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Diseases of the Horse - CRF Horse Nutrition Guide

Diseases of the Horse

CRF Horse Nutrition Guide
CRF Equine Research Trials

Your horse’s well-being requires regular care beyond proper nutrition. Pay close attention for any signs of ill health and report these to your equine veterinarian immediately. Symptoms for specific conditions are outlined below, but in general, consult your veterinarian if your horse exhibits any of the following:

  • Abnormal discharges from the eyes, nose or other body opening
  • Foul breath
  • Limping
  • Loss of appetite or condition
  • Violent head shaking or scratching, licking or biting any part of the body
  • Roughened coat or hair loss
  • Lumps or open sores

For further information on metabolic disorders, internal diseases, infectious diseases or parasitic diseases, go to the CRF website, For developing a complete anthelmintic program based on local conditions, you should always see your veterinarian.

CRF recommends visiting the American Association of Equine Veterinarians’ website,, for complete guidelines on caring for horses of all ages and stages. Search for a health topic, ask a question in their “Ask a Vet” section or sign up for their online newsletter. As the world’s largest professional association of equine veterinarians, the AAEP is committed to providing resources for the benefit of the equine industry and the backyard horse owner alike.

Nutritional Guidelines for Specific Conditions

Diseases of the horse.Equine Metabolic Syndrome (EMS) and Equine Cushing’s Disease (ECD)

Feed a low NSC diet (for reduction of hyperglycemia and hyperinsulinemia) for horses with EMS and ECD; feed should include high levels of antioxidants (vitamin E, C and organic selenium) to support immune system function, especially for ECD horses. Consider supplementation with extra magnesium (two grams per 100 pounds of body weight) and chromium (one milligram per 100 pounds of body weight) for horses exhibiting insulin resistance. A total diet with a low level of soluble carbohydrates is recommended, especially for horses where occurrence of laminitis is severe. Overweight horses should be kept off lush pastures, muzzled or managed with limited hay in a dry lot. Routine exercise and turnout are essential recommendations, as they will help to decrease insulin resistance and normalize blood glucose and insulin levels.

Colic and Laminitis (Dietary Related)

Control NSC intake and provide additional calories from fat and digestible fiber sources. Limit pasture consumption during spring and early fall seasons due to high levels of plant sugars (fructans). Avoid small grain hays and pastures (oat, rye, wheat and barley) and fescue due to greater sugar content than other cool-season grasses (timothy, orchard grass, and Bermuda grass) and alfalfa.

Tying Up Diseases

Tying up can occur in any breed of horse, and there are many causes. The most common cause is sporadic tying up, which occurs in horses that are exercised beyond their level of fitness. This is usually seen when horses are not regularly exercised and then are overworked. Other causes of sporadic tying up may occur from electrolyte and hormonal imbalances, overfeeding without regular activity, and vitamin E and selenium deficiencies. Genetic causes of chronic forms of tying up disease include Polysaccharide Storage Myopathy (PSSM), which occurs mainly in draft, Quarter Horse, and warm blood breeds. This type of tying up disease has been recently identified as an inherited autosomal dominant trait and is also known as Equine Polysaccharide Storage Myopathy (EPSM). PSSM causes defective carbohydrate storage and utilization and symptoms include muscle stiffness and cramping when exercised, lack of energy, poor performance, difficulty in backing, hind limb weakness and abnormal gait, and muscle loss, especially in the rear.

Recurrent Exertional Rhabdomyolysis (RER) is a separate autosomal dominant genetic form of tying up disease. RER occurs in Thoroughbreds and produces tying up symptoms due to abnormal muscle contractility that involves a disruption in availability of intracellular calcium. Symptoms include muscle stiffness and cramping when exposed to excitement or exercise.

Tying up diseases.Shivers is a neuromuscular disease that typically occurs in draft horse breeds, but can also present in Warmblood, Quarterhorse and Thoroughbred horse breeds. A high fat, low NSC diet provides better muscle function and produces fewer symptoms for these horses.

With all forms of tying up disease, feeds that are based on digestible fiber and fat with low NSC content are recommended. Alfalfa and alfalfa/grass hays are preferred due to a lower NSC content than most grass hays.

Minimize NSC intake by increasing caloric intake from fat and digestible fiber for horses affected with PSSM. This includes low NSC horse concentrates or feeds high in fat and fiber content, rice bran and vegetable oils. The most effective way to decrease dietary NSC content is to add vegetable oil. Keep increasing the fat content until the horse is free of symptoms for PSSM or shivers. A supplement or balancer pellet may be required to meet the vitamin and mineral requirements due to the low rate of concentrate provided due to the large amounts of oil fed.

Provide a diet low in NSC for horses with RER to reduce excitable behavior and incidence of symptoms. Feeding additional calming agents above required levels (magnesium and vitamin B1) might also reduce excitable behavior and symptoms in horses with RER.

Chronic Obstructive Pulmonary Disease (COPD) or Heaves

Minimize or eliminate dust and mold from the diet by utilizing feeds that reduce the amount of hay fed. Complete feeds with a high fiber content based on beet pulp or soy hulls, with a crude fiber guarantee of at least 15 percent can be fed safely with a minimum of hay (0.5% of body weight daily). Feed high quality hay soaked in water, chopped hay or hay cubes. Reduce environmental dust and mold by replacing straw bedding with wood shavings or provide pelleted wood bedding or processed paper-based bedding material. Increase ventilation in the stall and provide for as much turnout as possible. Complete feeds or supplements containing higher levels of omega-3 fatty acids (found in rice bran, soy oil, flax seed and fish oil) competitively inhibit activity of the cyclooxygenase enzyme, which is necessary for eicosanoid or prostaglandin production, and can be helpful in decreasing inflammation of the respiratory system.

Hyperkalemic Periodic Paralysis (HYPP)

A horse suspected of being N/H or H/H forms of HYPP should be on a low potassium diet. Select feed and hay with low potassium content (1.2% or less for total diet). Oats may be fed with a supplement pellet or a high fiber complete feed can be fed along with a limited amount of hay. Avoid potassium-containing electrolytes and mineral supplements, as well as molasses, orchard grass hay, alfalfa hay (baled, cubed or pelleted) or wheat bran, as they contain high levels of potassium.

Excitable Behavior

The exact mechanism or cause for excitable behavior in the horse is not known. Horses that are overfed and underworked can exhibit excitable behavior, as well as those that are stabled for long periods of time (as compared to horses allowed to graze for 16 to 18 hours daily). Horses may also exhibit stereotypic behaviors such as cribbing, wood chewing and stall weaving as a means to relieve stress. Feeding large amounts of grain is associated with increased gut acidity. High grain diets may cause pain due to increased gut acidity and ulcer formation, which can serve as a stimulus for stereotypic behavior. Excess grain can also lead to starch overload in the hindgut and can result in serious metabolic disorders such as colic, laminitis and insulin resistance. Reducing NSC and adding fat to the diet has resulted in lowered blood glucose and insulin levels and often effects calmer behavior in the horse. Feeds high in fat and digestible fiber are recommended, as fat and fiber do not increase blood glucose or insulin levels; neither do they contribute to increased lactic acid from fermentation in the hindgut. Select a horse feed with a low level of NSC and based on digestible fiber sources such as beet pulp, soy hulls, rice bran and alfalfa meal.

Equine Protozoal Myelitis (EPM)

EPM is a neurological disease. Diagnosis of EPM is based upon finding antibodies, or more recently, a DNA detection test from blood or cerebrospinal fluid. A feed low in NSC with a high content of digestible fiber and fat is recommended since there is an increased incidence of diarrhea as a side effect of treatment. High-quality forage is indicated also as weight loss is a common symptom of horses afflicted with EPM. High levels of folic acid and vitamin E should be present in the feed, or added as a supplement to help rebuild damaged nerve and muscle tissue. A horse feed with quality protein (soybean meal as protein source) and high levels of limiting amino acids (lysine, threonine and methionine) is also recommended to rebuild damaged muscle tissue.

Gastric Ulcers

Higher intensity levels of training and competition are correlated with an increase in the incidence of ulcers. Horses suffering from ulcers should be treated immediately. Allowing the horse to be turned out and graze 24 hours daily will help to alleviate ulcers as the stress level will be reduced and increased saliva production will help reduce stomach acidity and prevent further damage. Fermentation of fat and fiber will not produce lactic acid, selection of a horse feed with high levels of fat and digestible fiber and low levels of NSC will reduce fermentation and acid production in the stomach and small intestine where ulcers form. Providing enough hay in the diet is important to insure adequate salivary bicarbonate to buffer stomach acidity. Feeding a daily buffer or antacid product may be required to maintain an ulcer-free condition. Alfalfa or a legume\grass mixed hay may be preferred due to the higher calcium content and potential stomach buffering capacity. Increasing the frequency of feeding can be helpful in keeping stomach pH less acidic with more constant saliva production and the dilution effect of a more consistently full stomach.

Colonic Ulcers or Right Dorsal Colitis

Like gastric ulcers, colonic ulcers are found more often in performance horses than in horses not in performance activities. There is also a strong association with the use of non-steroidal antiinflammatory drugs (NSAIDs) and colonic ulcers. Colonic ulcers with symptoms including mild colic symptoms, lethargy and partial anorexia can progress to Right Dorsal Colitis (RDC) with anorexia, fever and diarrhea causing dehydration and weight loss.

Treatment of RDC includes discontinuing use of NSAIDs, decreasing gut fill to allow the colon to rest, reducing inflammation and restoring normal colon absorptive function. Reduce gut fill by decreasing the amount of long-stemmed hay in the diet. Replace most of long-stemmed hay with a high-fiber (15 percent crude fiber or greater) complete feed. Feeding a complete feed at one percent of body weight daily and chopped, cubed or baled hay at 0.5 percent of body weight daily will meet or exceed the maintenance requirements of most horses. This feeding program reduces gut fill and decreases the mechanical load on the colon. The horse can also be allowed to graze small amounts of fresh grass for short periods (10 to 15 minute intervals up to six times daily) to assist in weight gain. The dietary changes should be made over a week’s time to allow the gastrointestinal tract time to acclimate. The complete feed diet should be continued for three to four months or until hypoproteinemia and hypoalbuminemia has been resolved.

Psyllium husk can also be added to the diet to shorten transit time of ingesta and increase water content of the GI tract. Complete feeds or supplements containing higher levels of omega-3 fatty acids (found in rice bran, soy oil, flax seed and fish oil) competitively inhibit activity of the cyclooxygenase enzyme, which is necessary for eicosanoid or prostaglandin production, and can be helpful in decreasing inflammation of the colon.

Minimizing stress will also be helpful in controlling RDC. Stall rest, reduction in strenuous exercise or training and reduction in transport activities are ways to reduce stress. Horses should also have adequate amounts of clean fresh water and provided a complete mineral with salt to ensure adequate water intake.


Reducing caloric intake and increasing caloric expenditure through exercise are the two methods that must be used to reduce excess body weight. The most effective method to keep horses from becoming overweight is to control intake of feed, hay and pasture. Horses on lush pasture may be fitted with grazing muzzles or placed in a dry lot and fed moderate quality grass hay. Weigh the feed and hay to determine the amount fed and adjust the feeding rate to maintain an appropriate body condition score. Weight gains and losses can also be monitored with a weight scale or weight tape. The use of a concentrated feed or balancer pellet allows sufficient intake of minerals and vitamins while reducing calories associated with reducing conventional horse feeds to less than 0.5 percent of body weight (i.e. less than five pounds daily for a 1,000-pound horse). Another way to ensure adequate mineral and vitamin intake when feeding a reduced amount of a conventional horse feed is to provide a mineral/vitamin supplement. Horses in training should be fed a lower-calorie feed but in sufficient amounts to meet dry matter and other nutrient requirements (minimum of 1.5 percent of body weight daily for total diet).

Weight Loss

Feed horses needing to gain weight a diet high in fat and digestible fiber to increase caloric intake safely without a risk of colic and laminitis from a diet high in soluble carbohydrates. Fat contains 2.25 times more calories than any other nutrient, so high-fat feeds and supplements will provide the most calories for weight gain. Digestible fiber sources (beet pulp, soy hulls and alfalfa meal) used in many horse feeds are relatively high in calories and low in starch, and provide a safety margin when fed at high rates to increase weight gain. High-quality forage should be selected, as it is more palatable, allowing greater intake, and has a higher caloric density, providing more calories per pound. Feeds containing yeast culture, probiotic bacteria, digestive enzymes and other feed additives that enhance digestion are useful in adding weight to thin horses.

Kidney Disease

Horses with kidney or renal disease should be maintained on a strict diet to limit protein, phosphorus and especially calcium, as reduced kidney function enables the formation of calcium oxalate stones in the urinary tract. Avoiding feeds or supplements high in protein, calcium or phosphorus for horses with renal disease, means avoiding all commercial feeds. The only grain recommended is a limited amount of whole or crimped oats. Feeding legume hay such as alfalfa or providing a diet with excess protein does not cause kidney disease in healthy horses, but is not recommended for horses with renal disease. Avoid feeding beet pulp and wheat bran due to high levels of calcium or phosphorus. Use caution with salt supplementation as some horses may overeat salt. Instead of allowing free-choice consumption of salt, add one to two ounces of plain salt to the feed daily.

Liver Disease

Horses with liver or hepatic disease should be fed easily digested NSC sources in order to maintain blood glucose levels, and diets high in fat or protein are not recommended. Horses with hepatic failure should be supplemented with B-complex vitamins and ascorbic acid (vitamin C) as the liver is the site of all vitamin syntheses.

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