BASICS
Anorexia is the loss of appetite or lack of desire for food. Some conditions may not lead to complete loss of appetite, but merely reduced food intake.
Anorexia is commonly a sign of systemic disease, including but not limited to GI disease. Reduced food intake can also be caused by various conditions affecting the lips, mouth, tongue, pharynx, esophagus, or stomach, and may include painful conditions, mechanical obstructions, or nervous or neuromuscular dysfunctions.
Anorexia appears to be the result of a modification of central regulation of feeding behavior in the hypothalamus. Many factors and substances may be involved in regulating feed intake. Anorexia associated with alterations of smell and taste has not been shown in the horse. Decreased food intake has been associated with parasitic infections, but the mechanism is unknown. Pain and depression appear to cause anorexia. Serotonin agonists decrease food intake, apparently via central histaminergic activity. The neurotransmitter neuropeptide Y and various cytokines may cause cancer anorexia–cachexia syndrome. Primary disease conditions, such as infection, inflammation, injury, toxins, immunologic reactions, and necrosis, may cause anorexia via cytokine release. In addition, a proteoglycan has been identified on the cell membranes of animals and has been named satiomem. It reduces food intake and may be a satiety or anorexigenic substance.
Signs include a general lack of interest or a lack of interest in certain types of food only.
- Clinical signs depend on the cause of anorexia. They are highly variable and depend on the underlying disease when due to systemic disease
- Common clinical signs in association with anorexia due to difficulty or inability of prehension, chewing, or swallowing of food include:
- Increased salivation (ptyalism), often due to oral or dental disease or inability to swallow (CN IX, X, and XII), or intoxications
- CN abnormalities—hypoesthesia of the face (CN V), neurogenic atrophy of the masticatory muscles (CN V, motor component), bilateral paralysis of facial muscles (CN VII)
- Expulsion of partially chewed food (“quidding”)
- Nasal discharge containing feed material
- Cough due to foreign material entering trachea; aspiration pneumonia can ensue
- Oral lesions
- Masses on the head in association with the mandibles and sinuses
- If anorexia or decreased food intake occurs for prolonged periods of time weight loss, muscle wasting, and poor hair coat are evident. Edema can occur if hypoproteinemia due to decreased protein intake is severe
- Slight jaundice
Anorexia can be a sign of systemic disease, commonly due to GI or abdominal disorders, including colic.
Anorexia commonly occurs after one of the following primary disease processes in any organ system—inflammation, infection (bacterial, viral, fungal, or parasitic), injury, intoxications, immunologic reactions, neoplasia, necrosis, dehydration, electrolyte imbalances, acid–base disorders, severe respiratory distress, uremia, cardiac disease, metabolic disorders, side effects of medications and pain.
Common specific causes include:
- gastric ulcers and pyloric stenosis
- primary GI colic
- peritonitis, colitis
- liver disease
- renal failure, renal tubular acidosis
- hypertriglyceridemia
- pneumonia and pleuropneumonia
- lymphoma and other malignant tumors
- neurologic disease
- cerebral disease
- laminitis
- endotoxemia, sepsis
- administration of metronidazole or valacyclovir (valaciclovir)
- prematurity and dysmaturity leading to muscle weakness in foals
- hypocalcemia, hypomagnesemia, hyponatremia
- congenital myotonia
Common causes of anorexia associated with inability to access, prehend, and swallow food include—pain (lips, tongue, mouth, teeth, mandibles, maxilla, sinuses, muscles, pharynx, esophagus, or temporomandibular joint), mechanical obstructions, and nervous dysfunction (lips, tongue, pharynx, esophagus).
Common specific causes include:
- Inability to access feed, e.g. neck pain preventing the horse from eating from the ground
- Swelling of the lips, e.g. bee stings or snake bites
- Mucosal lesions due to dental “points,” virus-associated oral lesions (vesicular stomatitis), oral ulcers due to contact dermatitis, mechanical injury or phenylbutazone administration, oral lacerations, oral abscesses
- Tongue lacerations, tongue abscesses
- Neoplasia of the mouth or tongue
- Dental disease
- Postsurgical complication after head and neck surgery
- Guttural pouch disease (empyema, mycosis, neoplasia)
- Strangles
- Sinus disease (sinusitis, cysts, neoplasia)
- Neurologic disease affecting CN function, e.g. equine herpesvirus, equine protozoal myeloencephalitis, yellow star thistle poisoning, rabies, verminous encephalitis
- Tetanus, botulism, tick paralysis
- Temporomandibular joint disease
- Rhabdomyolysis affecting masseter muscles
- Mechanical obstruction in mouth, pharynx, or esophagus, e.g. foreign body, choke
- Pharyngitis
- Hyoid bone injury
- Esophageal disease (stricture, diverticulum, megaesophagus, neoplasia, choke, intramural inclusion cysts)
- Persistent right aortic arch, persistent dorsal displacement, epiglottic entrapment
- Compression of the pharynx (cysts—epiglottic, dorsal pharyngeal, aryepiglottic, soft palate, guttural pouch, or laryngeal neoplasia, strangles)
- Hyperkalemic periodic paralysis
- Muscle weakness (foals)
- Ruptured rectus capitus ventralis muscle
Unwillingness to eat can also be due to social factors such as anxiety owing to management problems (e.g. constant interruption, fear, low rank in herd).
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TREATMENT
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