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==Aetiology==
==Aetiology==
The specific cause of the impaction is not always apparent(Sanchez) but the obstruction typically consists of excessive dry, coarse ingesta such as straw bedding or poor quality forage.(Sanchez) It may also be composed of foreign bodies, ingested materials that form a mass (such as persimmon seeds or mesquite beans.1-3 in Bliks) or feeds that tend to swell after ingestion.(151-4 in Sanchez) Gastric impaction may be the result of an gastric atony or defective secretion.(Edwards)
The specific cause of the impaction is not always apparent<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref> but the obstruction typically consists of excessive dry, coarse ingesta such as straw bedding or poor quality forage.<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref> It may also be composed of foreign bodies, ingested materials that form a mass (such as persimmon seeds or mesquite beans.1-3 in Bliks) or feeds that tend to swell after ingestion.(151-4 in Sanchez) Gastric impaction may be the result of an gastric atony or defective secretion.(Edwards)
===Predisposing factors===
===Predisposing factors===
*Dental disorders - roughage may be only partially masticated.<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*Dental disorders - roughage may be only partially masticated.<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*Feeding a horse that has signs of colic - there may be poor gastric emptying associated with generalised decreased gastrointestinal motility
*Feeding a horse that has signs of colic - there may be poor gastric emptying associated with generalised decreased gastrointestinal motility
*Rapid consumption of feedstuffs.(Sanchezz)
*Rapid consumption of feedstuffs.<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref>
*Inadequate water consumption.(Sanchez)
*Inadequate water consumption.<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref>
*Secondary gastric impaction has been related to ragwort poisoning(Milne)
*Secondary gastric impaction has been related to ragwort poisoning(Milne)
*Salivation (Edwards)
*Salivation (Edwards)
*Insidious weight loss (if chronic)(Edwards)
*Insidious weight loss (if chronic)(Edwards)
*Spontaenous reflux with gastric contents visible at the nares (in severe cases)(Sanchez)
*Spontaenous reflux with gastric contents visible at the nares (in severe cases)<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref>
In mild cases where signs resolve spontaneously or with analgesics, owners my continue to feed the horse, which only serves to worsen the impaction.(Mair)
In mild cases where signs resolve spontaneously or with analgesics, owners my continue to feed the horse, which only serves to worsen the impaction.(Mair)
*Gastric impaction is suspected if a [[Colic Diagnosis - Naso-gastric Intubation|'''nasogastric tube''']] cannot be passed or if poorly macerated or digested feed material is recovered from the tube when the horse has been starved for several hours. With gastric distension, the gastoroesophageal junction can become distorted making it difficult to pass the tube.<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*Gastric impaction is suspected if a [[Colic Diagnosis - Naso-gastric Intubation|'''nasogastric tube''']] cannot be passed or if poorly macerated or digested feed material is recovered from the tube when the horse has been starved for several hours. With gastric distension, the gastoroesophageal junction can become distorted making it difficult to pass the tube.<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*On [[Colic Diagnosis - Rectal Examination|'''rectal examination''']], the spleen may be displaced caudally and medially (but this is not specific for gastric impaction).<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*On [[Colic Diagnosis - Rectal Examination|'''rectal examination''']], the spleen may be displaced caudally and medially (but this is not specific for gastric impaction).<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*'''Endoscopy''' would be indicated in a chronic case(Mair, Blisk) and may show a full stomach after a fast of 18-24hrs.(Sanchez) However it is not diagnostic for impaction as it is difficult to assess gastric distension by endoscopy.<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*'''Endoscopy''' would be indicated in a chronic case(Mair, Blisk) and may show a full stomach after a fast of 18-24hrs.<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref> However it is not diagnostic for impaction as it is difficult to assess gastric distension by endoscopy.<ref name="Mair">Mair, T.S, Divers, T.J, Ducharme, N.G (2002) '''Manual of Equine Gastroenterology''', ''WB Saunders''.</ref>
*In a small horse or pony, a lateral '''radiograph''' of the cranial abdomen may show the diaphragm displaced cranially
*In a small horse or pony, a lateral '''radiograph''' of the cranial abdomen may show the diaphragm displaced cranially
*[[Colic Diagnosis - Abdominal Ultrasound|'''Ultrasonography''']] may reveal a markedly enlarged gastric echo extending over six or more intercostal spaces on the left side of the abdomen. A marked increase in the thickness of the wall of the stomach may also be imaged. (Edwards)
*[[Colic Diagnosis - Abdominal Ultrasound|'''Ultrasonography''']] may reveal a markedly enlarged gastric echo extending over six or more intercostal spaces on the left side of the abdomen. A marked increase in the thickness of the wall of the stomach may also be imaged. (Edwards)