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A four-year old pedigree Holstein was presented with reduced appetite, a sudden decrease in milk yield, signs of colic and reduced faecal production. The cow, who was in her second lactation and had calved 3 months prior, displayed signs of pain but no signs of shock. Vital signs were measured and showed no abnormalities: heart rate (70bpm), rectal temperature (38.5Â°C) and mucous membranes were all normal. A small swelling was observed in the right paralumbar fossa and tympanitic resonance was found on auscultation of the right side of the abdomen. A rectal examination was carried out and a blind-ending structure with a large diameter was found pointing towards the right paralumbar fossa and no faeces were found in the rectum, only mucoid material. An initial diagnosis was made of; caecal dilation, torsion or volvulus (Green, M.J. & Husband, J.A., 1996).
General anatomy of the bovine intestinal tract
Figure 1 -Right lateral view of the bovine intestinal tract.
1. Duodenum 2. Jejunum 3. Jejunal lymph nodes 4.Illium 5. Caecum 6. Illiocaecal fold 7. Proximal loop ascending colon 8. Centripetal turns of spiral colon 9. Centrifugal turns of spiral colon 10. Transverse colon 11. Descending colon 12. Rectum After leaving the abomasum through the pyloric sphincter, food moves into the small intestine which can be 27-49m in length. Any remaining fats, proteins or soluble carbohydrates are broken down here. The first region is the duodenum, which begins on the right in a ventral position (Budras et al., 2011) before moving cranially in the direction of the liver (Dyce et al., 2010). The cranial aspect then turns caudally at the caudal flexure and is known as the descending duodenum (Budras et al., 2011) which progresses until approximately the level of the tuber coxae (Dyce et al., 2010). The descending duodenum, along with the right lobe of the pancreas, is encapsulated within the mesoduodenum (Budras et al., 2011). Once at the level of the tuber coxae, the caudal flexure results in the duodenum moving cranially to form the ascending duodenum, which returns towards the liver along the left lateral side of the cranial mesenteric artery.
At the point where the mesoduodenum begins to lengthen, the small intestine becomes the jejunum. The jejunum has a distinct coiled appearance and follows a basic pathway ventrally, caudally and then dorsally in the direction of the large intestine. The caecum's attachment to the small intestine demarks where the jejunum becomes the ileum (Dyce et al., 2010). The caecum attaches to the colon at the caecocolic orifice (Budras et al., 2011) where initially there is no change in diameter. The colon begins as the ascending colon which has a coiled and narrowed structure, turning ventrally with two centripetal and two centrifugal turns which directs it towards the edges of the mesentery, where it becomes the transverse colon (Dyce et al., 2010). This portion of the colon is generally rather short in comparison to the overall length of 7-9.5m. The transverse colon then crosses the midline across the mesenteric artery before becoming the descending colon, which travels towards the pelvic inlet. Here the mesenteries are short but lengthen at the level of the sacrum. The descending colon then becomes the rectum. Both of these regions are supplied by the caudal mesenteric artery (Frandson et al., 2009). Additionally, the cranial mesenteric artery supplies the midgut; from the caudal duodenum to the ascending colon, whilst the coeliac artery supplies the cranial duodenum (Dyce et al., 2010).
Anatomy of the bovine caecum
Diagram of the bovine caecum and incision sites for this case. The caecum occurs at the junction between the ileum and the colon. It is a blind ended diverticulum of the large intestine and varies in size and shape between species. It is of more importance in hindgut fermenters, such as the horse, as it is the site of a large amount of microbial fermentation (Dyce et al., 2010). In cattle the caecum is relatively large and is found on the right side of the abdomen. The apex of the caecum points caudally (Dyce et al., 2010).C:\Users\Emmaa\Downloads\caecum (1).jpg
The caecum receives its blood supply from the cranial mesenteric artery and is connected to the ileum by the ileocaecal fold, a minor fold of peritoneum forming a short mesentery. It has two orifices; iliocaecal and caecocolic. These are both guarded by sphincters (Carrington et al., 2012).
Developmental anatomy of the gastrointestinal tract in ruminants
Development of the gastrointestinal tract begins with a gut tube formed of endoderm. The tube undergoes cranial, caudal and lateral folding and incorporation of the primitive yolk sac. The cranial fold forms the foregut, the caudal fold the midgut, and the lateral fold the hindgut. These structures are enveloped in splanchnic mesoderm, from which the dorsal and ventral mesenteries are formed. Via these mesenteries the developing gut is attached to the abdominal wall. The foregut forms the stomach, the cranial part of the duodenum, the Liver and the Pancreas. The midgut forms the caudal part of the duodenum, jejunum, ileum, caecum, ascending colon and part of the transverse colon. The hindgut forms the remainder of the transverse colon, descending colon and the rectum. These structures form through a series of elongations and rotations. In the ruminant, there are species specific stages to the embryological development of the GI tract. The caecum increases in size, and the ascending colon lengthens, forming a loop attached to a section of dorsal mesentery, known as the mesocolon. The loop then forms a coil, this coiling of the ascending colon happens between the 2nd -4th month of gestation (McGeady et al., 2006).
Anatomy of the viscera and mesentery surrounding the caecum and how it caused certain rotations in the clinical case
Diagram showing how the restricted size and shape of the ileocaecal fold caused the caecum to bend as it dilated. Located on the right side of the mesentery, cranial to the extensive loops of jejunum (Pasquini et al., 2007), the bovine caecum described in the clinical case initially rotated away from the mesentery in a clockwise and cranial direction (Green, M.J. & Husband, J.A., 1996). However, the iliocaecal fold restricts the movement of the caecum, preventing further clockwise rotation. The limited size and length of the iliocaecal fold and its attachment to the caecum causes the originally straight caecum to bend as it dilates into a more curved shape, as shown in Figure 3. Containing large amounts of heavy content causes the caecum to sink ventrally (Dyce et al., 1996). The location of the proximal jejunum and other surrounding viscera allows the contorted and very dilated caecum to kink further into a sigmoid shape (Green, M.J. & Husband, J.A., 1996) to occupy the limited available space within the caudal abdomen. Bovine caecal dilation presentations can vary; studies of other cattle requiring surgery have shown that the position of the caecum when displaced is due to many factors, including a diet with a high concentrate to roughage ratio (Braun et al., 2012) (Scott et al., 2011).
Anatomy and pathology of the volvulus and its surgical remedy
In the clinical case, rotation and torsion of the caecum was caused by an increase in volatile fatty acids, which led to excessive dilation. This dilation caused the distortions and rotations described previously, the consequence of which was a build-up of caecal content and eventual impaction of the caecum due to a significantly reduced lumen size (Green, M.J. & Husband, J.A., 1996).
After the impaction of the caecum was removed, the caecal tissue left had been without adequate blood supply for too long prior to the operation, causing the tension in the smooth muscle of the gut to be reduced so that the caecum lost its contractility. Therefore the caecum was removed by making an incision at the distal ileum and the proximal colon. However, due to the colon's short mesentery, attached to the left dorsal body wall making it difficult to expose and suture the junction left between the distal ileum and the proximal colon ventrally (Green, M.J. & Husband, J.A., 1996).
In this case, the cow was diagnosed with sigmoid caecal volvulus and a total typhlectomy was carried out. Gastrointestinal operations are usually carried out under general anaesthesia but this case was an exception. Cattle can function well without a caecum as the majority of fermentation occurs in the rumen. The cow recovered quickly and returned to the dairy herd one month later, where its faecal output was normal and had a milk yield of approximately 25 litres (Green, M.J. & Husband, J.A., 1996).