Overview
The bovine small intestine (intestinum tenue) is very long and narrow. It receives acid contents from the abomasum and, after neutralising them with bile and pancreatic juice, digests and absorbs microbial protein, lipids and the carbohydrates that escaped ruminal fermentation. Because the rumen fills the left half, almost all the loops lie right of the median plane.
Parts
- Duodenum: the cranial part leaves the pylorus next to the liver and forms a sigmoid loop; the descending duodenum runs dorsally along the right flank to the caudal flexure, near the tuber coxae, and the ascending duodenum returns cranially, attached to the descending colon by the duodenocolic fold. The bile duct and, further caudally, the pancreatic duct open into the duodenum.
- Jejunum: the longest part; its many coils hang from the edge of the mesentery around the disc of the spiral colon and sit in the supraomental recess (recessus supraomentalis), the space enclosed laterally and ventrally by the greater omentum and open caudally. The jejunal lymph nodes form a long chain in the mesentery.
- Ileum: short final segment, attached to the caecum by the ileocaecal fold, opening at the junction of the caecum and colon through the ileal orifice.
Clinical relevance
- Intussusception: mostly of the jejunum, in calves and adults. It causes abdominal pain followed by scant faeces with mucus and dark blood; the distended loops can be palpated per rectum or seen by ultrasound on the right flank. It is resolved through a right flank laparotomy.
- Haemorrhagic bowel syndrome (jejunal haemorrhage syndrome): intraluminal bleeding with clots that obstruct the jejunum, in adult dairy cows; it has been linked to Clostridium perfringens type A. The prognosis is guarded.
- Paratuberculosis (Johne's disease): Mycobacterium avium subsp. paratuberculosis thickens and folds the ileal mucosa and causes chronic diarrhoea and weight loss in adults. The ileum and ileocaecal lymph nodes are sampled for diagnosis.
- Neonatal calf diarrhoea: enterotoxigenic Escherichia coli, rotavirus, coronavirus and Cryptosporidium parvum damage the villi; dehydration and acidosis are the main causes of death.
- Mesenteric volvulus: twisting of the loops around the root of the mesentery cuts off the blood supply and requires urgent surgery.