Large intestine

The large intestine in domestic animals is the final segment of the digestive tract, composed of the cecum, colon, and rectum. It is primarily responsible for water and electrolyte absorption, fermentation of undigested material (especially in herbivores), and formation and storage of feces. Its structure and function vary among species, with hindgut fermenters like horses having a highly developed large intestine to support microbial digestion.

The anatomy of the large intestine in domestic animals varies among species but generally includes the cecum, colon, rectum and anal canal.

Species Variations

• Ruminants (e.g., cattle, sheep):

  • The jejunum can be extremely long, and the ileum is often difficult to distinguish grossly.

  • The duodenum has a sigmoid flexure (sigmoid ansa) and is closely associated with the liver and pancreas.

• Horses:

  • Long jejunum (can be 20 meters), which makes it prone to displacement or torsion (colic).

  • The ileum is relatively short and empties into the large cecum.

• Pigs:

  • Have a well-developed duodenal loop and relatively compact intestinal loops.

  • Peyer’s patches are especially large and numerous in the ileum.

• Dogs and Cats:

  • Classic segmentation is visible; the small intestine is highly mobile and prone to obstruction or volvulus.

Blood Supply and Innervation

• Arterial Supply: Primarily via branches of the cranial mesenteric artery, with rich anastomoses.

• Venous Drainage: Via the superior mesenteric vein and portal vein to the liver.

• Innervation: Autonomic nerves via the mesenteric plexus regulate motility and secretion.

Histological Layers (all segments)

From innermost to outermost:

• Mucosa: With villi and intestinal glands (crypts of Lieberkühn)

• Submucosa: Contains blood vessels, lymphatics, and nerve plexuses

• Muscularis externa: Inner circular and outer longitudinal smooth muscle layers

• Serosa: A thin connective tissue layer covered by mesothelium