a., b. and possibly c. Vitamins E and A are fat-soluble, which means that a horse who consumes more than he needs can store the excess in his liver and other fatty tissues. Both are also abundant in green, growing grasses but diminish as the plants mature and die. A horse who grazes pasture even for just a few weeks a year will be able to store enough to get through the winter on dried forages. On the other hand, a horse who is fed exclusively on hay or other forms of dried forage year-round may need a supplement with vitamins A and E.
Vitamin E is a potent antioxidant that helps to limit the damage caused by excessive free radicals, electrically unstable molecules that are a byproduct of metabolism. When free radicals are produced in large numbers, such as in the muscles of a working horse, vitamin E helps minimize the oxidative damage to his cells. In addition to horses kept primarily on hay, hardworking athletes, breeding mares and stallions, and horses prone to tying up may benefit from supplemental vitamin E.
Vitamin A combines with compounds in a horse’s retina to play a critical role in night vision, and it is also involved in body functions including reproduction, bone and muscle growth, and regeneration of skin tissue. Horses do not consume vitamin A directly; rather, they consume precursor compounds, primarily beta carotene, that are metabolized into the necessary vitamin compounds in the intestine and liver. Beta carotene is abundant in yellow vegetables, such as carrots, as well as green grass and alfalfa.
Vitamin B1 (thiamine) is necessary for the metabolism of carbohydrates, and it is found in grains as well as fresh and dried forages. However, it degrades with time in stored hays. Thiamine is also produced by microflora in the gastrointestinal tract but not in high enough quantities to meet all of the horse’s needs. Thiamine deficiency is rare in horses, but it can happen, especially in cases where intestinal disease, parasite damage or the consumption of toxic plants, such as bracken fern, interferes with B1 production.
a. Biotin, formerly called vitamin H, aids in the metabolism of fatty acids, proteins and carbohydrates and is essential for the creation of new cells within the body. Biotin is available from several common feedstuffs, including alfalfa and oats, but horses can synthesize all that they need within the gut, and deficiencies have never been reported in horses.
That said, studies have shown that adding a biotin supplement of 10 to 20 milligrams per day to a horse’s diet for at least six to nine months can improve his hoof quality. The effects of biotin supplementation have been confirmed by observing the changes in the structure of hoof wall with an electron microscope, but researchers are not sure exactly how higher levels of biotin in the blood affect hoof growth. (Biotin supplements improve the growth of new horn; it does not affect hoof wall that already exists, so it takes the better part of a year or more for the new, healthier hoof wall to grow in.) Contrary to popular belief, horses with weak, shelly hoof wall are not deficient in biotin---they have about the same concentrations as other horses. Niacin, pantothenic acid
folate and (also known as folic acid) are all B vitamins. Niacin (B3) and pantothenic acid (B5) are both widely available in equine foodstuffs, and both are also manufactured in the gut in sufficient quantities. Each plays an essential role in metabolism.
Folate (B9) plays a role in the formation and growth of new cells. In human medicine, folate deficiencies may result in birth defects, so pregnant women are often given supplements---and so it is often included in supplements for pregnant mares, too. Green grass is rich in folate, however, and the micronutrient is also synthesized in the equine gut, so natural deficiencies in horses are rare.
b. Phosphorus and calcium are the two most abundant minerals in your horse’s body. Calcium makes up about 35 percent of his skeleton, and the mineral also plays critical roles in many functions, such as muscle contraction and regulating the heart rate. Phosphorus is another major component of bone, making
up about 14 to 17 percent of the skeleton, and it also aids the metabolism of nutrients and the utilization of vitamins. Hay and grasses are good sources of both minerals; alfalfa is an especially rich source of calcium.
Horses require both of these minerals in their diet, but it is also important to balance the calcium:phosphorus ratio. That is, the amount of calcium in a horse’s diet needs to at least meet (a 1:1 ratio) or exceed the amount of phosphorus---a ratio of 2:1 is considered ideal, but most adult horses can tolerate higher amounts of calcium. When the ratio is inverted, however, the excess phosphorus inhibits the absorption of calcium, and the horse’s body may begin to pull calcium out of the skeleton for other essential functions. Over time this may weaken his bones and lead to skeletal deformities.
Grains such as corn, barley or oats (1:15 or more) and wheat or rice bran (1:8) contain much higher levels of phosphorus than calcium. If these foods form the bulk of a horse’s diet, over time he may experience serious health issues stemming from a lack of calcium. The occasional bran mash will not hurt a horse, assuming he receives an overall balanced ration, but any abrupt change in diet can lead to gastrointestinal upset. The safest way to feed a mash is to use his regular grain as the base: Simply add enough hot water to soften it.
Copper contributes to bone formation, immunity and the health of elastic connective tissues. Zinc is a component of more than 100 enzymes and plays a role in the metabolism of proteins and carbohydrates. Adult horses usually get an adequate supply of both from a diet based on forages and commercial feeds. Deficiencies and/or imbalances of these minerals play a role in developmental0 orthopedic disease in foals, but commercial feeds formulated for pregnant mares and growing youngsters will offer adequate, balanced amounts of these minerals.
d. In addition to hemoglobin, iron is an essential component of myoglobin, a protein that aids the storage of oxygen in muscle cells, as well as other molecules involved in the transport and storage of oxygen throughout the body.
Adequate amounts of iron are present in most feeds and forages horses eat, and a horse can store iron reserves in his liver, spleen and bone marrow that he can draw upon when needed, so natural deficiencies are rare at any stage of a horse’s life, no matter how hard he works. Deficiencies can occur, though, in horses who have had severe blood loss or extensive parasite damage.
Cobalt is necessary to the synthesis of vitamin B12, which in turn works together with iron and copper to help form new red blood cells. Iodine supports the function of the thyroid gland and plays a role in the synthesis of thyroid hormones that govern metabolism. Manganese plays a role in the metabolism of carbohydrates and fats as well as the formation of cartilage.
All of these minerals are present in feeds and forages, and deficiencies are uncommon. In addition, iodized salt blocks supply horses with needed iodine. Toxicity from overdoses of these minerals are also rare, but consuming extremely high amounts of these elements may interfere with the absorption of other minerals.
b. Sodium and chloride are the two components of table salt. Neither are naturally abundant in a horse’s usual food sources, but horses have a natural appetite for salt and will consume what they need from either a salt block or when offered loose salt. Free access to a source of salt is essential yearround but especially in hotter weather when a horse is losing electrolytes faster through sweat.
Electrolyte supplements can help horses replenish their stores of these minerals and recover faster after sweating heavily. Athletes such as endurance or event horses are obvious candidates for electrolyte supplements when working on hot days, but any horse who sweats extensively for at least an hour or two without an opportunity to eat or drink may also benefit. This may include the weekend warrior after an extended ride as well as the fretful traveler coming off of a trailer. Electrolytes can be administered as a top dressing, an oral gel or paste, or dissolved in water. However you administer electrolytes, always make sure the horse also has access to plenty of clean, fresh water.
c. Selenium works in concert with vitamin E to act as an antioxidant to protect cells from oxidative damage. It also plays a role in the metabolism of thyroid hormones. Selenium deficiencies can cause problems with immunity and reproduction as well as white muscle disease. Horses require only a fairly small amount--typically about 0.1 mg/kg of their ration or about 0.1 parts per million (ppm) of their total diet.
Selenium is naturally occurring in hays and pasture
grasses, but the amount the plants draw up depends on concentrations of the mineral in the soil. Hays grown in certain regions of the country---the Pacific Northwest, the upper Midwest, New England and the East Coast down to Florida---may be low in selenium, so most commercial feed mixes include the mineral in adequate amounts.
However, too much selenium---as little as 3 to 5 ppm---can be toxic, producing signs such as a sparse mane and tail, a dull coat, weak and brittle hooves, neurological issues, and other signs. Soils in some parts of Colorado, Montana, Wyoming and the Dakotas may contain elevated amounts of the mineral. The worst culprits are certain plants called “selenium accumulators,” which contain unusually high amounts. However, these plants tend to be unpalatable, so cases of toxicity tend to be limited to horses in overgrazed pastures who do not have access to enough high-quality forage.
Your veterinarian or local extension agent can advise you about selenium in your region. The other concern is in feeds and supplements. If you’re feeding your horse a selenium-rich hay along with a balanced commercial feed plus multiple supplements, all of which also contain selenium, he may be getting too much. Your veterinarian or an equine nutritionist can advise you on an appropriate feeding regimen for your horse.
Potassium plays a role in regulating the fluid balances in cells as well as muscle function and the transmission in potassium, so deficiencies are rare in horses with a diet based on hays or grasses.
Sulfur is a component of hoof and hair, and it also makes up part of key amino acids, B vitamins, insulin and chondroitin sulfate. Horses are able to get the sulfur they need from plants, and deficiencies are unknown.
Magnesium is an important element found in the skeleton and muscle tissue, and it plays a role in cartilage formation and other functions around the body. It, too, is common in plants and commercial feeds, and deficiency is rare.