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Inappetence in HorsesBy Dr. Bryan Waldridge · March 25, 2011

Determining why a horse has decreased appetite or inappetence can be difficult, especially if it is the only clinical sign the horse is showing. Ponies, donkeys, and Miniature horses can quickly develop hyperlipemia (elevated triglycerides in the blood) when they have decreased appetite, and it can become a life-threatening condition. Your veterinarian is an excellent source of advice because a thorough physical examination, blood work, and other diagnostic tests are often needed when faced with inappetence. This article summarizes some of the common causes of decreased feed intake.

Fever.  A horse has a fever when its rectal temperature is greater than 101.5° F or 38.6° C. Many horses that are febrile will go off their feed and will often begin eating once again when treated with drugs to reduce fever. It is very important to determine the cause of fever.

Dental or oral disease. Dental problems are more common in older horses that may have sharp points that hurt the tongue or cheeks. Young horses can have retained caps (deciduous premolars) or incisor teeth that cause pain. Feeding rough forage or hay that contains thorny weeds can cause oral ulceration. This is a frequent cause of oral ulcers when there has been a recent change in hay source. Foreign bodies embedded in a horse's tongue, such as a piece of wire, can be difficult to diagnose without radiographs.

Gastric ulcers. These are often present and not always the cause of apparent illness.  A recent study revealed that over 58% of horses across various disciplines had gastric ulcers based on gastroscopy. Some horses that are ill for other reasons or stressed will eat better when treated with drugs that reduce stomach acid, even though they do not actually have ulcers.

Metronidazole. This commonly prescribed antibiotic has a bitter taste. Some horses treated with metronidazole, even when it has been flavored, will stop eating. Discontinuing metronidazole administration usually restores the horse's appetite. It is always recommended to flavor any oral antibiotic or other drugs with molasses or gelatin powder to encourage horses to stay on feed.

Hindgut acidosis. Increased feeding of starch can overwhelm the digestive ability of the small intestine. When these sugars reach the large intestine, fermentation occurs and lactic acid is produced. Lactic acid irritates the lining of the large intestine and creates a less favorable environment for the normal microflora that ferment forages. Clinical signs of hindgut acidosis can include inappetence, colic, weight loss, loose manure, irritability, and an increased chance of stable vices (cribbing, wood-chewing, or stall-walking).

Other illness. Some horses are very good at disguising sickness. Respiratory infections, such as pleuropneumonia (fluid in the chest) or viral pneumonia, are the most common cause of fever. Horses with impactions of the large colon may not appear overly colicky and often do not have severe, continuous pain.

Lack of green grass. The best way to entice a horse to eat is to hand-graze on fresh, green grass. Many horses that will not eat anything else will still eat grass.

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