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| − | <big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big>
| + | #redirect[[Alimentary System - Horse Anatomy]] |
| − | <big><center>[[Hindgut Fermenters - Anatomy & Physiology|'''BACK TO HINDGUT FERMENTERS- ANATOMY & PHYSIOLOGY''']]</center></big>
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| − | ==Introduction==
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| − | The typical horse's diet consists of 7-12% protein and 4% fat, the remainder being made up of carbohydrate. A high proportion of the 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.
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| − | Undigested material spends a long time in the caecum and large intestine being digested by microbial fermentation, mainly cellulose (95% after 65 hours).
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| − | In the hindgut of the horse,
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| − | *75-85% of insoluble carbohydrates is digested.
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| − | *15-30% of soluble carbohydrates.
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| − | *30% of protein digestion.
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| − | ===Development===
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| − | The ascending colon expands '''cranially''' (compared to ox, where it expands caudally) around the root of the mesentry on the left side of the mesentry.
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| − | ==[[Small Intestine - Anatomy & Physiology|Small Intestine]]==
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| − | *Arrangement is similar to that of the dog's small intestine, but the position of the jejunum is influenced by the large ascending colon and caecum.
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| − | **The jejunum is restricted to the left dorsal part of the abdomen.
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| − | *Transit time of food in the small intestine is quite rapid.
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| − | **25% of a liquid marker has reached the caecum within 1.5 hours.
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| − | **Most ingesta reaches the large intestine within 3 hours after intake.
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| − | *70-80% of protein is digested.
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| − | *70%+ of starch is digested by '''enzymes'''.
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| − | ==Caecum==
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| − | *On the right side of the abdomen.
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| − | *Very large, roughly 1m in length with a 30L capacity.
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| − | *Consists of a base, body and apex (blind ending).
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| − | *The base lies in the right dorsal part of the abdomen in contact with the abdominal roof.
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| − | *Apex lies on the ventral abdominal wall, and terminates at the level of the xiphoid cartilage.
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| − | *Exists at the junction with the ileum and colon.
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| − | **The '''caecocolic orifice''' is where the caecum opens into the ascending colon. This exists as a transverse slit formed by a constriction of the ascending colon.
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| − | **The ileum opens into the caecum at the '''ileal papilla'''. This is a small projection into the caecum housing the ileal sphincter and venous plexus that, together, control the ileal orifice.
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| − | *Taenia are present.
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| − | **Taenia are formed by concentration of the ''longitudinal'' muscle layer.
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| − | **Between the taenia are sacculations, or haustra.
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| − | **Haustra appear as folds on the interior surface.
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| − | ***There are '''four''' taenia over the caecum: -dorsal - ventral - lateral -medial.
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| − | ***The ''dorsal'' taenia provides the attachment site for the ileocaecal fold, which joins the caecum to the ileum.
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| − | ***The ''lateral'' taenia provides the attachment site for the caecocolic fold, which joins the caecum to the ascending colon.
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| − | ***The ''ventral'' taenia is free.
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| − | ***The ''medial'' and ''lateral'' taenia are where the caecal vessels and lymph nodes are located.
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| − | *Ingesta is regularly transported from the ileum to the caecum, this movement can be heard upon auscultation of the right dorsal quadrant of the caudal abdomen.
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| − | **Ausculatation of this area is carried out in assesment of colic.
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| − | *In the horse, the caecum is responsible for the digestion of complex carbohydrates such as cellulose.
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| − | ==Colon==
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| − | ===Ascending colon===
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| − | *The ascending colon is very large and takes up most of the ventral abdomen.
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| − | *It is the shape of a double "U", where one "U" is on top of the other.
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| − | *There are four limbs that lie parallel to each other, and three flexures that change these direction of the limbs.
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| − | *Sequence of the limbs and flexures of the ascending colon:
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| − | **Right Ventral Colon ''(for those with an RVC bias remember, "the RVC comes first!")''
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| − | ***Passes out of the caecocolic orifice on the right side of the abdomen and continues cranially to the xiphoid region.
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| − | **''Sternal Flexure''
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| − | ***Passes across the midline from right to left.
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| − | **Left Ventral Colon
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| − | ***Runs caudally on the left ventral abdominal floor.
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| − | **''Pelvic Flexure''
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| − | ***Turns dorsally just cranial to the pelvic inlet and then runs cranially to the diaphragm.
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| − | **Left Dorsal Colon
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| − | ***Runs cranially, parallel and dorsal to the left ventral colon.
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| − | **''Diaphragmatic Flexure''
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| − | ***Turns caudally at the diaphragm.
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| − | **Right Dorsal Colon
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| − | ***Continues caudally on the right. It is the shortest limb of the ascending colon.
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| − | *The '''transverse colon''' continues on from the right dorsal colon as the right dorsal colon turns medially.
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| − | *The right dorsal colon is attached by a mesentry to the dorsal abdominal wall, the base of the caecum, the root of the mesentry and the pancreas.
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| − | **This anatomical arrangement of mesentry allows the left ascending colon to twist and is a common cause of colic (colonic torsion).
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| − | *The ventral parts of the ascending colon are attached to the dorsal parts by a short mesocolon.
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| − | **The mesocolon houses the blood vessels, nerves and lymphatics.
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| − | *In the ventral colon many important digestive and absorptive functions take place, whilst the dorsal colon is mainly responsible for transportation of ingesta.
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| − | *Taenia are present.
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| − | **Different parts of the colon can be distinguished by the number of taenia present:
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| − | ***The right and left ventral colon and the sternal flexure have '''four''' taenia.
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| − | ***The left dorsal colon and pelvic flexure have '''one''' taenia.
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| − | ***The right dorsal colon and diaphragmatic flexure have '''three''' taenia.
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| − | ===Transverse Colon===
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| − | *Short
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| − | *Passes from across the midline from right to left. It passes cranial to the root of the mesentry
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| − | *The transverse colon has '''two''' taenia.
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| − | *Turns caudally to become the descending colon at the level of the left kidney.
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| − | ===Descending Colon===
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| − | *Between 2-4m long.
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| − | *Suspended by a long mesentry; ''mesocolon descendens''.
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| − | *The descending colon has '''two''' taenia.
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| − | **Between the two taenia are distinct sacculations that house the faecal balls.
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| − | ==Rectal Palpation==
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