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==Introduction==

==Introduction==

The horse is a monagastric hindgut fermenter. The horse evolved for grazing and it does so for up to 17 hours a day. A high proportion of the horse's dietary carbohydrate is in the form of '''starch'''. A mature horse eats 2-2.5% of it's body weight in dry matter every day, 1.5-1.75% of this should be fibre (hay/haylage). This is to prevent a rapid drop in pH in the large intestine and also to stimulate peristalsis in the gut and prevent build up of gas.

The horse is a monogastric hindgut fermenter. The horse evolved for grazing and it does so for up to 17 hours a day. A high proportion of the horse's dietary carbohydrate is in the form of '''starch'''. A mature horse eats 2-2.5% of it's body weight in dry matter every day, 1.5-1.75% of this should be fibre (hay/haylage). This is to prevent a rapid drop in pH in the large intestine and also to stimulate peristalsis in the gut and prevent build up of gas.

==Oral Cavity==

==Oral Cavity==

'''Premolars'''

'''Premolars'''

:A horse's '''Wolf tooth''' (PM1) is often lacking. Molars and Premolars form a continuous surface. Premolars have a high rate of wear and continually erupt. The upper teeth are wider than the lower. There is no infundibulum in the lower teeth.

:A horse's '''Wolf tooth''' (PM1) is often lacking. Molars and Premolars form a continuous surface. The cheek teeth have a high rate of wear and continually erupt. The upper teeth are wider than the lower. There is no infundibulum in the lower teeth.

====Ageing====

====Ageing====

Horses can be aged by their teeth. At two and a half years of age the first permanent incisor will erupt; at three and a half the second permanent incisor will erupt and at four and a half the third permanent incisor will erupt. Over five years of age the folding of the enamel ring ('''infundibulum''') can indicate age. There is a seven year hook and over 13 years of age a '''dental star''' will be present.

Horses can be aged by their teeth. At two and a half years of age the first permanent incisor will erupt; at three and a half the second permanent incisor will erupt and at four and a half the third permanent incisor will erupt. Over five years of age the folding of the enamel ring ('''infundibulum''') can indicate age. There is a seven year hook and over 13 years of age a '''dental star''' will be present.

The '''Galvayne's Groove''' is a brown groove on the upper corner incisor teeth and indicates that the horse is over 10 years old. At 15 the groove will be approximately half way down the tooth; At 20 the groove will run down the whole tooth; Over 20 the grove begins to disappear; At 25 the groove will only be visible on the bottom half of the tooth. At 30 the groove will usually be gone.

The '''Galvayne's Groove''' is a brown groove on the upper corner incisor teeth and indicates that the horse is over 10 years old. At 15 the groove will be approximately half way down the tooth; At 20 the groove will run down the whole tooth; Over 20 the groove begins to disappear; At 25 the groove will only be visible on the bottom half of the tooth. At 30 the groove will usually be gone.

===Palate===

===Palate===

The jejunum is confined to the left dorsal part of the abdomen associated with a long mesentery. It is restricted to this position by the large [[Caecum - Anatomy & Physiology|caecum]] on the right, and ascending [[Colon - Anatomy & Physiology|colon]] ventrally on both sides.

The jejunum is confined to the left dorsal part of the abdomen associated with a long mesentery. It is restricted to this position by the large [[Caecum - Anatomy & Physiology|caecum]] on the right, and ascending [[Colon - Anatomy & Physiology|colon]] ventrally on both sides.

===Ilium===

===Ileum===

The terminal portion of the small intestine is the ileum, which joins the cecum at its dorsal

The terminal portion of the small intestine is the ileum, which joins the caecum at its dorso-medial aspect. The ileal mesentery attaches to the [[Caecum - Anatomy & Physiology|caecum]] at the dorsal caecal band.

medial aspect. The ileal mesentery attaches to the [[Caecum - Anatomy & Physiology|caecum]] at the dorsal caecal band.

==[[Large Intestine Overview - Anatomy & Physiology|Large Intestine]]==

==[[Large Intestine Overview - Anatomy & Physiology|Large Intestine]]==

Undigested material spends a long time in the [[Caecum - Anatomy & Physiology|caecum]] and [[Large Intestine - Anatomy & Physiology|large intestine]] being digested by microbial fermentation, mainly cellulose (95% after 65 hours).  

Undigested material spends a long time in the [[Caecum - Anatomy & Physiology|caecum]] and [[Large Intestine - Anatomy & Physiology|large intestine]] undergoing microbial fermentation, mainly of cellulose (95% after 65 hours).  

In the hindgut of the horse; 75-85% of insoluble carbohydrates is digested, 15-30% of soluble carbohydrates and 30% of protein digestion. A lot of absorption of [[Volatile Fatty Acids|volatile fatty acids (VFAs)]] and water occurs in the large intestine which pass readily into the blood. Electrolytes are also absorbed in the large intestine; 95% of sodium and chloride and 75% of potassium and phosphate.

In the hindgut of the horse; 75-85% of insoluble carbohydrates is digested, 15-30% of soluble carbohydrates and 30% of protein is digested. A lot of absorption of [[Volatile Fatty Acids|volatile fatty acids (VFAs)]] and water occurs in the large intestine which pass readily into the blood. Electrolytes are also absorbed in the large intestine; 95% of sodium and chloride and 75% of potassium and phosphate.

To mix the contents of the large intestines, the taenia and circular muscle of the tunica muscularis contract. This also transports the ingesta through the large intestine and brings the products of fermentation in contact with the epithelium.

To mix the contents of the large intestines, the taenia and circular muscle of the tunica muscularis contract. This also transports the ingesta through the large intestine and brings the products of fermentation in contact with the epithelium.

The sequence of the limbs and flexures of the ascending colon is as follows; '''Right Ventral Colon''' ''(for those with an RVC bias remember, "the RVC comes first!")'', passes out of the caecocolic orifice on the right side of the abdomen and continues cranially to the xiphoid region; '''Sternal Flexure''', passes across the midline from right to left, '''Left Ventral Colon''', runs caudally on the left ventral abdominal floor; '''Pelvic Flexure''', turns dorsally just cranial to the pelvic inlet and then runs cranially to the diaphragm, '''Left Dorsal Colon''', runs cranially, parallel and dorsal to the left ventral colon; '''Diaphragmatic Flexure''', turns caudally at the diaphragm; '''Right Dorsal Colon''', continues caudally on the right. It is the shortest limb of the ascending colon.

The sequence of the limbs and flexures of the ascending colon is as follows; '''Right Ventral Colon''' ''(for those with an RVC bias remember, "the RVC comes first!")'', passes out of the caecocolic orifice on the right side of the abdomen and continues cranially to the xiphoid region; '''Sternal Flexure''', passes across the midline from right to left, '''Left Ventral Colon''', runs caudally on the left ventral abdominal floor; '''Pelvic Flexure''', turns dorsally just cranial to the pelvic inlet and then runs cranially to the diaphragm, '''Left Dorsal Colon''', runs cranially, parallel and dorsal to the left ventral colon; '''Diaphragmatic Flexure''', turns caudally at the diaphragm; '''Right Dorsal Colon''', continues caudally on the right. It is the shortest limb of the ascending colon.

The '''transverse colon''' continues on from the right dorsal colon as the right dorsal colon turns medially. The right dorsal colon is attached by a mesentery to the dorsal abdominal wall, the base of the [[Caecum - Anatomy & Physiology|caecum]], the root of the mesentry and the [[Pancreas - Anatomy & Physiology|pancreas]]. This anatomical arrangement of mesentery allows the left ascending colon to twist and is a common cause of [[:Category:Colic in Horses|colic]] ([[Large Colon Torsion - Horse|colonic torsion]]).  

The '''transverse colon''' continues on from the right dorsal colon as the right dorsal colon turns medially. The right dorsal colon is attached by a mesentery to the dorsal abdominal wall, the base of the [[Caecum - Anatomy & Physiology|caecum]], the root of the mesentery and the [[Pancreas - Anatomy & Physiology|pancreas]]. This anatomical arrangement of mesentery allows the left ascending colon to twist and is a common cause of [[:Category:Colic in Horses|colic]] ([[Large Colon Torsion - Horse|colonic torsion]]).  

The ventral parts of the ascending colon are attached to the dorsal parts by a short '''mesocolon'''. The mesocolon houses the blood vessels, nerves and lymphatics. In the ventral colon many important digestive and absorptive functions take place, whilst the dorsal colon is mainly responsible for transportation of ingesta. '''Taeniae''' are present. Different parts of the colon can be distinguished by the number of taeniae present:

The ventral parts of the ascending colon are attached to the dorsal parts by a short '''mesocolon'''. The mesocolon houses the blood vessels, nerves and lymphatics. In the ventral colon many important digestive and absorptive functions take place, whilst the dorsal colon is mainly responsible for transportation of ingesta. '''Taeniae''' are present. Different parts of the colon can be distinguished by the number of taeniae present: