Correction: Last week's article Vet school an expensive but rewarding proposition was mistakenly printed under Dr. Darin Peterson's name. The article was, in fact, authored by Dr. Russ Daly.
Horses require six main classes of nutrients to survive; they include water, fats, carbohydrates, protein, vitamins, and minerals.
Water is the MOST IMPORTANT nutrient; horses can't live long without it!
Energy isn't one of the six nutrients because the horse cannot physically consume energy, however, it is a requirement for sustaining life. The most dense source of energy is fat (almost three times more than carbohydrates or proteins); however, carbohydrates in the forms of fermentable fiber or starch are the most common source. Horses exercising, growing, pregnant in late gestation or early lactation need increased energy in their diet.
Signs of energy deficiency include weight loss, decreased physical activity, milk production, and growth rate. However, feeding a diet too high in energy can cause obesity increasing the risk of colic, laminitis, and contribute to increased sweat loss and exercise intolerance.
Fat 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 grain or carbohydrate source. Fat is normally found at 2 to 6% in most premixed feeds; however, some higher fat feeds will contain 10 to 12% fat.
Carbohydrates are the main energy source used in most feeds. The main building block of carbohydrates is glucose. 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% starch 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. Soybean meal and alfalfa are good sources of protein that can be easily added to the diet. Second and third cutting alfalfa can be 25 to 30% protein and can greatly impact the total dietary protein. Most adult horses only require 8 to 10% protein in the ration; however, higher protein is important for lactating mares and young growing foals.
Signs of protein deficiency include a rough or coarse hair coat, weight loss, and reduced growth, milk production, and performance. Excess protein can result in increased water intake and urination, and increased sweat losses during exercise, which in turn lead to dehydration and electrolyte imbalances.
Vitamins are fat-soluble (vitamin A, D, E, and K), or water-soluble (vitamin C, and B-complex). Horses at maintenance usually have more than adequate amounts of vitamins in their diet if they are receiving fresh green forage and/or premixed rations. Some cases where a horse would need a vitamin supplement include when feeding a high-grain diet, or low-quality hay, if a horse is under stress (traveling, showing, racing, etc.), prolonged strenuous activity, or not eating well (sick, after surgery, etc.).
Minerals are required for maintenance of body structure, fluid balance in cells (electrolytes), nerve conduction, and muscle contraction. Only small amounts of the macro-minerals such as calcium, phosphorus, sodium, potassium, chloride, magnesium, and sulfur are needed daily.
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.
Forages are classified as legumes or grasses. The nutrients in the forage vary greatly with maturity of the grasses, fertilization, management, and environmental conditions. In order to determine the nutrient content in forage it is best to take samples and get them analyzed by a forage testing lab.
Legumes are usually higher in protein, calcium, and energy than grasses. They have more leaves than grasses and require optimal growth conditions to produce the best nutrients. Some legumes include clover and alfalfa. Some commonly used grasses include orchard grass, timothy, bluegrass, and fescue.
Appearance can be a good indicator of the amount of nutrients in the hay, however, color should not be used as sole indicator.
Oats are the most popular grain for horses. Oats have a lower digestible energy value and higher fiber content than most other grains. They are also more palatable and digestible for horses than other grains; however, they can be expensive.
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 it is so energy dense it is easy to over feed corn, causing obesity.
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.
Vegetable oil is the most commonly used fat source in horse feeds. If adding the oil supplement as a top dress to feed start with 1/4 cup/feeding and increase to no
more than 2 cups/day over the course of 2 weeks for the average size horse (1000 lbs.).
Rice bran is a newer fat supplement on the market. It is distributed by some commercial feed dealers. It consists of about 20% crude fat.
When feeding horses remember laminitis. Horses are very sensitive to feed changes, especially carbohydrates like corn. Horses are also notorious for getting out, so always try to keep the feed secure. Use appropriate, consistent measuring devices. Make sure everyone on the property (hired-hands, kids, grandparents, etc.) know appropriate portions. Just wanting to give the horses a treat from cleaning up around the grain bins can be deadly.
Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or firstname.lastname@example.org.