offset the high phosphorus content. However, rice bran is usually intended to be fed in only limited (< 1 kg/day) amounts. Rice bran is not a low-starch or low-sugar feed, so its inclusion in the diet of insulin-dysregulated horses should either be avoided or limited, using extreme caution and consulting with a qualified equine nutritionist.

Beet pulp, a by-product of the sugar beet industry, is added to horse rations as a source of both calories and fiber. It contains moderate amounts of calcium and is very low in starch and sugar (typically less than 10–12% on an as-fed basis). Beet pulp can be safely fed on a daily basis in larger amounts than bran products. Beet pulp (shreds or pellets) should be soaked in water before feeding to horses. Beet pulp products might or might not contain added molasses, but typically the total starch and sugar content remains below 12%. Contacting the manufacturer for starch and sugar analysis is recommended if that information is needed.

Edible oils and fats may be added to rations to increase energy density. Normal horse rations contain only 3–4% fat; however, horses can easily tolerate 10% fat in the total daily ration if it is introduced slowly and they are given 3–4 weeks to fully adapt to the change. Corn, soy, and other vegetable oils are commonly used. Although highly digestible, animal fat is not commonly used in horse rations. Horses fed 1 g soy oil/kg/day showed decreased fiber digestibility, so the recommended upper limit, at least for soy oil, is approximately 0.7 g/kg body weight (BW)/day, or approximately 500 mL (2 cups) for a 500-kg (1,100-pound) horse (11).

Horses consuming high-fat diets should also be supplemented with vitamin E to offset the increase in reactive oxygen species associated with fat metabolism. Current understanding of fat in equine diets suggests an upper limit of 0.7g/kg BW/day for soybean oil; however, even diets formulated to be "high fat" for horses contain much less fat than this. Exercising horses adapted to high-fat diets may also spare glycogen during work, potentially delaying the onset of fatigue (11).

Soybean meal is a palatable, high-quality 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 and cottonseed meal should not be used as protein supplements for young, growing horses because of their low lysine content. While these meals can be used in adult horse diets, they will not provide sufficient amino acids and should be supplemented with higher-quality protein sources.

Cane molasses is frequently added to grain mixtures. It is highly palatable, minimizes separation of fine particles, and decreases dustiness of concentrate mixtures. It is also high in potassium, which means it should be avoided in high amounts 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 and/or defluorinated rock phosphate can be used. Dicalcium phosphate is particularly good because the cost per unit of phosphorus is low, the elements are quite available, and it is fairly palatable. Dicalcium phosphate is commonly used in commercial concentrates.