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Primary gastric impaction is a usual primary cause of colic in adult horses. There does not appear to be a breed or gender pre disposition, and the disease occurs in mature horses.
The etiology of gastric impaction is unclear in most cases, with poor dentition, rapid food intake, inadequate intake of water, and abnormal gastric motility being mooted as causes of the disease.
Ingestion of thorn apple (Datura stramonium and other species of Datura) cause colic and acute gastric rupture in horses. For cases of undetermined cause, there is usually a history of a diet of mature grass, alfalfa hay, corn, sorghum fodder, or ensilage.
Other causes include: insufficient access to water, poor teeth causing poor digestion, or the atony of old age. Some affected horses have histologic abnormalities of the stomach or intestine, but the clinical importance of these lesions in development of the disease is unclear.
The most common clinical sign is inappetence with or without colic. Heart rate and respiratory rate are usually not markedly elevated and rectal examination does not reveal diagnostic abnormalities. If the stomach has ruptured, there will be signs of septic peritonitis with toxemia and cardio vascular compromise including: sweating, tachycardia, delayed mucous membrane capillary refill time, and discolored mucous membranes. Signs of longterm (chronic) disease include weight loss; intermittent colic; anorexia; dullness; and passage of small amounts of hard, dry feces.
Gastroscopy confirms the diagnosis by visualization of large amounts of ingesta in the stomach or phytobenzoars.
At exploratory laparotomy, the stomach is enlarged with dry, fibrous feed material but is not grossly or acutely distended, and the intestines are relatively empty.
Treatment includes restoration of normal hydration, which can aid in passage of the impaction. Judicious administration of lubricants (mineral oil) or osmotic cathartics (magnesium sulfate and sodium sulfate) or water might aid in softening the impaction.
Analgesia should be provided as needed preferably by use of drugs that do not inhibit gastrointestinal motility.
Rupture of the stomach can occur and is invariably fatal.