Nutrition is an important part of the management and treatment of sick horses. Stresses (eg, surgery, severe orthopedic problems, or infection) can significantly increase caloric needs due to an increase in catabolism. In addition, anorexia or dysphagia can lead to inadequate intake of the proper nutrients. 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 some energy source within 24 hr of decreased intake.
The order of nutrient priorities is water, energy, electrolytes, and protein. Some water-soluble vitamins are poorly stored in the body and should be supplemented. The basal energy requirement (BER) in kcal/day can be calculated by the following formula: BER = 70 (body wt in kg)0.75. For example, BER is ~6,800 kcal/day for a 450-kg horse and 1,300 kcal/day for a 50-kg foal. Severe illness or trauma (eg, barn fire burns) significantly increase these needs.
There are several methods to provide nutritional support to a sick horse. The simplest method is to encourage the horse to eat on its own. Unusual feed preferences may be seen. Offering a variety of feeds and letting the horse choose can best determine what is most palatable to the animal. Many horses will eat fresh, green grass even though they refuse other feeds. Alfalfa hay is more palatable than grass hays. Whole oats and sweet-feed mixtures of rolled grains and molasses are the most appetizing of grains. Bran mashes are usually palatable, but the addition of molasses, applesauce, and salt may increase their acceptance in anorectic horses.
When horses experience pain or fever, analgesics can improve food intake; NSAIDs, such as dipyrone, flunixin meglumine, meclofenamic acid, and phenylbutazone, can be used. Prolonged use of phenylbutazone should be avoided because of the adverse effects of gastric and small-intestinal ulceration and renal papillary necrosis.
Tube feeding is a second way to provide nutrition to horses that will not (or cannot) eat voluntarily. A normal stomach tube may be passed several times a day or may be sutured to the nostril and left as an indwelling feeding tube. This is an effective method to provide nutrients to sick neonates. It is also an inexpensive method to replace fluid and electrolyte losses. Enteral nutritional supplements used in human medicine are particularly useful to provide sufficient caloric intake to adult horses. These products have a known caloric content, which facilitates calculation of the animal’s needs. Soaking a complete pelleted feed in water can make a slurry for tube feeding; however, when feeding a slurry in this manner, the stomach tube may clog with feedstuff.
The third method to provide energy and protein to sick horses is through use of total or partial parenteral nutrition (TPN or PPN). Fluid administration (IV) can maintain hydration in horses unable either to drink or absorb fluids. Common replacement solutions include sodium chloride, lactated Ringer’s, and 5% dextrose. The nutritional value of these fluids is insignificant. Fat and amino acid solutions are also available. The components of parenteral nutrition are glucose, amino acids, lipid, trace minerals, and multivitamins. The resultant solution is hypertonic and is delivered by constant infusion through a jugular catheter. Delivery is optimized through use of a fluid pump. Blood and urine glucose should be monitored twice daily to regulate the rate of infusion. TPN is costly and requires intensive care and monitoring, which limits its usefulness in adult horses.
Horses with recurrent airway obstruction (see Recurrent Airway Obstruction in Horses) are frequently sensitive to the dust and molds found in normal hay. They often improve when hay is removed from their diet and they are placed on a complete ration that is pelleted or contains a roughage source such as beet pulp. They do best on pasture. Another source of dust-free roughage is haylage.
Diarrhea in horses is primarily a colonic disease. Traditionally, affected horses are fed less grain and more hay. This increase in dietary fiber can bind water and may result in better formed feces. If weight loss is a concurrent problem, it may be better to maintain grain intake. Grain is digested mainly in the small intestine, and hay in the large intestine. Unless the small intestine is also affected, feeding grain helps maintain body mass. (Also see Colic in Horses and see Intestinal Diseases in Horses and Foals.)
The role of nutrition in horses with hepatic disease (see Hepatic Disease in Large Animals) is to provide adequate 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 may be important as an energy source in anorectic horses. In horses that are eating, cereal grains should provide adequate carbohydrates. Corn is the grain of choice because of its low-protein, high-carbohydrate content. High-protein feeds, such as alfalfa hay, should be avoided.
Horses excrete significant amounts of calcium in their urine. In cases of renal disease, low-protein, low-calcium diets should be fed. Corn and grass hay are the feeds of choice.