Abdomen of the pig

Regional Anatomy

The stomach of the pig is relatively large and when filled with food its greater curvature reaches a point on the abdominal floor midway between the xiphoid cartilage and the umbilicus. The long axis of the stomach is transverse. The pyloric extremity is in contact with the right lateral lobe of the liver, opposite to the middle of the thir­teenth intercostal space; the left end is ventral to the upper part of the left thirteenth rib and intercostal space.

The small intestine, in adult animals, is be­tween 15 and 20 m long. Its mesenteric portion is arranged in loops which lie above the colon and caecum, between the stomach and pelvis, mainly against the right wall, and on the posterior part of the floor of the abdomen. The support­ing mesentery is 15-20 cm in length. The large intestine, comprising the caecum, colon and rectum, varies from 4 to 5 m in length in adult pigs. The caecum forms a cylinder about 20-30 cm long and 8-10 cm in diameter, which is situated in contact with the upper and anterior part of the left abdominal wall from where it extends downwards, backwards and medially. The blind apex is in contact with the abdominal floor, near the midline somewhere between the umbilicus and the pelvic inlet. The colon, which at its origin is of similar diameter to the caecum, gradually reduces in size. The major portion of the colon is accommodated in the mesentery in three closely opposed double spiral coils which are situated on the abdominal floor, being rela­ted to the liver anteriorly, the caecum and small intestine posteriorly and the small intestine on the right. The terminal part of the colon, when it emerges from the spiral coils, forms a rather shallow, irregular U-tube by passing forwards on the right side of the dorsal part of the abdominal cavity where, at a point behind the stomach, it turns towards the left until, ventral to the pan­creas, it again turns backwards medially to the left kidney to reach the pelvic inlet where it continues as the rectum. The caecum has three rows of sacculations and three longitidunal muscular bands. The spiral colon has two series of sacculations and two muscular bands which do not reach the termination of the centrifugal part.

Clinical Examination of the Abdomen in the Pig

Clinical examination of the abdomen in the pig only occasionally provides rewarding results. Inspection readily reveals anatomical abnormali­ties such as umbilical or scrotal hernia (see Fig. 136, p. 149) which demand more detailed con­sideration when there is evidence suggesting in­testinal obstruction. The laboured abdominal type of breathing ('thumps'), which occurs in acute pneumonia or pulmonary oedema when lung efficiency is markedly reduced because of pulmonary engorgement and infiltration and the accumulation of exudate in the bronchioles and alveoli, is readily audible.

Palpation of the abdomen is rarely worth while except that in cases of severe abdominal pain a response is obtained readily at almost any point; otherwise, because of the thickness of the abdominal wall, localization of a pain focus is impossible. Except in very young pigs, identification of abdominal organs or recognition of abnormal swellings is not practicable. As a consequence, the differential diagnosis of diseases involving the abdominal digestive organs in the pig is based on a consideration of the evidence of disturbed function. In this connection, appe­tite, vomition and defaecation are important.

Lack of appetite in the pig is a feature of any acute illness and is not to be taken to indicate a primary digestive disturbance in all instances. In fact in mild or chronic diseases of the alimentary tract, appetite may be retained to a variable degree. Acute diseases which cause redistribution of body fluids or disturbance of tissue fluid balance increase the appetite for fluid; conse­quently if clean water is not available in these circumstances, the pig will drink any other fluid, including urine, that is available.

Gastritis, which may be acute or chronic in intensity, can be caused by irritant substances in the food, including inorganic arsenic, sodium fluoride, sodium chloride and iron, by eating straw bedding, by foreign bodies, ascarid worms (Ascaris suum), especially in young pigs, and Hyostrongylus rubidus, Ascarops slrongylina, Physocephalus sexalatus and Simondsia paradoxa in young pigs and lactating sows. Hyperaemia and infarction of the gastric mucosa occurs in acute colibacillosis, vibrionic dysentery, salmonellosis and swine erysipelas. Similar gastric lesions occur in swine fever, African swine fever and swine influenza. Gastritis is an important part of the pathological features of transmissible gastroenteritis. Similar, though less marked, gastritis occurs in vomiting and wasting disease.

In the pig, as in some other species of animals, acute gastritis causes increased motility, which is expressed clinically by vomiting of variable in­tensity. There is also an increase in peristalsis causing some abdominal pain. Appetite is always reduced, often completely absent, but thirst is excessive, so that affected pigs are almost continuously drinking whatever liquid is avail­able. Vomiting recurs repeatedly with strong retching movements; the vomitus contains mu­cus, sometimes blood, and is voided in small amounts.

Chronic gastritis gives rise to increased secre­tion of gastric mucus which delays digestion and gastric emptying; this may lead to chronic dila­tation of the stomach. The appetite is reduced or depraved, and vomiting, which is only occa­sional, usually occurs after feeding.

As is the case in other species, gastritis in the pig is frequently accompanied by enteritis of variable intensity. Parasitic gastritis in young pigs, caused by Hyostrongylus rubidus, Ascarops strongylina or Physocephalus sexalatus, produces a syndrome of anaemia, poor growth and diar­rhoea with marked thirst. In adult sows occasional deaths occur as the result of heavy infestations causing gastric ulceration and then severe haemorrhage, or perforation and peritonitis. A specific diagnosis is possible only by post mortem examination of the gastric mucosa with, in the case of H. rubidus, careful examination of a mucosal scraping mixed with water on a glass slide held over a black background.

The specific infective diseases, including swine erysipelas, swine fever, African swine fever and swine influenza, although they may cause vomit­ing to a variable extent, are associated with other clinical manifestations such as patchy cu­taneous erythema, febrile signs and in some instances convulsions.

Disturbances of intestinal motility in the pig, as is the case in other species of animals, are indicated by diarrhoea or constipation. Hyper-motility with ensuing diarrhoea is a feature of enteritis, which is often associated with gastritis in a number of specific diseases including colibacillosis, salmonellosis, vibrionic dysentery, transmissible gastroenteritis and vomiting and wasting disease. Systemic infectious diseases in which enteritis is a part of the pathological picture include, swine erysipelas, swine fever and African swine fever. In many of these conditions there is usually a preliminary period of intestinal hypermotility before diarrhoea becomes evident. The clinical syndrome is also associated with fever and other systemic manifestations in a number of these diseases. Other causes of enteri­tis are heavy infestations with Ascaris suum, coccidia including Eimeria debliecki, Eim. escabra and Eim. perminuta, irritant foods such as frozen roots and chemical irritants such as arsenic, sodium fluoride or iron in excessive amounts.

Enteric colibacillosis of young pigs usually occurs in young animals of 8-18 weeks of age, although occasional cases are seen in piglets 24-72 hours old, in which the infection is gener­ally septicaemic in character. The disease is caused by serotypes of haemolytic Escherichia coli similar to those causing gut oedema. The clinical features of the enteric syndrome include depression, anorexia, fever (40-5°C, 105°F) and diarrhoea. Dysentery is not a feature. The diag­nosis depends upon appreciation of the clinical signs, history, post mortem findings of moderate to severe enteritis and isolation of haemolytic E. coli in almost pure culture from the caecum and colon or from rectal swabs in living affected pigs. Final assessment of the significance of any coliform bacterium isolated necessitates the ap­plication of serotyping methods.

Salmonellosis (paratyphoid) in pigs is generally a much more acute disease than colibacillosis. It is caused by Salmonella choleraesuis and Salm. typhimurium. Clinical disease appears, however, to require the operation of a predisposing factor, or factors, such as sudden change in feeding, dosing with an anthelmintic, dietary deficiency, etc. In the acute enteric form of salmonellosis there is a marked, febrile reaction, 40-41 °C (104-106°F), persistent watery diarrhoea, some­times dysentery and, occasionally, tenesmus. Less severe cases give rise to a syndrome of rather persistent diarrhoea, with intermittent febrile periods and, eventually, marked emaciation. The diagnosis of salmonellosis is a matter of some difficulty in living pigs because a number of other diseases have similar clinical manifesta­tions. The clinical and pathological findings for the enteric syndrome should direct attention to the need for bacteriological investigation. For this purpose samples of faeces (not less than 20 g) from living animals, or intestinal contents and specimens of spleen, mesenteric lymph node, liver and gall-bladder from carcases should be selected. Selective media are essential for primary isolation, and serological methods for specific identification of salmonellae.

Vibrionic dysentery of pigs is generally con­sidered to be caused by Vibrio coli, although the possibility of there being some other primary factor has been postulated because of the diffi­culty of reproducing the disease with pure cul­tures of V. coli. Predisposing factors, such as fatigue and exhaustion arising during transporta­tion, appear to have a significant influence on the development of clinical disease. The main clin­ical features consist of the sudden onset of severe diarrhoea with anorexia and mild febrile signs. The faeces are very fluid, contain mucus and are passed in an uninterrupted stream without physi­cal effort. Initially they are yellow in colour but within 24-48 hours they become black or blood-tinged or whole clots of blood may be present. Affected animals are depressed and dehydration is severe. The morbidity and mortality rates may be high; acutely affected pigs may die within 24 hours but death may be delayed for up to 4 days. Apparently recovered pigs may relapse and die later. Occasionally the infection may be responsible for chronic persistent diarrhoea. Diagnosis is based on recognition of the severity of the diarrhoea associated with dysentery, and the absence of pulmonary and nervous system involvement which exists in some cases of sal­monellosis. Vibrio coli can be demonstrated in stained smears from the mucosa of the colon.

Transmissible gastroenteritis of pigs is caused by a host-specific virus. The initial clinical signs consist of the sudden onset of vomiting and diarrhoea; appetite, at least in young sucking pigs, is sometimes retained until shortly before death. The faeces are yellow-green in colour, watery in consistency and profuse in amount. Depression and dehydration are pronounced and weakness and emaciation precede death which may occur on the second to fifth day. The mor­tality rate is highest in very young pigs. The history and clinical signs form the basis for a presumptive diagnosis but specific confirmation depends upon the results of serological and bio­logical tests.

Coccidiosis is a disease of young pigs. The initial sign of active infection is diarrhoea which may be followed by constipation. The appear­ance of blood in the faeces is exceptional. Other signs include anorexia, dehydration and emacia­tion. The disease is diagnosed by correlating the history and clinical signs with the results of a faecal examination for oocysts. Specific identi­fication is rather difficult and usually not neces­sary.

The significance of the protozoan unicellular ciliate, Balantidium coli, in relation to enteritis in the pig is not entirely clear. The infection rate varies from 20 to 100 % but in cases of clinical disease bacteria such as streptococci or E. coli are frequently present. The disease affects pigs of all ages and is usually most severe in advanced pork and bacon pigs. The main signs are inter­mittent diarrhoea, anorexia, depression and loss of weight. Stunting is usual in young pigs. Diag­nosis depends upon identification of the tropho-zoites or cysts in the faeces or in smears of mucosal scrapings from the haemorrhagic colon.

Vomiting and wasting disease of sucking pigs, which bears some resemblance to transmissible gastroenteritis, may be associated with diarrhoea in the older age range of the affected piglets. In this condition the diarrhoea is not severe and is overshadowed by other signs, particularly vomition.

Constipation is a sign of intestinal hypomotility, and is the result of the faecal contents of the gut becoming excessively dry, or of obstruc­tion. Excessively dry faeces occur when there is insufficient water available with a dry-feeding system, when the fibre content of the diet is insufficient to ensure adequate bulk, and in sows in advanced pregnancy, in which lack of exercise is an important predisposing factor. The most important cause of intestinal obstruction is im-paction with either inspissated faeces or large numbers of Ascaris suum. The clinical signs consist of failure to pass faeces, lack of appetite, slight to vigorous straining and depression. When restlessness, exhibited by lying down and standing up again repeated almost continuously and accompanied by vomiting with eructation of gas, is associated with constipation, then intesti­nal obstruction, caused by torsion, intussuscep­tion or strangulation, or peritonitis should be suspected. Intussusception more usually occurs in young pigs and frequently results from feeding unsuitable diets or from the presence of ascarid worms in the small intestine. In addition to the signs of abdominal pain there is the passage of blood-stained mucus and faeces in small amounts and tenesmus, which may lead to prolapse of the rectal mucosa.

Intestinal torsion is a relatively rare condition occurring in young pigs as a complication of hernial strangulation or of acute peritonitis with adhesions between neighbouring segments of intestine. Strangulation usually affects a loop of intestine in a hernial sac when the former be­comes overfilled with food and is unable to escape from the sac. The majority of such cases are associated with an umbilical hernia, only exceptional instances occurring with scrotal or diaphragmatic hernia. In addition to signs indi­cating acute abdominal pain, local signs are recognizable consisting of inflammation of vary­ing intensity in the skin over the hernial sac, and pain on palpation of the hernial contents which are somewhat firm and cannot be reduced.

Reduced intestinal motility also occurs, along with other signs in oesophagogastric ulceration and diverticulitis and ileitis in pigs. In the former the main signs are pallor due to massive haemor­rhage into the stomach, anorexia and black pasty faeces, changing to mucus-covered pellets which are passed in small amounts. The con­dition is identified by finding ulcers confined to the oesophageal zone of the stomach at post mortem examination. The latter disease is usually associated with signs of acute peritonitis due to ulceration and, sometimes, perforation of the ileum. Post mortem examination reveals gross thickening of the wall of the ileum which may be perforated, with in this instance diffuse peri­tonitis.

Prolapse of the rectal mucosa occurs as the result of inflammation of the rectum (proctitis) which may arise as a stage of progression in enteritis, or follows prolonged and repeated tenesmus in severe constipation.