Age affected: Growers/ finishers.
Causes: Sequel to prolapsed rectum; blood vessel damage from bacterial infection.
Effects: Abdomen enlargement, inappetence, ribbon-like diarrhoea, death.
Rectal stricture often follows untreated rectal prolapse in which the prolapse has sloughed and may also follow enteritis in which excoriation of the rectal mucosa and the associated mucocutaneous junction is a feature. This area has a blood supply from the posterior haemorrhoidal artery (from inside the pelvic cavity) and from the perineal arteries (around the anus) but a poorly-vascularised zone exists at the junction of the two blood supplies. Any mucosal ulceration or arteriolar thrombosis here causes damage to the mucosa which heals by scarring.
In male pigs, the presence of the retractor penis muscle lying across the rectum at this point may exacerbate changes. The circulatory and inflammatory changes are commonly due to salmonella infections. In some cases the syndrome follows the use of an antimicrobial such a tylosin and it has been said to result from overgrowth by Candida spp. and other yeasts which may be isolated from affected colons. Another site at the brim of the pubis may be inflamed in the chronic stage of enteric disease.
The condition often develops within 10 days of a dietary change and is often preceded by stickiness and erythema at the mucocutaneous junction, accompanied by a marked reluctance to defaecate.
Mode of transmission
The condition itself is not transmissible. The predisposing factors may, however, be infectious, as in the case of salmonellosis. The exact mechanism by which the association with antimicrobial treatment is mediated is not known.
Affected pigs become dull, depressed, lose their appetite and cease to grow. They become hairy and the skin is dull, flaky and may be yellowish. They tend to stand in corners away from the group.
The abdomen becomes grossly distended and the outline of the swollen colon may be seen through the wall. The anus may remain blocked until the animal dies or break down to allow a dribble of bubbling faeces to leak out. In some cases, the partially blocked rectum allows the passage of soft ribbon-like motions. Pigs which have re-established a patent anus eat and gain weight, however, when two successive weights one week apart show no growth, it is likely that the stricture has re-established.
The presence of a pig aged 5 weeks or more with a distended abdomen, dull skin, depressed and standing in the corner of a pen suggests that it has rectal stricture and the diagnosis can be confirmed by the insertion of a thermometer or gloved finger into the rectum when an obstruction will be met 2-4 cm or more in to the rectum. When faeces are present, the stricture may be incomplete.
The carcass is thin, the abdomen is distended, the skin is often dirty with surface flakes of skin. The body wall should be opened with care as the distended large intestine is thin-walled and pressed extremely tightly against it. The large intestine should not be opened until examination of the pelvic structures and thorax is complete. Careful dissection of the pubic symphysis and exposure of the rectum in the pelvic canal will confirm the existence and site of the stricture. This normally appears as a bulge continuing the line of the swollen colon and rectum, contracting to a narrow band of tissue and then reaching the anus as a normal empty rectum.
There may be abscessation of the stricture. The chest cavity is compressed and the lungs are much reduced in size by the raised intra abdominal pressure. The large intestine is filled with gas and the contents vary between sloppy and firm. When rinsed, the mucosa may be found to be normal in appearance.
Treatment and prevention
Affected pigs are unlikely to recover without surgery and should be killed humanely. Insertion of a probe through the stricture rarely resolves the stricture. It is technically possible for a veterinary surgeon to exteriorise the constructed rectum dorsal to the anus while the pig is anaesthetised.
The rectum can be cut proximal to the obstruction and sewn in to the perineum to form a new anus. A rubber sleeve can be used to exteriorise the caecum or mid-colon in a colostomy. Surgically treated pigs may grow rapidly to gain market weight or may develop fresh strictures. Animals which fail to gain weight for the first three weeks post-operation should be destroyed.
The syndrome may be reduced in incidence by the prompt repair of rectal prolapses and the treatment of outbreaks of chronic diarrhoea in animals at risk. Antimicrobials capable of treating salmonella and Yersinia infections have been found to eliminate the early inflammatory lesions of the rectal wall and to prevent the disease.