Fiber, Protein, Water, and Electrolytes for Heavily Exercised Horses

Fiber (hay/pasture) is an energy source that is often overlooked in horse nutrition. Horses have a highly developed hindgut that houses billions of bacteria capable of fermenting large quantities of plant fiber. Volatile fatty acids (VFAs), the end product of fiber fermentation, are absorbed from the hindgut and transported to the liver. Once in the liver, VFAs can be converted to glucose and be stored as liver glycogen or be converted to fat, and be used to fortify the body’s fat stores. Fiber, therefore, can be used as an energy source for a horse being exercised for several hours since fermentation of fiber and absorption of VFAs continue long after a meal has been eaten.

A performance horse’s intestinal health is critical to success. Normally, the digestive system of the horse is active, moving feed ingredients through the length of the tract. Inactivity of the digestive system, due to dehydration or electrolyte imbalances, can cause severe colic and even death. Research conducted in Germany has underscored the importance of fiber in maintaining gut health for horses that exercise for several hours. Studies there have shown that a diet high in fiber resulted in an increased waterintake. Further, animals supplemented with a simple hay and salt diet had 73% more water in their digestive tracts after exercise and approximately 33% more available electrolytes than animals on a low fiber diet. The additional water and electrolytes in the digestive tract of the high-fiber animals is probably due to the high water-holding capacity of plant fiber. More importantly, the water and electrolyte pool created by a high-fiber diet can be used to combat dehydration and electrolyte imbalances that derail so many endurance horses.

Another important attribute of a digestive system full of fiber is maintenance of blood flow to the digestive system during exercise. The physical presence of fiber in the digestive system will help insure that blood is not totally diverted away from the digestive system with the onset of exercise. In one study, the percentage of cardiac output (blood flow) distributed to the digestive system was higher in fed ponies compared to fasted ponies during exercise. For performance horses, maintenance of blood flow to the digestive system will aid in the ability of gut tissue to remain active and could prevent colic.

In addition to hay and grass as fiber sources, there are so-called “super fibers” that have the same beneficial aspects of forage fibers for maintaining gut health and fluid and electrolyte balance, but contain more energy. The additional energy is the result of both a high fiber content and a low lignin (nondigestible fiber) component. Therefore, these ingredients have more fiber available for microbial digestion. These super fibers (beet pulp, soybean hulls, almond hulls, oat hulls) contain energy equivalent to oats and barley, but they are safer to feed because they do not produce the symptoms of grain overload.

If the protein intake of an exercising horse exceeds its requirement, then the extra protein can be used as a source of energy. The amino acids associated with the extra protein are broken down by the liver, and the nitrogen is excreted as ammonia. The carbon skeletons that are left can be oxidized to produce ATP or used to make glucose or fat. Excessive protein intake should be avoided in heavily exercised horses for a number of reasons. First, water requirements increase with increased protein intake. This can be devastating for horses performing some types of exercise such as endurance racing, where they typically struggle to maintain proper hydration. Second, accumulation of nitrogen end-products (ammonia and urea) in the blood can lead to nerve irritability and disturbances in intestinal function and carbohydrate metabolism. Further, increased ammonia excretion in the urine may lead to respiratory problems associated with ammonia buildup in the stall.

Energy metabolism within the body is not 100% efficient. A certain amount of energy is lost from each chemical reaction in the form of heat. In order for the horse to remain healthy and continue to exercise, excess heat must be dissipated from the body. If the horse is unable to rid itself of this heat, body temperature can rise to the point where it becomes life-threatening. For horses, the main route of heat dissipation is through a form of evaporative cooling known as sweating. In evaporative cooling, the sweat gland takes fluid from the circulatory system and secretes it out to the surface of the skin. Once the hot fluid (sweat) is on the skin, it spreads out and evaporates. This takes heat away from the body. Unfortunately, sweating also takes water and electrolytes away from the body.

As water is lost from the blood, the remaining blood becomes thicker. This increased blood viscosity decreases perfusion potential and negatively influences tissue oxygenation. With intense exercise, water loss can become so extreme that blood volume is decreased and further sweating is not possible. If the horse is not rehydrated, death from heat stroke will occur. Idle horses may drink 10 to 12 gallons of water each day, and for horses performing in hot, humid environments, this requirement may be doubled or tripled.

Electrolytes are substances that dissociate in solution into electrically charged particles called ions. In horses, electrolytes play an important role in maintaining osmotic pressure, fluid balance and nerve and muscle activity. During exercise, sodium, potassium, chloride, calcium, and magnesium are lost in the feces, urine and sweat. Loss of these electrolytes causes fatigue and muscle weakness, and decreases the thirst response to dehydration. Therefore, it is vital to replenish electrolyte losses in performance horses that sweat heavily. Excellent commercial electrolyte supplements are available in both powder and paste forms.

SOURCE: KER

Do Horses Need Magnesium Supplements?

Magnesium has an important role in muscle and nerve function. Horses that are deficient inmagnesium may be unusually spooky and excitable, and they may have muscle tremors or cramping. However, this deficiency is rare because grass and hay normally contain sufficient magnesium to meet the horse’s requirements. Giving a horse too much supplemental magnesium may have no effect at all on nervous behavior or muscle cramping, and may cause serious digestive and metabolic problems.

There are several factors that can decrease the magnesium content of pasture plants. If the soil in a region is deficient in magnesium, growing plants will have a lower content. Lush spring grass has a high moisture content that tends to dilute other nutrients, so each mouthful of this grass will have less magnesium than what would be found in a similar mouthful of summer grass. Diets that are unusually high in potassium can reduce the horse’s ability to absorb magnesium. Finally, intensely exercised horses lose some magnesium in their sweat.

Even if one or more of these conditions exists, horses are not likely to need much, if any, supplementary magnesium. A veterinarian can draw blood for analysis to see if the horse is low in magnesium, and an equine nutritionist can suggest the best way to supplement if this is needed. Because horses are always replenishing magnesium as they graze or eat hay, owners who decide to supplement this nutrient should err on the low rather than the high side to avoid diarrhea and other problems in their horses.

SOURCE: KER

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Vital Signs: Know What’s Normal for Your Horse

When you read a book or magazine article that talks about a horse’s vital signs, the normal rates are almost always given as a range rather than a single number. That’s because an individual equine’s pulse, respiration, temperature, and other signs will be influenced by the horse’s age, stress level, location, health status, fitness, and the time of day, to name a few factors. A young horse taken to its first show or trail ride might have a much faster pulse than an older horse that’s relaxing in its familiar stall at home, and a horse with an infection would probably have a higher temperature and faster breathing rate than one in good health.

When a veterinarian is called to examine your horse for any reason, he will probably check these vital signs and use the results to help determine what may be wrong. You should know the ranges that are normal for your particular horse in order to compare them with whatever the veterinarian has found. To learn about your horse’s vital signs, it will be necessary to take several readings at various times and note any changes you observe.

Checking heart rate is easiest with a stethoscope placed on the girth line just behind the horse’s left elbow. You may have to move the stethoscope around a bit to find the “lub-dub” sound that the heart makes. You can also slide your fingers under the horse’s jaw and feel for the pulse; keep checking by pushing your fingertips outward against the jawbone. The horse’s pulse will rise when you enter the stall, especially if you are carrying tack or are accompanied by a stranger. It will also be higher when the horse is excited or stressed for any reason such as being at an unfamiliar location, in the presence of strange horses, or faced with an unusual stimulus of any kind. The pulse will generally rise with fever, pain, fear, stress, or exertion. It may be lower in horses in top athletic condition and also in horses that are in shock or hypothermia. The normal range is from about 30 to 45 beats per minute for mature horses; foals will have a more rapid pulse.

Counting respiration can be done by watching the ribcage expand and contract, by seeing the horse’s nostrils flare, or by cupping a hand loosely over a nostril and feeling the exhaled breath. The normal range is about 8 to 16 times per minute, generally faster in horses that are nervous or in pain and slower in those in shock, hypothermia, or drug-induced depression. Fit horses also breathe somewhat more slowly; those with colic, discomfort, or heat exhaustion breathe faster, as do horses that have been exercised recently.

Finding the horse’s temperature is probably the simplest chore because a digital thermometer is used for this reading. While someone else is holding the horse, pull the tail out of the way with one hand and slip the lubricated tip of the thermometer about two inches into the horse’s rectum with the other hand. Don’t let go; the thermometer can disappear if the horse tightens its sphincter muscles! When the thermometer beeps or indicates the reading is complete (this make take a minute or two), withdraw the thermometer and check the temperature. The normal range is about 99.5 to 101.5 degrees F, but can be higher in horses with infection, pain, or exposure to strenuous exercise. Horses that have been exposed to high environmental temperatures may also show a rise in body temperature. Lower readings will be seen in horses that are in shock or have hypothermia.

If you have trouble checking your horse’s vital signs, ask your veterinarian to help you learn the proper procedures. You can also find out how to check gum color, dehydration, gut sounds, and the horse’s digital pulse (taken at the fetlock). Knowing the normal readings for your equine will help you and your veterinarian determine what may be wrong with the horse.

Source:KER Newsletter

Swollen or Filled Legs: What’s Wrong With Your Horse?

Horses can rapidly develop swelling or “filling” in one or more legs. Is it serious? What causes it?

A common reason for filling is inactivity in a horse that is accustomed to moving around. An example might be a horse that is usually turned out in the pasture but has been kept in a stall overnight, maybe at a show or in preparation for an early ride the next day. The owner notices that the horse’s rear legs are puffy and swollen as he’s led out of the stall. The legs are not uncommonly warm, and the horse may move somewhat stiffly but is not truly lame. Caused by inactivity and reduced lymph flow, this “stocking up” is usually not serious and will dissipate as the horse is exercised. It’s more common in older horses and can affect all four legs, though stocking up is often seen only in the hind legs.

If your horse has leg swelling accompanied by lameness, warmth in the leg or hoof, or an elevated body temperature, it’s time to call the veterinarian. This is more than simple stocking up.

Swelling in a single leg is likely to signal a serious condition. Horses can “blow up” a leg in response to a scratch, cut, or puncture wound that may be so insignificant that it’s hard to find. The leg may be warm in addition to being swollen. This swelling isn’t likely to go down until the wound is cared for and any infection is treated.

A horse that has significant swelling in all four legs may have some type of systemic illness. This could be a sign of heart trouble, liver or kidney disease, or a bacterial or viral infection. It’s defintely a situation that calls for a veterinary examination. 

Source: KER Newsletter

Importance of Vitamin E for Horses

Vitamin E has numerous functions in the body, many of which are still not completely understood. Vitamin E is essential for the integrity and optimum function of reproductive, muscular, circulatory, nervous, and immune systems.

Its action as a natural antioxidant is seen as the underlying factor of most vitamin E functions. Vitamin E is considered to be the most effective natural lipid-soluble chain-breaking antioxidant. The action of vitamin E is very important in cell membranes, protecting them from peroxidative damage. This is especially important in the mitochondrial membrane, where enzymes involved in respiratory chain energy production are located. Selenium, like vitamin E, also acts to prevent lipid peroxidation, but with differing mechanisms. The two complement each other, one appearing to be able to compensate for the absence of the other to a certain extent. Signs of vitamin E deficiency, such as nutritional muscular dystrophy, are often the same as those seen with selenium deficiency. Other diseases associated with low serum vitamin E include degenerative myelopathy and degenerative myeloencephalopathy.

There are at least eight forms of vitamin E found widely distributed in nature: four tocopherols and four tocotrienols. The majority of vitamin E activity in animal tissues is generally assumed to be alpha-tocopherol and when it is present it is used preferentially. Tocopherols are extremely resistant to heat but readily oxidized. Natural vitamin E is subject to destruction by oxidation, a process that is accelerated by heat, moisture, rancid fat, and certain trace minerals. Horses have the capability to store much less vitamin E than vitamin A. However, stores are thought to be able to compensate for about four months or more of inadequate vitamin E intake.

Vitamin E is abundant in green growing pastures, particularly in alfalfa (lucerne). The content diminishes with maturation, especially after the plants go to seed. Harvesting the forage diminishes the quantity of vitamin E present, and storage of the hay further decreases the amount of vitamin A by as much as 50% in the first month. Vitamin E is abundant in the germ of grains and oils pressed from the germ. Vegetable oils such as corn and soybean oil are relatively high in vitamin E. In practice, the vitamin E content of other feedstuffs is variable and not readily predictable because of handling and storage time. Therefore, it is common practice to supplement animal feeds with vitamin E. Since esterification stabilizes vitamin E, commercial supplements usually contain tocopheryl acetates.

Vitamin E appears to be the most researched vitamin at this time in production animals. Several studies have reported evidence of oxidative stress occurring with exercise in both humans and rodents. Since the main function of vitamin E is to protect the cell against peroxidative damage, lipid peroxidation as a result of exercise may be influenced by the concentration of vitamin E present in the diet. Signs of vitamin E toxicity in the horse have not been produced.

Back Pain in Horses

Wringing the tail, throwing the head, jigging, bolting, not standing still to be tacked up or mounted, refusing to pick up a lead or a gait…these are only a few of the behaviors horses might show when they have back pain. Some of these signs are more subtle than others, and they may come and go over the course of time, making it difficult for owners to pinpoint what is causing them. A veterinarian can often diagnose back pain in a horse, but in some cases, even a professional may have trouble telling just where the horse’s pain is.

Back pain in horses can be caused by a number of factors includingarthritis, malformed vertebrae, injuries, overwork, or a training program that asks for a higher level of performance than the horse has been prepared for. Horses that develop back pain from being ridden may have strained some of the muscles that help to move and stabilize the back. When pain and inflammation restrict the action of these muscles, the job of stabilizing the back falls to other muscle groups that are less able to perform this function.

In horses, the longissimus and iliocostalis muscles lie parallel to the spine for the entire length of the back. These muscles function to flex the horse’s back in both horizontal and vertical planes. The multifidus muscles form a deeper layer and instead of influencing the whole back, each one of these shorter muscles controls only a few vertebrae and the joints between them. When pain occurs, the multifidus muscles fail to stabilize the intervertebral joints as efficiently as they should, and they tend not to recover full function even after the pain has been relieved. Over the course of time, instability increases the horse’s risk for developing arthritis in these joints.

A veterinarian should always perform an examination of a horse that shows signs of back pain. Because back pain can be indicated by a range of behaviors, owners should consider the possibility that back pain might be a cause of resistance, other training problems, or lameness elsewhere, such as the hocks. Ruling out this factor may clarify training decisions such as whether to give the horse a break or try a different approach to teaching a new skill.

Humans recovering from back injury have benefited from physical therapy aimed at reactivating muscles that stabilize the vertebrae. Hilary Clayton, a professor in the equine sports medicine department at Michigan State University, has conducted research that shows the same effect can be achieved in horses. If the examining veterinarian feels that stretching exercises would help a horse build or regain strength and flexibility in its back muscles, the owner can incorporate these exercises into the daily schedule. Commonly known as “carrot stretches,” the activities involve the owner holding a carrot or other enticing treat just out of reach to encourage the horse to stretch its neck and back both lengthwise and laterally. Beginning exercises should ask for just a little bend or stretch to be held for a few seconds before allowing the horse to reach the treat (wear gloves to protect fingers from enthusiastic carrot eaters!). Each session should ask for a small increase of effort.

Food for Thought: Details of the Equine Digestive Tract

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.

Shivers in Horses

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.

Vitamin E and Selenium Status in Horses

Vitamin E and selenium both function as antioxidants in the cell. Selenium is part of the enzyme glutathione peroxidase, which breaks down peroxides. Vitamin E is a fat-soluble vitamin that inserts itself into the cell membrane and neutralizes free radicals. Both selenium and vitamin E can offset a deficiency of the other, as long as both are not deficient.

Selenium deficiency or selenium-responsive conditions have been associated with several problems in horses, including white muscle disease, sporadic tying-up, retained placenta,
reduced fertility, masseter (jaw) muscle myopathy, and heart failure or difficulty swallowing in foals.

The best sample to assess selenium adequacy is whole blood. Because erythrocytes cannot produce more glutathione peroxidase, whole blood selenium concentration reflects long-
term selenium status over the lifespan of the sampled red blood cells (120 to 150 days). It is recommended to use royal blue top (trace mineral) tubes when measuring blood selenium concentration. Horses require 0.1 ppm of selenium per kg of dry matter intake (mg/kg); this equates to approximately 1 mg of selenium per day for a 1,000-lb (454-kg) horse.

Serum is the most commonly used sample for measuring vitamin E. The vitamin E requirement is approximately 1 IU/kg body weight/day, or 500 IU/day for an 1,100-lb (500-kg) horse. The source of vitamin E is very important, especially when treating horses for equine motor neuron disease, equine degenerative myelopathy, or other vitamin E responsive conditions. Natural (d-α-tocopherol), water-soluble sources of vitamin E are better absorbed and preferentially used by the horse. Synthetic vitamin E sources (d,l-α-tocopherol) contain a mixture of eight chemically different sources of vitamin E, only one of which is d-α-tocopherol. Studies have shown that natural vitamin E is more bioavailable than synthetic vitamin E and significantly raises both serum and cerebrospinal fluid concentrations of α-tocopherol compared to synthetic vitamin E.

Vitamin E deficient myopathy is a newly recognized cause of muscle loss and weakness. It is unknown if this is a unique problem or an early, reversible stage of equine motor neuron
disease. Affected horses have low serum (<2 µg/ml) and muscle concentrations of vitamin E. Supplementation with 5,000 IU natural vitamin E/day for six weeks has been shown to restore serum and muscle vitamin E concentrations to normal and most horses make a gradual return to normal exercise.

Providing Dietary Protein to Horses

Owners of dogs and cats know that their pets are carnivores—meat eaters—and commercially available food for these animals contains high protein levels similar to what would be found in the diets of wild felines and canines. Horses, on the other hand, are herbivores—plant eaters—and at first glance, it would not seem that grass, the most natural equine diet, would contain a great deal of protein.

However, grasses and legumes, either fresh or dried, usually do contain enough protein for maintenance of idle or lightly worked horses. Grass has a low to medium level of protein and does not contain a large amount of lysine, an essential amino acid. Alfalfa or lucerne, a legume, is an excellent source of protein, with levels that can approach 18 to 20 percent in the best-quality hay. Since horses need only about 10 or 11 percent crude protein as adults, and about 12 to 14 percent during growth, alfalfa could easily supply most or all protein requirements, though a straight alfalfa diet is not balanced for other nutrients.

In general, a mature horse doing little work needs only enough protein to maintain body tissues. Requirements for protein go up as horses are put into an exercise program, and the need increases with the workload because these active horses must build lean muscle tissue. Breeding stallions and late-pregnant mares need protein levels similar to those of horses in moderate to heavy exercise. Lactating mares have the highest protein requirement, up to twice as much as a mature horse in
moderate exercise. Finally, growing horses need high-quality protein as they increase in size and weight.

The National Research Council’s Nutrient Requirements of Horses contains guidelines for the amount of crude protein needed by horses of every size, age, stage of growth, reproductive status, and exercise level. Horse owners don’t need to pick up a copy of this publication, however, if they purchase horse feed that has been formulated and produced by a reputable manufacturer. Feed bags and labels indicate the type and amount of feed necessary to meet the needs of many classes of horses, from mature/idle to growing, lightly worked, heavily exercised, breeding, or retired equines.

Supplementing a forage-based diet by feeding a concentrate according to the bag’s directions will usually provide sufficient protein. Knowing that their equines need more protein than idle animals, owners of hard-working sport horses or lactating mares may wonder whether they should boost dietary protein levels through the use of special protein or amino acid supplements. Studies in both horses and human athletes have shown that this type of supplementation has little or no positive effect.

However, the intensity of the actual training program in that study is somewhat difficult to interpret. Several research experiments conducted at Kentucky Equine Research (KER) and other locations have examined the effects of dietary protein on metabolic responses to exercise. In two of these studies, lactate accumulation during exercise was lower when horses received a diet containing a high level of protein, but in a third study, lactate accumulation was unaffected by dietary protein level. In the KER study, it was found that muscle glycogen was somewhat lower in horses receiving a high-protein diet, while another study showed no effect of protein level on muscle glycogen concentration. At this point, there are no solid research data to support the theory that protein supplementation may be beneficial to equine athletes. Even in human athletes, benefits have only been sporadically reported. Because the branched-chain amino acids are the primary amino acids catabolized during exercise, researchers have also evaluated supplementation of these amino acids (especially leucine). Horses receiving a branched-chain amino acid supplement had lower lactate levels than unsupplemented horses in one study, but this study involved only mild exercise, so results might not apply to heavily worked horses. Further research in this area may turn up some positive benefits of protein supplementation, but at present, there is no recommendation for this practice.

Effect of Adding Soybean Oil to a Horse’s Ration

When fat is substituted for carbohydrate isocalorically (calorie for calorie) in a horse’s ration, blood glucose and insulin responses to feeding are reduced. It was unclear, however, whether this response was simply due to reduced glucose in the diet or if fat affects glycemic response in some other manner. An experiment carried out at Kentucky Equine Research (KER) was designed to evaluate whether adding fat to a grain meal would affect glucose and insulin response to feeding when the level of grain intake remained the same.

Nine Thoroughbred horses were used in this two-period switchback design experiment. Five of the horses were in training and were physically fit, and four were untrained. During period one, each horse was fed 2.27 kg (5 lb) of a grain mix, which consisted of 72% oats, 20% corn, and 8% molasses at 7:00 a.m. Five of the horses were also fed 200 ml (170 g) of soybean oil mixed into the grain. At 8:00 a.m. each horse was given 2.72 kg (6 lb) of mature bluegrass hay. Blood samples were taken from each horse by jugular catheter before feeding and at 1, 2, 3, 4, 6, 8, 10, and 12 hours post feeding. Water was available to the horses at all times. The same procedure was followed two weeks later with the soybean oil added to the grain of the four horses that served as controls during the first period.

Blood samples were collected and analyzed for lactate, glucose, and insulin at the conclusion of the study. Blood glucose was significantly lower one hour after feeding when soybean oil was added to the diet. Glucose remained lower for 3 hours post feeding. After 6 and 10 hours, blood glucose was higher in the fat-supplemented group. Insulin was lower in the fat-supplemented group 1 hour after feeding. After 8 and 10 hours, insulin was higher in the fat-supplemented group. Plasma L-lactate tended to be higher in the control group 4 hours after feeding and higher in the fat-supplemented group 6 hours after feeding.

These data suggest that the addition of fat (soybean oil) to a grain meal will affect glucose and insulin response to feeding. These effects are independent of the amount of carbohydrate in the diet and may be due to differences in the rate of gastric emptying when fat is included in the diet.

This article was based on information in a paper titled “Responses of Blood Glucose, Lactate and Insulin in Horses Fed Equal Amounts of Grain With or Without Added Soybean Meal” by J. Pagan, T. Rotmensen, and S. Jackson.