Shivers is a fairly uncommon equine condition characterized by tremors and exaggerated flexion of the hind limbs that is most noticeable when the horse is backed or its hind limbs are picked up (for example, for farriery). Often, the horse will also raise its tail head during an episode. The forelimbs are not usually affected, but if they are, the horse will hold its fore leg extended with the hoof just off the ground. Affected horses usually also have muscle loss and weakness.

Shivers is most common in draft breeds, but has also been observed in Quarter Horses, Warmbloods, and rarely in Thoroughbreds. Although it is unproven, shivers is believed to be an inherited trait in draft horses. There is no known effective treatment for shivers and the prognosis for affected horses is guarded because many continue to worsen and may eventually require euthanasia.

The exact cause of shivers remains unknown. Some researchers have speculated that shivers is caused by an abnormal response in the nerves that sense position and tension in muscles and joints. When microscopically examining muscle from horses with shivers, researchers have seen muscle abnormalities similar to those observed with polysaccharide storage myopathy (PSSM). A study of 103 Belgian draft horses at least one year of age found shivers in 18% of the horses examined. Researchers took muscle biopsies from all 103 horses and observed the lesions of PSSM in 36% of horses. Only 6% of horses had both PSSM and shivers. Serum concentrations of selenium and vitamin E were not significantly different between normal horses and horses with shivers or PSSM. There was no statistically significant association between a horse having both PSSM and shivers.

Several researchers have stated that since microscopic changes consistent with PSSM are so common in draft breeds (up to 66% of horses in some studies), that it is difficult to definitively link shivers with PSSM. However, it is possible that some clinical signs of PSSM, such as gait abnormalities, could be interpreted as the horse having shivers.

Muscle biopsy is a useful diagnostic test for horses with shivers to rule out PSSM. If PSSM is present, then dietary change to a higher fat, lower carbohydrate diet may help improve clinical signs in some horses. Most researchers recommend that horses with shivers have supplemental vitamin E and selenium because both have some protective and anti-inflammatory effects for nerves and muscle.

Horses constantly ingest dirt when they graze. Excessive consumption of dirt, especially when pastures become short, sometimes causes potential problems such as sand accumulation in the large intestine. However, the dirt that horses normally consume while grazing supplies some essential nutrients, notably iron. Forages and grains contain additional dietary iron. Young foals can ingest iron when they begin to consume their mare's manure (coprophagy).

Iron is important for hemoglobin, the pigment in red blood cells that allows them to transport oxygen. A deficiency of iron can lead to anemia. Storage and transport proteins account for 20% of the iron in the body. Iron is also found in myoglobin, a muscle pigment, and cyotchromes, enzymes that produce energy for cells. The most common cause of anemia is called anemia of inflammation, which is a normal response of the body to chronic inflammation or infection. The body will sequester its iron stores at its own expense to help fight infection because bacteria also require iron for their metabolism and growth. Other common causes of anemia are chronic blood loss and parasitism.

Researchers in the Netherlands investigated the effects of stall confinement on iron status in foals.1 The study involved three groups of foals: foals kept only in stalls, foals kept in stalls and allowed to exercise 45 minutes per day, and foals kept on pasture. The foals kept in stalls were fed freshly cut grass from the same pasture where the pastured foals were kept.

At 1-3 months of age, the foals kept in stalls became listless and blood work showed that they were anemic and had low blood iron concentrations. All foals were then started on an oral iron supplement. Iron supplementation significantly improved the anemia and serum iron concentration in stalled foals, and they became more active. The authors concluded that soil from the pasture was an important source of iron, since all foals were eating the same grass and only the pasture group had access to soil.

Iron deficiency and iron-deficiency anemia are very rare in horses, especially in grazing animals. Anemia can be caused by a wide variety of illnesses, drugs, and other nutrient deficiencies. The diagnosis of iron deficiency can be more difficult that it seems because of the effects of any concurrent illness and unreliable serum iron concentrations. Measurement of blood transferrin, an iron transport and storage protein, is more reliable to diagnose iron deficiency. If the horse has access to pasture, iron deficiency is unlikely. 

Excessive iron supplementation in horses, especially foals, can be dangerous and lead to liver failure. Most anemic animals are anemic for reasons other than iron deficiency, especially if they have access to pasture. Iron supplements should only be given for conditions known to respond to supplemental iron, and the manufacturer's recommendations should be followed to avoid possible toxicity.

Brommer, H., and M.M. Sloet van Oldruitenborgh-Oosterbaan. 2001. Iron deficiency in stabled Dutch warmblood foals. Journal of Veterinary Internal Medicine 15:482-485.

Q: I own nine horses, and three of them are older. Most of my horses are on grass during the summer with mineral and salt blocks, and they have access to a loose mineral product.  The old horses are fed a coffee can of pelleted wheat midds and wet beet pulp twice each day.

 In the fall and winter, I add about a half pound per feeding of rice bran. When grass season is gone, the horses are fed either round bales of prairie hay or square bales of prairie brome mix. The younger horses (6 to 14 years old) get about two pounds of wheat midds per day plus hay and minerals. I don't feed a lot of grain and generally no grain in the summer. Most of the horse are very easy keepers, with two being borderline metabolic cases. Is it OK to feed the wheat midds as grain? Do I need to top-dress with anything? We buy the wheat midds bulk for the cattle, so they are less expensive than grain manufactured specifically for horses.

Would wheat midds make a horse high-strung?  We purchased one of the older horses (a 27-year-old gelding) with hopes it would be a safe first horse for my son. We feed him more than the previous owner, and he also gets a daily joint supplement. Now this gelding has more energy than we really wanted.

Am I providing my horses with proper nutrition?

A: The only risk you have with the diets you describe is a reversed calcium-to-phosphorus ratio. Whether or not you have a calcium problem depends on the amount of calcium in your forages and the amount of wheat midds you are feeding. If you are adding rice bran that is not stabilized or has added calcium, it may be compounding the problem. During the summer when the horses are on pasture and not getting any wheat midds or rice bran, you do not need to add anything.  However, when you start feeding wheat midds you should add a little limestone to the feed. My estimation is that for every pound of wheat midds or rice bran a minimum of 10 grams of limestone is needed, but this will also be dependent on the amount of calcium in the forage.

Using MicroSteed, ration evaluation software from Kentucky Equine Research (KER), I compared the old-horse winter diet with KER's nutrient and energy requirements. Because the calcium-to-phosphorus ratio was below 1, and ideally it should be between 1 and 2, I added limestone. 

Yes, wheat midds can make a horse high-strung. Wheat midds are energy-dense (around 3 Mcal/kg), which is much higher than forage (1.5-2.2 Mcal/kg). The form of the energy is most relevant here, as wheat midds are much higher in starch (around 25%) than hay (>5%). The horse probably feels better because he has more energy and perhaps his joints ache less, so his true colors are showing. If this horse can maintain his weight on forage (plus salt and minerals), he will probably become more cooperative as a beginner's horse. If not, the rice bran may be a better choice for energy than the wheat midds because it is higher in fat, which has been shown to add calories but not make horses excitable.--Kathleen Crandell, Ph.D.

Grass, hay, and grain go in one end of the horse and what's left comes out the other...what more does anyone need to know about the digestive tract? For owners who want to keep their horses healthy, the answer is, "Plenty!"

Horses are herbivores, or plant eaters. Unlike cattle and many other cud-chewing herbivores, horses are not ruminants. The horse's digestive system is made up of the foregut (stomach and small intestine) and the hindgut (cecum and colon). Each part has an important function, and each can also be the site of problems ranging from the slightly troublesome to the deadly serious. An understanding of the structure and function of each section of the system can help horse owners keep their equine charges free of digestive upsets.

MOUTH Digestion begins in the mouth as horses chew their feed, grinding it into smaller pieces and moistening it with saliva. Amylase, an enzyme in the saliva, begins the process of breaking down carbohydrates. Saliva also helps food travel smoothly through the esophagus, the four-foot-long tube leading to the horse's stomach. Food that is too dry may stick in the esophagus, contributing to a condition called choke. While not the same as choking in humans, this is still a serious situation that might require veterinary treatment.

What owners can do: To be sure the horse can chew properly, schedule dental checkups once or twice a year to smooth any jagged edges and make sure the horse's teeth are properly aligned. Owners of choke prone horses can soak feeds, or add water to grain and hay before feeding. All horses should have a constant supply of clean water.

STOMACH Swallowed food moves down the esophagus to the stomach, a relatively small organ with a capacity of only two to four gallons. The organ's limited size is well suited to processing a continuous supply of food, such as when the horse is grazing or picking through hay. A large grain meal, however, may overfill the stomach, causing distention, discomfort, and signs of colic. Long periods with nothing to eat can also cause problems because the stomach continues to secrete gastric acid even when it is empty. Without the buffering function of saliva, which is produced only while the horse is chewing, digestive fluids can cause ulceration of stomach tissues. Although there is little absorption of nutrients at this location, digestion of protein begins in the stomach through the action of pepsin and hydrochloric acid. The stomach also regulates the rate at which feed passes into the small intestine.

What owners can do: Stay close to a natural feeding pattern by allowing the horse to graze or eat hay as continuously as possible. Rather than offering one large meal, split daily grain rations into two or more small feedings of less than five pounds each.

SMALL INTESTINE This tube-like organ can reach 70 feet in length, and food usually takes from one to eight hours to pass from one end to the other. Various digestive enzymes break down protein, fat, and carbohydrates, allowing nutrients to be absorbed by the blood. The makeup of this enzyme mixture changes in response to dietary modifications, with several days required to make the adjustment. Sudden variations in the type or amount of feed can result in less than optimum feed breakdown, keeping the horse from getting the maximum benefit from what has been eaten. Ideally, most of the starch portion of the diet is digested in the small intestine, leaving very little except fiber to pass into the large intestine. If the horse has eaten an extremely large grain meal or a great quantity of fresh grass, the digestive ability of the small intestine may be overwhelmed, resulting in a significant amount of starch being passed to the large intestine. Problems in the small intestine include hypermotility (spasmodiccolic); twisted sections that cut off circulation and passage of food; and intussusception, a condition in which part of the intestine becomes telescoped upon itself.

What owners can do: Feed small grain meals of no more than five pounds. Monitor consumption of fresh grass, especially for animals that are being turned out to pasture after long periods of stalling. Introduce new feeds gradually by mixing a handful of the new ingredient into regular feed and increasing by small quantities at each successive meal until the full amount is given. Make changes in hay or forage the same way. This method allows the intestine to adapt slowly to the modified diet, a process that should take about 7 to 10 days.

CECUM Bacteria, protozoa, and fungi in the cecum aid in the fermentation of dietary fiber, producing volatile fatty acids, an important source of energy. The process also gives off enough heat to keep the horse comfortably warm in chilly weather. Cecal microbes synthesize vitamin K and the complex of B vitamins. Excess starch that is not digested in the small intestine accelerates cecal fermentation. This causes overproduction of gas and lactic acid, and severe abdominal discomfort may follow. Changes in pH disturb the microbial balance within the cecum, leading to the production and absorption of toxins, and the result is often laminitis.

What owners can do: Make every effort to avoid upsetting the balance of microorganisms in the hindgut. Any change--moldy feed or hay, schedule variations, travel, stress, deworming, illness, use of antibiotics--can be a threat to digestive health, so these changes should be minimized or made slowly so that the organs of digestion have a chance to adapt. A course of probiotics, preparations designed to keep the microbial population of the cecum vigorous, may be given during stressful times. A veterinarian can advise on the use of probiotics.

COLON Mainly a site of fluid absorption, the colon can also be a source of colic pain if material stops moving freely. The colon makes two tight folds or turns where its contents sometimes become impacted, leading to a buildup of gas and possibly twisting. Food moves slowly through the hindgut, completing the transit in about two days. Under normal circumstances, indigestible portions of the feed are passed from the body as manure.

What owners can do: Build the horse's ration around high-quality roughage, adding concentrated feeds only as needed to meet the demands of reproduction, growth, or performance. Provide a constant supply of water. Follow a regular schedule of deworming, dental care, and exercise. Careful management will go a long way toward avoiding digestive problems.

Navicular syndrome (or navicular disease, or caudal heel pain syndrome) is a degenerative condition of structures in the horse's heel. The navicular bone lies at the back of the heel, and the deep digital flexor tendon runs down the leg and wraps under the navicular bone before anchoring to the coffin bone. Pain results from changes in the bones, bursa (fluid-filled joint structures designed to absorb shock and reduce friction), tendons, and ligaments in this area.

What signs does an affected horse show?

Lameness is the classic sign of navicular syndrome. This can appear suddenly, but a more common pattern is mild lameness that becomes progressively worse over time. A horse with navicular syndrome feels pain in the heels of the front feet, and its movements reflect attempts to keep pressure off this area. At rest, the more painful foot is often "pointed," or held slightly in front of the other forefoot, thus bearing little or no weight. Because the horse tries to impact the ground flat-footed or toe-first instead of the more normal heel-first pattern, the gaits are short-strided and stiff. A horse with navicular syndrome has difficulty turning sharply, going downhill, and moving on rocky or hard ground. Picking up one front foot for trimming or shoeing is painful because weight is concentrated on the other foreleg, and affected animals may become quite uncooperative during farrier visits.

Does navicular syndrome affect all types of horses?

While there's no guarantee that a particular horse will or will not develop navicular trouble, the problem is most common in stock-type horses (Quarter Horses, Paints, Appaloosas). There is a fairly high incidence in Thoroughbreds and some warmblood breeds. Arabians, on the other hand, are rarely affected. Lameness from navicular syndrome is most often diagnosed in horses between the ages of seven and fourteen.

What causes this condition?

No one knows precisely what causes navicular syndrome. Like some other lamenesses, a combination of factors is probably to blame. Conformation seems to be important, with more cases occurring in horses with heavy bodies, upright pasterns, and small hooves. A large number of affected horses have a history of work involving front-leg impact (jumping, cutting, roping, and reining) or increased concussion (parade work or other use involving hard or rocky surfaces). Suspicion has also been directed at irregular farrier care, unbalanced hooves, and shoeing practices that reduce contact between the frog and the ground. A common thread seems to be the combination of increased stress and limited oxygenation of structures in the heel area, but the exact cause of tissue damage and inflammation has not yet been determined.

How is the diagnosis made?

Heel pain is not always caused by navicular disease: temporary lameness from bone fractures, muscle strains, and trauma to tendons or ligaments can mimic the syndrome. A vet may need to use a combination of flexion tests, hoof and frog pressure tests, nerve blocks, X-rays, scintigraphy, thermography, ultrasound, venograms, and magnetic resonance imaging (MRI) to determine the cause of the horse's discomfort. Diagnosis is made after a consideration of the horse's history, use, conformation, and test results.

At one time the appearance of lollipop-shaped invaginations (holes) in the navicular bone on X-rays was considered to be definitive evidence of navicular syndrome. However, it has been found that not all horses with such invaginations exhibit clinical signs of lameness, and some acutely lame horses fail to show any trace of bone abnormality. Interestingly, research at the Idaho Museum of Natural History found lollipops in 17% of navicular bones recovered from equine skeletons up to three million years old, showing that the phenomenon is not of strictly modern origin. In the "history repeats itself" category, bones from large-bodied horses were more likely to show invaginations, and animals living in areas of hard and rocky terrain were also more often affected than grassland-dwelling animals.

Can navicular syndrome be cured?

Consultations with a veterinarian and a farrier are the first steps in combating navicular syndrome. While there is no cure, a prompt diagnosis allows treatment-farrier, medical, or surgical-to begin early in the course of the disease. Proper trimming and therapeutic shoeing can provide pain relief for many horses. Farrier care is aimed at correcting broken-back or broken-forward pastern angles and normalizing underrun or contracted heels. Generally a shortened toe, either through trimming or shoe design, is a goal. Heel support afforded by egg bar or wide-web shoes reduces pain in some horses, and a shock-absorbing polyurethane shoe from Switzerland is being tested as a possible therapeutic aid. Overall, proper trimming and shoeing can relieve discomfort in about 30% of horses with navicular syndrome.

Polysulfated glycosaminoglycans and hyaluronic acid sometimes lead to improvement, possibly by inhibiting enzymes involved in tissue breakdown. Anti-inflammatory medications can be injected into the heel area or given orally for pain relief. Medical treatment combined with therapeutic shoeing can help about 60% of affected horses.

Palmar digital neurectomy, a surgical procedure to sever the nerves to the painful area, is a last resort in treating navicular syndrome. This option eliminates sensation in the rear third of the foot, thus ending pain and lameness, but it is not a permanent cure. Degenerative changes continue to occur within the hoof, and about one-third of treated horses are lame again within two years.

Can feeding practices help to prevent or treat navicular syndrome?

Navicular syndrome is not directly caused by feeding practices, but as with any condition affecting the legs and feet, an overweight horse puts excessive strain on its musculoskeletal system. With the strong correlation between heavy-bodied, small-footed horses and navicular syndrome, common sense should warn owners not to allow their horses to become too fat.

Pasture intake can be limited by muzzling or dry-lotting horses, and easy-keeping animals can be fed a low-calorie supplement pellet such as All-Phase, thus providing essential vitamins and minerals without an overabundance of calories. Increasing exercise is also beneficial for keeping horses in trim condition. Although turnout and light exercise are preferred to stall rest for navicular horses, heavy work is usually ruled out as a conditioning measure for these animals. Keeping a horse at a mid-range body weight may delay the onset of navicular syndrome in susceptible individuals, and can also help to keep affected animals more comfortable.

The endurance horse is unique among all other equine athletes. Because of the prolonged demands placed upon the endurance horse with protracted moderate intensity exertion, its performance may be influenced quickly by the quality of its diet. A simple diet of hay and oats may lack essential nutrients that allow the horse to perform as expected. Understanding how competition affects the nutrient needs of the horse will help the owner select the appropriate supplementation program for the individual endurance horse.

Improving the diet
Approximately 80 to 90% of the feed eaten by horses is used to satisfy their energy requirements. Horses, like people, utilize energy to run most of the chemical reactions within the body, particularly to fuel muscle contractions vital to the work effort. As such, any horse diet should focus on providing adequate energy (calories). The major source of that energy is dietary carbohydrates (grass, hay, grain, molasses, etc.) Because the amount of energy available from forage alone can be a limiting factor for performance, grain is often added to increase the energy density of a diet.

Dietary fat is another source of energy readily employed by the horse for calories. Fat contains roughly 2.25 as much energy as an equal weight of carbohydrate, so less is needed to fuel body processes. Dietary fat has been scientifically proven to be advantageous to the performance of horses undergoing prolonged bouts of exercise.

During long duration, moderate intensity exercise, the body depends on fat stores to supply energy for work. The addition of fat to the diet has been found to increase the ability of the horse to mobilize fat stores for energy, sparing the muscle glycogen (sugar) stores for more intense bouts of exercise. In a study done at Kentucky Equine Research comparing differences in fat utilization between breeds, it was found that Arabians (the most common breed used for endurance) are much more efficient at mobilizing and burning fat as an energy source than are Thoroughbreds.

There are different dietary fat sources available to the horse, and the most common are vegetable oils. Vegetable oils can be fed safely up to 15% of the total diet. Another source of fat is rice bran, the heat-stabilized outer layer of the rice kernel which contains 20% fat. Compared to oats, rice bran can contain 120% of the digestible energy on a pound for pound basis. Therefore, this source of fat is beneficial in adding calories to the diet without increasing the amount of grain being fed.

The remaining 10 to 20% of the diet is used to satisfy the nutrient requirements that drive the cellular processes inside the body. Protein is the major nutrient the body needs to support normal body functions. Vitamins and minerals play a vital role in metabolism but are needed in relatively small amounts. A simple diet of hay and oats may lack some of these key nutrients. Grain concentrates are designed to complement the nutrient profile of forages but must be fed at the recommended level in order to obtain balanced nutrition. For many endurance horses of Arabian descent, the recommended feeding rate of commercial grain mixes provides too many calories, resulting in excess weight gain.

A horse that eats less than the recommended amount may be short on the supplemental protein, vitamins, and minerals that are added to complement the deficiencies in forages. A specialized grain mixture designed for endurance horses is preferable. Failing that, a specially designed concentrate containing essential proteins, vitamins, and minerals can be used to top off a feed that is provided at a lower rate than recommended. If protein is sufficient in forage and grain, then adding a well-balanced vitamin and mineral supplement will be sufficient to fill in the shortcomings of the diet.

Supplements
Hooves: Horses often have unique requirements for certain nutrients to help improve performance. This is especially true of endurance horses. For instance, not every horse is blessed with hard, resilient hoof walls. The hooves of endurance horses often take a beating from the long hours on the trail. Research has shown that some horses with weak hooves benefit from supplementation of certain nutrients. Specific additives like biotin, methionine, iodine, and zinc, or a combination of them, can be added to the horse's diet to improve hoof quality.
Muscles: Endurance competitions can also be hard on the horse's muscles, which are in constant use during the hours of training necessary to compete successfully. During muscular exertion, free radicals (waste products of oxygen metabolism that can damage cell components) are produced and can cause muscular damage if not eliminated.

Certain nutrients, specifically vitamins C and E and selenium, are key antioxidants responsible for quenching free radicals found to build up in muscle tissue. These nutrients work in concert to reduce muscular soreness and stiffness associated with exercise. Magnesium is necessary for proper nerve and muscle function and may be insufficient in the diet of some hard-working horses.

Immune function
Antioxidants are also important for support of the immune system. Human endurance athletes may have reduced immune function for about 70 hours following a bout of prolonged and intensive exercise. During this period the body may be particularly susceptible to infection, allowing viruses and bacteria to gain a foothold. Lack of sleep, severe mental stress, malnutrition, weight loss, or other stressors commonly associated with shipping and competing can also exacerbate depression of immune function. Although the research has been done in humans, it may very likely be similar for the equine endurance athlete. Whether human or equine, body cells need specific nutrients to be able to properly divide and produce necessary antibodies. Many enzymes in immune cells require the presence of micronutrients, and critical roles have been defined for zinc, iron, copper, selenium, and vitamins A, B6, C, and E.

Electrolyte losses
Electrolytes are ions (charged particles) found inside and outside of cells in the body. Electrolytes play an important role in maintaining osmotic pressure, fluid balance, and nerve and muscle activity. A horse sweats in order to get rid of excessive heat that has built up in the muscles. Horse sweat consists of water and a high concentration of electrolytes. Any level of work produces body heat and subsequent sweating. When an endurance horse sweats, it loses essential electrolytes (particularly sodium, chloride, and potassium) that are necessary for top performance. Other factors may cause a horse to sweat, such as the time the horse spends in or tied to a trailer during the heat of the day or the stress of an unfamiliar environment.

Excessive sweating with subsequent loss of electrolytes can cause fatigue and muscular weakness. Usually, a horse can replenish lost electrolytes from its normal diet. However, under extended work or stressful circumstances, the electrolytes that are lost in sweat cannot be replaced from the daily ration of grain and forage.

The amount of sweat produced by an endurance horse during a competition far exceeds that of any other sport horse. It may be difficult to realize the volume of fluid lost as the sweat may evaporate before it is even seen. Because electrolyte balance is critical for maximal performance, replacement of lost electrolytes is imperative. During long rides, calcium and magnesium may be also be lost in sweat in amounts high enough to cause metabolic disorders. Specific electrolyte supplementation can be provided to the horse during the competition phase, but it may also be necessary to provide a daily dose for horses that are in training for endurance events. Free choice water should always be available to the horse when electrolytes are used.

Stomach problems
The rigors and routines of training often interrupt the natural grazing behavior of performance horses, and consequently their stomach acid buffering mechanism.

Indigestion often results. If a horse has any of the following signs it may be suffering from heartburn: drop in performance, sour attitude, poor hair coat, grinding teeth, inappetance, and weight loss. Many endurance horses enjoy the luxury of having 24-hour turnout on pasture, which is ideal for the prevention of ulcers or heartburn.

However, when this lifestyle is interrupted and the horse is loaded on a trailer, put in a stressful situation, fed differently than normal, and then asked to compete for hours with limited meals, he may end up with a sour stomach that will affect performance or attitude. Medications designed to alleviate these discomforts or those specifically designed to be stomach buffers can help horses with these problems.

Chromium supplementation
Strenuous exercise and high-grain diets increase the excretion of chromium in the urine of equine athletes, thereby depleting the natural reserve of this mineral in the body. Chromium is an integral component of glucose tolerance factor, which is thought to potentiate the action of insulin in chromium-deficient tissue. In a Kentucky Equine Research trial, chromium-supplemented horses showed lower insulin levels in response to a meal, and maintained lower insulin levels throughout a standardized exercise test. This means that with chromium supplementation less insulin is required to assimilate and utilize the same amount of glucose from a meal.

Another significant result was that peak levels of lactic acid were lower when the horses received supplemental chromium. Since lactic acid accumulation contributes to fatigue during exercise, this can be interpreted as being beneficial for the performance horse. For the endurance horse that has a low tolerance to additional grain in the diet, a chromium supplement may be advantageous. Chromium supplementation may also help reduce the incidence of tying-up in certain horses. One of the possible causes of tying-up is related to carbohydrate metabolism, and therefore chromium's action on glucose and insulin may be beneficial in this situation.

Keeping an endurance horse fit and healthy involves more than just putting in a large number of miles on trails. The work required of these horses is quite different than that of any other equine athlete. The challenge is to provide the correct combination of nutrients that will support the special needs of these athletes during both training and competition.

A superbly conditioned horse that can fully utilize its athletic talent in top-level competition, recovering quickly without muscle damage after strenuous exercise...that's the dream of many  horse owners. A superior nutritional plan is one key to turning that dream into reality, and natural vitamin E is one of the crucial elements in the equine athlete's dietary regimen. Whether a horse's work involves racing, eventing, endurance, trail riding, or reproduction, vitamin E plays a huge role in both overall health and specific performance.

Vitamin E is abundant in fresh grass, so all horses get plenty every day, right? Well, yes, except when they're kept in a stall for many hours...or when they don't have access to pasture...or when grass is scarce or dormant...or when they eat mostly hay, which contains lower levels of this important dietary element...or when they're exercising intensely, in which case their requirement for antioxidants increases dramatically. As horse owners learn more about equine nutrition, they begin to see that their horses may need supplementation with a natural form of vitamin E.

Recognized as a unique nutrient less than a hundred years ago, vitamin E has many important functions in various body systems. In reproduction, vitamin E supplementation may positively influence fertility in broodmares. In addition, mares supplemented with vitamin E may demonstrate increased passive transfer of antibodies to foals. In a University of Connecticut study, supplemented mares showed higher antibody concentrations in blood and colostrum, and their foals also had correspondingly higher levels of antibodies than the foals of unsupplemented mares. Because a very young foal's resistance to disease depends entirely on antibodies received from its dam, this immune system support is essential to foal health in the first months of life.

Although young animals begin to produce their own antibodies as they develop, horses never outgrow their need for vitamin E. For mature horses in a schedule of training and performance, vitamin E's role as an antioxidant is important in protecting tissues and cells from degradation by free radicals. These products of oxidation can cause irreparable damage to cell membranes throughout the horse's body. A horse without sufficient stores of vitamin E often experiences muscle stiffness and soreness after intense exercise. A prolonged recovery period often necessitates a slowdown in the training schedule.

Even idle horses need a steady supply of vitamin E for routine tissue maintenance and healthy immune status. Horses grazing fresh pasture usually take in enough of this vital nutrient to meet day-to-day requirements, but vitamin E is quickly lost as forage becomes dormant or is dried and stored as hay. Stall-kept horses without daily access to green grass benefit from vitamin E supplementation, as do many horses during the winter months when grazing is limited or nonexistent. As research has revealed the need for a steady supply of this important vitamin, equine nutritionists have worked to discover the best way to deliver vitamin E in a stable, digestible form. In order to understand the difficulty of this seemingly simple task, it is necessary first to realize that the term "vitamin E" actually refers to a family of substances. Among these, only two--alpha-tocopherol and gamma-tocopherol--possess the potent antioxidant properties that make the nutrient so important to the equine diet. Alpha-tocopherol is the most biologically active, and is the form found most abundantly in the horse's body.

Commercial supplies of natural alpha-tocopherol (d-alpha-tocopherol) are limited, making it an expensive component of animal feeds. In addition, the substance is unstable unless it is processed into a form known as d-alpha-tocopherol acetate, a step that protects against chemical changes as the feed is manufactured and stored. Efforts to synthesize a stable, inexpensive alpha-tocopherol have resulted in a compound of eight different molecules, only one of which is structurally similar to the natural form. This synthetic vitamin E is known as dl-alpha-tocopherol.

As with many other nutrients, the different forms of natural and synthetic vitamin E have quite dissimilar properties that make some more useful than others. Supplementation with synthetic vitamin E (dl-alphatocopherol acetate) is the least effective in elevating plasma tocopherol levels in horses. However, primarily because of its lower cost, synthetic vitamin E is frequently added to equine feeds, even though it offers quite limited bioavailability to the horse. Such feeds can legally claim to contain vitamin E, and well-meaning owners who purchase these feeds may be mistaken about providing adequate supplementation unless they read feed product labels to differentiate between vitamin E forms.

In a recent study conducted at Kentucky Equine Research, vitamin E plasma levels were measured in eight Thoroughbreds. All horses received the same diet and either 1,000 mg/day of synthetic vitamin (four horses) or 1,000 mg/day of the natural-source vitamin E. The results revealed that an equivalent amount of the natural-source vitamin E increased plasma vitamin E levels 56% above baseline compared to the synthetic product.

Certain supplements provide superior antioxidant support to horses that require vitamin E supplementation. Horses that might benefit from supplementation include those without access to fresh forages such as pasture, performance horses in strenuous work, breeding horses, and those diagnosed with neurological problems such as equine motor neuron disease (EMND) and equine protozoal myeloencephalitis (EPM).

Proper nutritional management of the breeding stallion is paramount. Breeding stallions are often the most frustrating horses on a farm to maintain at optimal body condition; some become too lean at the height of breeding season, while others remain candidates for Weight Watchers no matter the season. By providing a carefully balanced diet and monitoring weight regularly, a stallion's waistline can be kept trim and tidy all year long.

For the stallion, the year can be divided into two basic phases, breeding season and the off-season. The breeding season lasts approximately five months for the majority of stallions. In the Northern Hemisphere, the breeding season commences in mid-February and ends on July 4, though these dates are not necessarily concrete. Tennessee Walking Horse breeders, for instance, often breed mares so they foal in the autumn. In the Southern Hemisphere, the schedule is flip-flopped, with the breeding season beginning the first of August and winding up in late January. Some stallions pull double duty, servicing a book of mares in the Northern Hemisphere early in the year and a separate group in the Southern Hemisphere later in the year. It's not unusual for these stallions to breed more than 300 mares annually.

In 2001, one popular Thoroughbred stallion bred 216 mares in the United States and 155 in
Australia. Regardless of the number of mares bred, stallions must be properly nourished to perform their jobs successfully.

From a nutritional standpoint, the act of breeding can loosely be classified as work. According to Nutrient Requirements of Horses, produced by the National Research Council, breeding stallions expend nearly the same amount of energy as performance horses in light work. This may be slightly elevated when stallions are bred multiple times a day. Several large studs in Kentucky, for example, breed their charges three times daily during the peak breeding season. Stallions also vary greatly in the amount of exercise they give themselves; some are naturally more sedentary than others. During breeding season, nervous stallions may burn valuable calories fence walking, stall circling, pacing, and weaving.

Breeding may not be the only work certain stallions perform. Some continue to be ridden and trained while performing stud duties. In these instances, energy requirements would be higher still. The breeding stallion requires, above all else, a balanced diet. First and foremost, stallions should be provided with high-quality forage, consuming approximately 1.5-2 pounds of hay per 100 pounds of body weight. A 1,200-pound stallion should therefore be offered 18-24 pounds of hay daily. The minimum amount of hay offered should be 1% of body weight. Depending upon the time of year, good quality pasture may supply some or all of the stallion's forage needs.

During the breeding season, the addition of energy-dense feeds, usually grains may be necessary to satisfy calorie requirements for the increased workload of breeding. No more than 0.75 pounds of grain per 100 pounds of body weight should be fed to a stallion per day, and no single meal should weigh more than five pounds. If grain is fed, the amount of hay given may be decreased slightly. Fortified concentrates will contain the vitamins and minerals stallions necessary for optimal nutrition. As with all horses, stallions should have access to a white salt block or a trace-mineralized salt block.

If the stallion is consuming a well-balanced diet, the addition of other vitamins and minerals will not enhance fertility. Although much information has been bandied about through the years, there is no scientific evidence to suggest that vitamin C and E supplements or zinc additives boost reproductive performance. As breeding season approaches, stallions should be in moderate to fleshy body condition, which means the stallion's ribs should be palpable but not visible and minimal fat may be deposited along the withers, behind the shoulder, and around the tailhead. Once an ideal weight has been achieved, every attempt should be made to keep the stallion's weight static. This is best achieved by weighing the horse periodically, usually weekly or biweekly. A weight tape or portable scales can also help track weight.

An extremely thin stallion may not have the energy stores necessary to carry on through an arduous breeding season without his performance suffering. Stallions become too thin when they expend more calories than they consume. To encourage weight gain, provide free-choice access to high-quality forage (usually in the form of pasture and/or grass hay) and supplement with the recommended amount of a fortified concentrate. If a stallion fails to gain weight on this basic diet, a fat supplement such as rice bran or vegetable oil can be included in the ration. Because of the energy density of these supplements, stallions will be consuming far more calories than it is possible to obtain from feeding safe amounts of common feedstuffs. One benefit of a fat-enriched diet is a glossy coat, which will enhance the stallion's appearance.

Another fairly common reason for thinness among breeding stallions is reduced appetite. The anxiety surrounding the breeding shed may prevent some stallions from polishing off meals. If this is the case, every effort should be made to make meals especially palatable. The use of molasses and other appetizing feedstuffs will typically encourage an otherwise distracted stallion to eat. If necessary, remove any supplements (e.g., rice bran or vegetable oil) that may be playing a role in his inappetance.

More common than underfeeding, however, is overfeeding. Obesity predisposes stallions to laminitis, soundness problems (particularly of the hind legs, which is reflective of the strain placed on them during breeding), and possibly fatal aortic rupture.

Extremely overweight stallions are also thought to have lowered libido. If obesity is a problem, stallions should have restricted access to pastures, especially in the spring, and only enough grain to ensure the stallion's vitamin and mineral requirements are being met. An alternate way to satisfy these requirements is to feed a multipurpose vitamin and mineral supplement.

During the off-season, stallions may be maintained on high-quality forage alone, particularly if they are easy keepers. If a stallion requires concentrate, feed only enough to maintain optimal body weight, being sure not to overfeed.

Every endurance competitor appreciates that electrolytes are a critical component of a horse's nutritional program. Electrolytes are mineral salts that play an important role in maintaining osmotic pressure, fluid balance, and nerve and muscle activity.

During endurance exercise, sodium (Na+), chloride (Cl-), and potassium (K+) are lost in large quantities through sweating. Loss of these electrolytes causes fatigue and muscle weakness, and decreases the thirst response to dehydration. It is vitally important that endurance horses begin competition with optimal levels of fluids and electrolytes in their bodies and that these important nutrients are replaced throughout a ride.

Sweat Losses
It is important to have some idea of the magnitude of electrolyte loss a horse incurs during exercise before a feeding program can be developed to replace these losses. Because most electrolyte losses in the horse occur through sweating, one method of calculating electrolyte requirements can be based on different amounts of sweat loss. Table 1 contains the levels of Na+, Cl-, and K+ required per day by a horse at rest and after exercising hard enough to lose 5, 10, 20, or 40 liters of sweat.

The amount of sweat loss will depend on a number of factors such as duration and intensity of exercise, temperature, and humidity. In general, horses exercising at low intensity (12-18 km/hr) will lose between 5 and 10 liters of sweat per hour. During high-intensity exercise (30-35 km/hr), sweat loss levels reach as high as 15 liters per hour. At the 1996 Olympic Games in Atlanta, horses lost an average of 18.4 kg of body weight during the speed and endurance phase (day 2) of the three-day event, and this translates to a sweat loss of around 15 liters.

Electrolyte Requirements during Training
Daily electrolyte requirements can be estimated by calculating the total amount of mileage logged weekly by the horse, taking into account the environmental conditions under which the training occurs. For example, if an endurance horse was logging 50 km of work per week in a cool dry environment, it would require only about 60-120 grams (2-4 ounces) of a well-formulated electrolyte supplement to meet its daily electrolyte requirements.

The lower level of supplementation would be adequate if the horse was also receiving adequate forage and a grain mix that contained supplemental salt, as well as access to a salt block. Horses at rest will normally consume around 50 grams of salt per day from a salt lick. As training mileage and environmental temperature increase, so does the requirement for electrolyte supplementation. Horses that are training heavily (100 km/week) in a hot environment may need 140-200 grams (5-7 ounces) of supplemental electrolytes.

Recommendations are based on supplementing electrolytes at the same rate daily even though the amount of exercise performed each day will vary. This is probably a reasonable approach to supplementation except for days when the training distance is especially long. For those days, additional supplementation may be warranted. As a rule of thumb, 60 grams (2 ounces) of electrolyte supplementation are required for each hour of exercise in cool climates. This rate of supplementation will double in hot environments when sweat loss is extensive. A long training ride of 60 km (~4 hours) in moderate temperatures would therefore produce enough sweat loss to require 240 grams (8 ounces) of electrolyte supplementation.

This level of supplementation would need to be partially replaced during the ride (60 grams at 20 and 40 km) using an oral electrolyte paste with the remainder of the electrolyte administered after the ride. If the horse will not consume this quantity of electrolyte (120 grams or 4 ounces) in a single meal, then 60 grams can be administered as a paste at the end of the ride. When administering oral electrolyte pastes, it is absolutely essential that the horse have access to water. If the horse refuses to drink, do not administer an electrolyte paste.

Supplementation during Competition
There is a great deal of controversy about how to administer electrolytes during competition. A number of different strategies have been used successfully by competitors, and the recommendations that will be given here are not necessarily the only way to achieve success. During competition, sweat losses can be very large.

How much water and electrolytes does an endurance horse lose during a competitive ride? Using the sweating rates described earlier, an endurance horse will lose between 45 and 60 liters of sweat during a 160-km ride. This represents electrolyte losses of 460-690 grams. Additionally, 9-14 grams of calcium and 5-8 grams of magnesium will be lost through sweating. It is debatable whether all of the losses can or need to be completely replaced during the competition. Research has shown that endurance horses participating in 80- to 160-km events often have a fluid deficit of 20 to 40 liters despite having access to water and electrolytes during the ride.

Canadian researchers have shown, however, that endurance horses with less pronounced fluid and electrolyte alterations during a competitive ride were more successful than those with greater changes. Therefore, it is absolutely essential that a large proportion of the electrolytes and water lost in sweat be replaced during the ride.

Pre-ride electrolyte loading
The endurance horse must start the competition with adequate stores of both water and electrolytes. This can be accomplished in two ways. First, the endurance horse should be on a high level of forage (hay or pasture) intake before a ride. When a horse is fed liberal quantities of forage, it can store extra water and electrolytes in its large intestine. These stores can be called on to replace sweat losses early in the ride. Second, extra electrolytes can be administered the night before and the morning of the ride.

The horse's system is finely tuned to balance the amount of electrolytes and water that it stores in its body at rest, so excessive pre-ride electrolyte supplementation should be avoided. Moderate supplementation (60 grams the night before and 60 grams the morning of competition) will insure that the horse has adequate electrolytes within its body and will provide additional electrolyte stores within the gastrointestinal tract.

Electrolyte supplementation during competition
Electrolytes should be supplemented throughout competition. The type of electrolyte supplement used during competition is slightly different than that which is used during training. This electrolyte should provide additional calcium and magnesium along with sodium, chloride, and potassium. If calcium and magnesium losses are not replaced by mobilization of skeletal stores or by supplementation, metabolic disturbances such as thumps may occur. Electrolytes should be administered to horses at each vet check and at water stops along the trail. The best way to administer electrolytes is in the form of a paste.

Pastes are commercially available, or they can be made up fresh at the vet check by diluting an electrolyte powder in applesauce, water, or liquid antacid. A reasonable dose of electrolyte powder (or equivalent) is 60 grams at each vet check. Thirty- to 60-gram doses of electrolyte can be administered on the trail. It is worth reemphasizing that the horse must have access to drinking water when receiving concentrated electrolyte pastes. These pastes are hypertonic (a greater concentration of electrolytes) compared to blood and will effectively draw fluid out of the horse and into the gut if they are not diluted by water. Administering large doses of electrolytes without adequate water intake will result in serious problems, including colic, dehydration, and possibly death.

Why not try to replace all of the electrolytes lost during the ride? The answer lies in the horse's ability to absorb and retain large quantities of electrolytes in a short period of time. Sodium is actively transported across the intestinal wall by an energy-requiring process. The maximal rate of sodium transport is not known. Practical experience has shown that the levels of supplementation described above can be safely administered. Higher levels may be possible, but the risk of complications related to malabsorption will certainly increase.

Post-ride supplementation
Administering 120-280 grams (4-8 ounces) of electrolyte over the 24-hour post-ride period can eliminate most residual electrolyte deficit. A portion of this can be given as a paste shortly after the conclusion of the ride followed by top-dressing of electrolytes on the next two or three meals.

Conclusion
The health and well-being of the endurance horse can be enhanced by proper electrolyte supplementation during training and competition. The level of supplementation should be adjusted to match sweat losses, which are affected by exercise intensity, terrain, and environmental conditions. A well-formulated electrolyte supplement that replaces the quantities of sodium, chloride, and potassium lost in sweat should be used during training. An electrolyte containing calcium and magnesium is recommended to prevent metabolic disturbances such as thumps from occurring during competition. Electrolytes should only be administered when the horse has access to water because both electrolytes and water are needed to maintain optimal fluid balance.

The formation of ordinary rust is not a chemical enigma and is perhaps the most familiar example of oxidation. A mixture of moisture and oxygen chemically attacks metal and in time corrosion creates a reddish-brown, brittle coating that weakens and ultimately destroys the metal. Just as destructive, though invisible to the eye, is the oxidation that occurs at the cellular level in horses and other mammals. The end result of unchecked oxidation in the bodies of equine athletes may be muscular fatigue severe enough to compromise performance.

Oxidation is a normal metabolic process that allows horses to transform the carbohydrates, fats, and proteins they devour in meals to energy-- energy to grow, perform, and reproduce. One unfortunate, although completely unavoidable, spin-off of oxidation is the creation of free radicals, compounds that have the potential to irreparably damage cells. Free radicals are particularly harmful to cell membranes, structures responsible for keeping destructive entities away from delicate inner organelles.

Under normal circumstances, substances called antioxidants thwart much of the wreckage caused by free radicals. However, oxidation speeds up during athletic effort due to increased oxygen consumption and accelerated aerobic metabolism.

In instances of strenuous exercise, natural stores of antioxidants have difficulty providing sufficient protection against the cascade of free radicals generated from aerobic metabolism. Supplementation of antioxidants is therefore necessary to help ward off the ill effects of mass-produced free radicals associated with intense exercise. Horses with an inadequate reserve of antioxidants may experience muscle soreness or stiffness during an exercise bout and prolonged recovery following hard work.

The All-Star Antioxidants
Vitamin E contributes most generously to the natural antioxidant defenses of the horse. The term vitamin E is actually a collective one that encompasses eight distinctive compounds of plant origin.

These eight are divided into four tocopherols and four tocotrienols. Of these only two--alpha-tocopherol and gamma-tocopherol--have antioxidant properties, and alpha-tocopherol is the most biologically active. On the cellular level, alpha-tocopherol embeds in cell membranes and protects cells from the ravages of free radicals. Alpha-tocopherol has an affinity for fat and is therefore attracted to cell membranes, which are composed of polyunsaturated fatty acids.

Feeds typically fed to horses have variable vitamin E concentrations. Cereal grains such as corn, oats, and barley contain minimal vitamin E, and processing may further decrease vitamin activity. Drying corn artificially, for example, reduces the alpha-tocopherol level by as much as 50%. And while vegetable and soybean oils possess substantially more vitamin E than grains, refining can diminish content. Even if they undergo only minimal refining, these oils have such low inclusion rates in diets that their contribution to total vitamin E intake is miniscule.

Horses may derive sufficient amounts of vitamin E from fresh forage or hay; however, the vitamin content abates as forages mature and are harvested. Up to 90% of vitamin activity may be lost between the pre-bloom or boot stages and complete heading out in grasses. Losses also occur in legumes, although to a lesser extent. Storage negatively impacts vitamin composition as well. In one month, for instance, a 50% loss in vitamin E can occur in stored hay.

Because of the irregularity in vitamin E content of forages and other feedstuffs, the nutrient is often added to fortified feeds. Synthetic forms of vitamin E are absorbed well by horses; however, natural forms are far more digestible, and natural tocopherol is thought to be preferentially used by horses during digestion.

Deficiencies of vitamin E are often thought to precipitate nervous disorders such as equine degenerative myeloencephalopathy, a disease characterized by deterioration of the brain stem and spinal cord. Ataxia is the foremost sign of equine degenerative myeloencephalopathy, usually beginning in the hind limbs and progressing to the forelimbs. Equine motor neuron disease, a debilitating neurological affection that may cause profound paralysis and death, is often partially attributed to vitamin E insufficiency. Treatment for both diseases centers on the provision of megadoses of vitamin E, often 10 to 20 times the normal daily requirement. In some cases of equine degenerative myeloencephalopathy, supplemental vitamin E has completely arrested signs, although few horses return completely to normal.

Vitamin E is often linked with selenium, a micromineral that possesses potent antioxidant properties. Because it is an essential component of glutathione peroxidase, an intercellular enzyme that helps prevent the formation of free radicals, selenium is integral in the diets of performance horses. In addition to inadequate antioxidant defenses, a selenium deficiency may be detrimental to the muscular, reproductive, and immune systems.

Vitamin C, often referred to as ascorbic acid, also plays a pivotal role in neutralizing harmful free radicals. Because of its water-soluble nature, vitamin C can work both inside and outside the cell to combat free radical damage. In the exercising horse, perhaps the foremost contribution of vitamin C is its synergistic relationship with vitamin E. Once a molecule of vitamin E inactivates a free radical, its ability to short-circuit others is forsaken. In the presence of vitamin C, however, vitamin E can be regenerated to continue its raid on free radicals. The rejuvenating properties of vitamin C, therefore, make it an essential ingredient in an effective antioxidant supplement.

Vitamin C is not included in the diets of most horses because the liver synthesizes sufficient quantities under normal circumstances. In periods of stress, such as during sustained exercise, vitamin C levels may drop and reduce the efficiency of antioxidant mechanisms in the body. In one study completed by Virginia Polytechnic Institute and State University, 35 endurance horses competing in 80- and 160-km race incurred vitamin C depletion, suggesting supplementation may be necessary to maximize antioxidant defenses.

An antioxidant cocktail has been advocated by human physicians for several years, and the positive effects of such a concoction have proven effective in nourishing the equine athlete as well. A triad of antioxidants including vitamin E, selenium, and vitamin C ensures a degree of coverage not afforded by vitamin E alone.