Nutrition is an important part of the management and treatment of sick horses. Stresses (eg, surgery, severe orthopedic problems, and infection) can substantially increase caloric needs because of an increase in catabolism. In addition, anorexia or dysphagia can lead to inadequate intake. The consequences of not providing proper nutrition include impairment of the immune system, delayed wound and fracture healing, hypoproteinemia, muscle wasting, and weakness. Generally, supportive nutritional therapy should be considered if an adult horse has been hypophagic for ≥ 3 days. Neonatal foals require energy and protein supplemental intake within 24 hours of deprivation.
Pearls & Pitfalls
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The exact energy and protein requirements of sick horses are not known and will likely vary depending on the age, level of fitness, disease state, and environment of the individual animal. The increased metabolic demands of recovery from surgery or illness may be balanced by a decrease in overall activity during hospitalization; metabolic energy needs for maintenance of normal, healthy individuals may be appropriate. However, patients that have experienced severe trauma, sepsis, intestinal resection, or substantial devitalized tissue may require additional nutritional support. In general, the old adage "if the gut works, use it" rings true if trying to decide between enteral and parenteral nutrition. Enteral nutrition, even in small amounts, is important to help maintain overall gut health and function (1).
The order of nutrient priorities for most clinically ill equids is water, energy, electrolytes, and protein. Water-soluble vitamins (all B vitamins; vitamin C) are poorly stored in the body and should be supplemented during periods of prolonged (more than a day or two) stress.
There are several methods of providing nutritional support to a sick horse. The simplest is to encourage the horse to eat on its own, if possible. Unusual feed preferences might be noted. If the horse won't eat its usual diet, offering small amounts of novel, appropriate feeds and letting the horse choose can determine what is most palatable to the animal. Many horses will eat fresh green grass even if they refuse other feeds. Alfalfa hay is more palatable than grass hays but can be contraindicated in some cases. Sweet-feed mixtures of grains and molasses usually are the most appetizing of concentrates but should be used sparingly in most cases. Bran mashes are usually palatable, but the calcium and phosphorus intake should be balanced. The addition of molasses, applesauce, carrots, and flavors such as peppermint might increase acceptance of feed in anorectic horses.
If pain or fever is causing inappetence, analgesics can improve food intake. Anti-inflammatories such as dipyrone, flunixin meglumine, meclofenamic acid, and phenylbutazone can be used with caution, depending on the disease process. Whether or not prolonged use of phenylbutazone causes equine gastric ulcer syndrome is controversial. Studies of horses receiving the drug at recommended doses clinically for 15 days did not have an increased risk; however, horses receiving supraphysiological doses did (2).
Nasogastric tube feeding is another way to provide nutrition to horses that will not (or cannot) eat voluntarily. A nasogastric stomach tube can be passed several times a day or left in place, secured with tape or sutures as an indwelling feeding tube. This is an especially effective method to provide nutrients to sick neonates. It is also an inexpensive method to replace fluid and electrolyte losses. Soaking a complete pelleted feed in water also can make a slurry for tube feeding; however, the mixture needs to be sufficiently dilute to prevent clogging the tube.
The third method to provide energy nutrition to sick horses is total or partial parenteral nutrition (TPN or PPN). IV fluid administration can maintain hydration in horses unable to maintain hydration, for whatever reason, voluntarily. The most common clinical fluid replacement solutions are saline solution (0.9% NaCl), lactated Ringers, and 5% dextrose. The nutritional value of these fluids is minimal. Fat and amino acid solutions are available but are expensive and require dedicated IV administration lines. TPN is costly and requires intensive care and monitoring, which limits its usefulness in adult horses.
After nonabdominal or simple intestinal surgery, most horses resume enteral (or partial enteral) feeding within 6–12 hours. Horses that have had small intestinal resection and anastomosis can require more time, but recommendations vary. Reports range from 2 to 10 days (3). The rationale for withholding enteral nutrition is to allow the anastomosis to heal and decrease risk of impaction and ileus. However, enteral feeding is critical to maintain the GI mucosa and regain overall GI function (nutrient absorption and motility). Exact nutritional requirements for horses post–colic surgery are unknown (3).
Nutrition for Specific Diseases/Problems in Horses and Other Equids
Equine Asthma
Equine asthma may be caused by sensitivity to dust and molds found in hay. Affected horses may improve when hay is soaked in water or steamed before feeding or, less desirably, removed from their ration (in which case the horse is placed on a complete ration that is pelleted and/or contains an alternate roughage source such as beet pulp or chopped forage). However, some horses with asthma are allergic to pollens and weeds, so a thorough clinical workup as to cause should be performed before drastically altering the ration/management. Note that, for allergy testing, either an elimination diet or the intradermal test is recommended because serum testing for allergies is not considered reliable in horses (4, 5).
Diarrhea in Horses and Other Equids
Diarrhea in horses is primarily a colonic disease. Traditionally, affected horses are managed by feeding less grain or concentrate and more hay or other forage. This increase in dietary fiber can bind water and result in better-formed feces. If weight loss is a concurrent problem, maintaining concentrate intake could be better; however, products with lower (ie, ≤ 20%) nonstructural carbohydrates (NSCs) may be recommended.
Grain is digested mainly in the small intestine, and hay in the large intestine. Unless the small intestine is also affected, feeding grain or grain-based concentrates can help maintain body mass. When introduced slowly, prebiotic, digestible fibers such as beet pulp can support a healthy microbiome and potentially help horses affected with diarrhea. Providing electrolytes can also help prevent dehydration as a result of chronic and/or excessive diarrhea. Ideal probiotic supplementation for horses remains to be determined. (Also see Overview of Colic in Horses and Infectious Diarrheal Diseases in Horses.)
Free Fecal Water Syndrome in Horses and Other Equids
Free fecal water (FFW) syndrome in horses is of unknown cause, and ideal feeding and management practices have yet to be defined. However, a study of European horses reported that horses with FFW were fed higher amounts of concentrate feeds and total water-soluble carbohydrates, along with lower amounts of crude protein and fiber, than non-FFW horses (6). Other work has noted that social stress (ie, being lower in herd hierarchy) might be a risk factor for horses with FFW (7).
A thorough health checkup is recommended, followed by an evaluation of overall diet to ensure balance and proper nutrient intake and to assess fiber and forage quality. Special attention should be paid to any supplements and ingredients being fed, because oversupplementation or unregulated supplements with poor ingredients can potentially disrupt the diet. Forage type and/or source might need to be carefully altered, depending on the individual's needs.
Hepatic Disease in Horses and Other Equids
In horses with hepatic disease, the major concerns are providing adequate protein and energy, thus easing the liver’s role in energy production and decreasing the amount of metabolic waste to which the liver is exposed. Parenteral or enteral glucose administration can be important as an energy source in anorectic horses.
Grazing can be encouraged, although it should be monitored, according to the horse's individual needs. Grass hay is a preferred forage choice, and legumes such as alfalfa should be avoided. Concentrate feeds might be necessary to provide a glucose source and decrease the demand for hepatic gluconeogenesis. In horses that are concurrently insulin resistant, the bolus of glucose per meal should be limited. Meals should be divided into multiple small offerings (ie, 4–6 small meals) and mixed with forage throughout the day.
Adding oil or fat to the diet provides energy and essential fatty acids and can start around 0.1 mL/kg BW vegetable oil, as long as fat malabsorption is not occurring. Horses with hepatic disease may need supplemental protein; however, large amounts per meal should be avoided. Careful inclusion of high-quality protein is recommended, especially if forage quality is poor (8).
Chronic Kidney Disease in Horses and Other Equids
Chronic kidney disease (CKD) is uncommon in horses; however, nutritional management is critical when it is diagnosed. A key challenge is to maintain body condition. Appetite can vary from day to day, but horses with CKD often prefer pasture grass. If pasture grass is unavailable or requires supplementation, grass hay is recommended over legume (alfalfa), because the latter tends to be higher in protein and calcium, which could tax the kidneys unnecessarily if provided in excess. Mixing in a small amount of legume hay to encourage eating might be necessary in some cases.
Concentrate feeds with lower crude protein (ie, 10%) may be necessary to support condition. Grains, such as oats, are palatable but must be balanced, because grains do not contain sufficient vitamins or minerals. A low-protein (12–18%) ration balancer may be used for a horse that does not require concentrate feeds but does need vitamin and mineral supplementation; however, the daily amount fed should be divided into two or more feedings.
Providing adequate-quality protein is recommended to meet minimum needs without excess in order to decrease renal stress. A reasonable target protein intake for CKD horses has been reported to be 1–1.5 g/kg BW/day and should include essential amino acids such as lysine, methionine and threonine. Horses excrete substantial amounts of calcium in their urine. In cases of renal disease, controlled (but not insufficient) dietary calcium should be fed, and legume forage and/or beet pulp should be minimized or avoided if possible (9).
Equine Gastric Ulcer Syndrome
Equine gastric ulcer syndrome (EGUS) encompasses both equine squamous gastric disease (ESGD) and equine glandular gastric disease (EGGD). Diets that exceed approximately 23% nonstructural carbohydrates are a known risk factor for exacerbating EGUS (10). Little scientific evidence exists to describe specific dietary recommendations for EGGD (11), and many nutritionists recommend diets similar to what is recommended for managing ESGD. Providing ad lib access to forage, or at the very least not exceeding 4 hours without access to forage, is recommended. Overweight equids, or equids on a weight-management diet, might require the use of slow feeders and/or grazing muzzles to extend consumption time.
Legume forage, such as alfalfa, acts as a natural acid buffer because of typically higher calcium and protein content. For horses with EGUS, concentrate feeds should be used sparingly but may be necessary for maintaining condition. Concentrates with low-moderate NSC content can be fed in multiple small meals per individual needs. Vegetable oils can be used to increase dietary energy content. A study showed that horses receiving a reduced-NSC diet (≤ 23% NSC) maintained lower EGUS scores after cessation of omeprazole treatment than horses that remained on higher-NSC diets, suggesting that dietary modification can play a role in EGUS management (10).
All horses should have access to at least some (0.5 kg [1 pound] for a 500-kg horse) forage just prior to exercise to minimize the risk of acid damaging the mucosal lining of the stomach. Fresh water should always be available. Electrolytes, if given, should be provided with food or diluted in water, because hypertonic solutions or pastes can irritate or exacerbate the effects of ulcers (2).
Myopathies in Horses and Other Equids
Diet plays a critical role in the management of horses with myopathies; however, dietary recommendations for each myopathy are different. Very briefly, horses diagnosed with polysaccharide storage myopathy (PSSM) type 1 have a genetic mutation that increases activity of glycogen synthase at rest and when activated by glucose-6-phosphate, resulting in skeletal muscle concentrations of glycogen 1.5–4 times higher in PSSM type 1 horses than in normal horses. Persistent glycogen synthase activity appears to disrupt normal muscle energy metabolism during exercise. PSSM type 2 is of unknown cause, but affected animals can develop clinical signs similar to those of PSSM type 1 (ie, muscle soreness, reluctance to move).
Dietary management of PSSM type 1 requires a strict limitation of NSCs, with added dietary fat for energy and buildup of oxidative capacity through training. If a horse is overweight, dietary fat might be contraindicated, and a short period of fasting can help to elevate plasma free fatty acid concentration prior to exercise. For PSSM type 1 horses, NSC should comprise no more than 10–15% of daily energy requirements, and fat may comprise 12–15% of daily energy requirements. For PSSM type 2, NSC restriction may not need to be as strict.
Myofibrillar myopathy (MFM) horses develop exercise intolerance and/or intermittent exertional rhabdomyolysis. The disease has been characterized by cytoplasmic aggregates of the cytoskeletal protein desmin in scattered muscle fibers. Currently, there is no recommendation to restrict NSCs for MFM horses, nor is there a need for high-fat diets, as are necessary for PSSM horses (12).A balanced diet for the MFM horse should typically consist of good-quality forage (10–12% crude protein and 10–17% NSC); a concentrate, if necessary (containing 20–30% NSCs, 4–8% fat, and 12–14% crude protein); and a supplement containing N-acetylcysteine and CoQ10 (13).
Neurological Disorders in Horses and Other Equids
Equine motor neuron disease (EMND) is characterized by oxidative damage to somatic lower motor neurons, particularly those associated with oxidative type I muscle fibers. EMND is invariably associated with vitamin E deficiency. From a nutritional perspective, horses diagnosed with EMND should receive a highly bioavailable form of natural vitamin E (d-alpha-tocopherol); the dose depends on the size of the equid and severity of disease but can typically range from 5,000 to 10,000 IU/day. Note that individual needs will vary (14).
Equine degenerative myeloencephalopathy (EDM) most commonly affects horses ≤ 2 years old and is often associated with a deficiency of vitamin E. Vitamin E supplementation is not curative but could be supportive, along with fresh pasture forage (14).
Equine Metabolic Syndrome
Equine metabolic syndrome (EMS) is a collection of risk factors associated with laminitis, with one of the hallmarks beinginsulin dysregulation (ID) (15). From a nutritional perspective, limiting NSCs in the diet is imperative. Nutritional considerations for the metabolic horse will be discussed broadly here; however, specific needs of the individual equid need to be at the forefront of dietary management.
In managing EMS, forage still needs to be the basis of the diet. A forage analysis is the only way to measure NSC content; however, it is not always practical to complete. In such cases, soaking hay helps to decrease NSC content; however, the degree of decrease can vary by variety, water temperature, and soaking time. Generally, soaking hay in warm (room-temperature) water for approximately 30 minutes (up to 3 hours) is recommended, and soaking time increases to approximately 6–12 hours if cold water (8°C [46°F]) is used (16, 17). Hay should be completely submerged in water for soaking, then drained for 20–30 minutes prior to feeding. The amount of NSC removed from soaking varies widely and depends on forage variety and temperature of soaking water. A loss of approximately 10% of forage due to soaking needs to be accounted for when weighing the forage to be soaked (in other words, soak an extra 10% of the ration to help prevent underfeeding). Note that hay steamers will not remove NSCs from forage (18).
A ration balancer should be given to horses on forage-only and/or weight loss diets to ensure proper nutrient intake. Underweight horses may require low NSC (≤ 12% starch plus sugar) concentrates and/or oil supplementation for added calories. A horse with severe ID should be limited to 0.1 g NSC/kg BW/meal, whereas a non-ID horse with an exaggerated insulin response to a meal may be slightly less restricted, up to 0.5 g NSC/kg BW/meal. Practically speaking, a concentrate that contains 12% NSC (starch plus sugar) equates to a maximum of 0.45–2 kg (1–4.5 pounds) per meal (19). Feeding multiple small meals might be required to achieve sufficient calories for underweight or hard-keeping metabolic horses. Although obesity is a major risk factor for ID, horses of normal weight and condition can also suffer from ID and can be of any age or breed.
References
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