Colitis, a Specific Cause of Diarrhoea

Disease of Alimentary System


The colon in the lower bowel is primarily concerned with reabsorption of water as the products of digestion move down the alimentary tract. Any influence which leaves water within the bowel will contribute to the water content of the dog’s motions, which can vary from slightly wet faeces to frank diarrhoea if the colon becomes inflamed. Any blood present is usually fresh, staining the motions red, and often there is straining, discomfort and a degree of pain. Motions may contain mucus, with little evidence of unabsorbed fat. Veterinary examination is necessary to establish the several clinical conditions. Boxers appear to have a predisposition to two types of ulcerative colitis: Histiocytic Ulcerative Colitis, which does not respond well to treatment; and Idiopathic Ulcerative Colitis, which may recover with appropriate treatment. Dietary treatment has little effect on lower bowel conditions; the underlying cause for colitis must be established.
Colitis, inflammation of the large intestine, is responsible for half of all cases of recurrent or Persistent diarrhoea in the dog. Inflammation of the colon lining prevents residual vvater from being absorbed efficiently, thus creating this common problem. Here Dr Bush discusses the characteristics and causes of the disorder, details the treatment and relates vvhich dogs are especially prone to the condition. DIARRHOEA is a fairly common problem in the dog and at times it may persist indefinitely or recur frequently. The term is usually taken to mean the passage of motions which are softer (i.e. more liquid) than usual, but it can also be used to refer to an increased frequency of defaecation. Diarrhoea is, of course, not a disorder in its own right but merely a sign which can arise for a number of different reasons. It is this diversity of causes which sometimes makes successful teatment very difficult. It is often not appreciated that throughout most of their length the contents of the intestines have a very liquid consistency. This is because as food passes along the digestive tract a large volume of water is added in the form of the digestive juices – approximately 1 pint for every 12 pounds of a dog’s weight. In normal animals, the majority of this water is subsequently absorbed, together with the digested foodstuffs, through the wall of the small intestine. Even so, as the food residues pass beyond the small intestine there is still sufficient water present for them to remain semi-liquid; most of this is absorbed as the residues traverse the terminal part of the digestive tract – the large intestine, particularly the colon. Most cases of diarrhoea involve the small intestine. Anything which irritates and inflames that organ will increase the motility of the muscle in its wall so that the intestinal contents are passed through, and out, so rapidly that it is not possible for the usual amount of water to be removed, In those cases where there is a failure to adequately digest, or absorb, foodstuffs in the small intestine, a different mechanism operates. The foodstuffs which remain behind in the intestine attract water to themselves preventing it being absorbed, and this inevitably results in the passage of motions having a much higher water content than usual. This is what happens in exocrine pancreatic insufficiency (due to a deficiency of digestive enzymes from the pancreas) and in many types of malabsorption (e g. bacterial overgrowth in German Shepherd Dogs and wheak sensitivity in Irish Setters).
.          However, in other cases the small intestine is not involved and it is inflammation of the large intestine which is primarily responsible for the diarrhoea. This is because the inflammation of the lining cells prevents them absorbing the residual water efficiently. These are referred to as cases of colitis (strictly meaning inflammation of the colon, although usually the rectum is also involved). It has been held that a half of all cases of recurrent or persistent diarrhoea are of this type.

Characteristics of Colitis

As well as the presence of diarrhoea, dogs with colitis generally how a number of other signs which characterise the disorder .
1. The passage of abnormal amounts of mucus, looking like jelly or egg white. This is produ- ced as a protective measure in response to the Inflammation. !n milder cases of colitis, the animals may pass formed stools which every few days appear completely coated with mucus resembling a sausage skin or plastic bag.
2. The passage of red blood in, or on, the faeces. This sign is not always present and in mild colitis it may never appear. On the other hand, some severe cases suffer from dysentry: the passage of large amounts of blood-stained mucus and totally liquid faeces.
3. More frequent deflection. Instead of the usual 2 or 3 bowel movements per day, most dogs with colitis defaecate at least 5 times. This is because inflammation of the nerve endings in the wall of the rectum continually gives the feeling of a full bowel and so stimulates the desire to pass a motion.
4. Undue straining. Even after completely emptying the rectum. the sensation of “fullness” persists and it is common for animals to make several further attempts to pass motions. Usually these attempts, which may be obviously painful to the dog, result only in srnall amounts of mucoid material being passed. if indeed there is anything at all.
5. The recurrent nature of the condition. Cases of chronic (i. e. long-standing) colitis usually show an intensification of signs at intervals ranging from several months to a few weeks or days. Such “attacks” generally resolve whether or not any treatment is given, but if untreated, or the treatment is not specific for colitis, “attacks” tend to reappear at shorter and shorter intervals, until eventually the signs are present continuously.
6. Vomiting. This is another variable sign. Many dogs with colitis never show it but in around one-third it accompanies “attacks”, often beginning 24 hours before the abnormalities of defaecation appear. The existence of vomiting does not indicate that there is any damage to the stomach. It occurs because the irritated nerve endings in the colon trigger off impulses which pass to the area known as the vomiting centre in the brain and which in turn initiates the process of vomiting. (in this regard it is similar to motion sickness which also arises without there being any damage to the stomach).
7. A normal appetite. The appetite is not increased, as it is when there are defects of digestion or absorption in the small intestine, and unless the animal shows a temporary reluctance to eat during a severe episode, its appetite remains normal.
8. Virtually no weight loss. In general, the animal’s body weight is maintained because the digestion and absorption of foodstuffs has already taken place in the small intestine. In contrast, small intestinal diseases are characterised by a fall in weight. If there is any weight loss in colitis, and it is seldom severe, it usually results from the inappetence which accompanies a severe “attack” or the votmiting back of meals.


Sometimes the colitis forms part of a generalised disorder, i. e. one which involves several parts of the body simultaneously. This most commonly occurs where there is an accumulation of protein waste-products (known as uraemia) due to kidney damage, but colitis has also been seen in such conditions as canine distemper and mercury poisoning. However, in most cases of colitis the inflammation is confined to the large bowel and no other organ is involved. Some of these cases are known to follow infection with particular bacteria, fungi or parasites, and probably the most common infectious cause (certainly in the U.S.A.) is a heavy infection with whip- worms. But far more often, no obvious reason for the colitis can be discovered so that the best term to describe majority of cases is idiopathic chronic colitis, meaning that they have no known cause. There are, of course, a number of theories as to why they have arisen, including a reaction to viruses, abnormal immunity (particularly dietary allergy), psychological upsets and a genetic predisposition. Currently it seems probable that more than one cause is involved in a single individual.

Colitis Appears to be Breed Predisposed

There certainly appears to be good reason for believing that an animals genetic make-up plays a part because colitis has been observed to occur more frequently in certain breeds than others. The highest incidence is in the Collie breeds (especially the Rough Collie and Shetland Sheepdog) followed by the Spaniels (and in particular the King Charles and Cavalier King Charles). the Golden Retriever and the German Shepherd Dog. In addition, colitis is often the reason for persistent or recurrent diarrhoea in the smaller breeds such as the Miniature Long-Haired Dachshund, because in these breeds malabsorption as a cause of long-standing diarrhoea rarely occurs. However, it seems probable that colitis may develop in any breed. Variants of the basic disorder have been recognised and the best known of these is histiocytic ulcerative colitis. As the name indicates, featuras of this disease are the presence of cells called histioytes in the lining of the intestine and the development of ulcers, in the bowel wall. This type of coiitis, which may prove less responsive to treatment, seems confined to the Boxer and the related breed the French Bulldog.

Young Dogs are more Prone to the Disorder

Colitis can arise at any age from a few months old to 14 years or mote, but the majority of cases occur in young adults before the age of 5 years, with a peak between 1 and 2 years old. There is a possibility that males are slightly more at risk than females. Affected dogs include a number of incurable trasheaters and animals of an excitable or neurotic temperament. Indeed, some owners are able to definitely associate occasions where there has been stress or excitement with the onset or recurrence of those signs mentioned earlier. Although certain complicating features such as anaemia or a low protein level in the blood can be detected by routine laboratory tests, there, is no specific test for colitis. If confirmation of the diagnosis is required,this may be obtained by specialised radiography, viewing the lining of the colon through an endoscope inserted via the anus or examining minute snippets of the bowel lining (i. e, biopsies) removed with an instrument inserted by the same route. As would be expected, abnormal findings obtained by these methods are most common in severe cases. This idiopathic chronic colitis of the dog has a number of features in common with the two important inflammatory disorders of the colon in humans, ulcerative colitis and Crohn’s disease of the colon (granulomatous colitis), and generally treatment is along the same lines. On occasion, the term “irritable bowel syndrome” has been applied to colitis in the dog. but in humans this disorder has certain well established features, such as constipation, which seldom appear in the dog and at present it seems preferable not to apply this term to canine cases.


Unless there is some known cause (e.g. whipworms, or kidney failure) requiring specific treatment, the keystone of therapy, as in human patients, is the use of the drug sulphasalazine’ trade name “Salazopyrin”. Once the underlying inflammation of the large bowel has subsided, this drug is very effective in preventing further “flare-ups”. Unfortunately, when used alone in severe cases, it is seldom able to ‘ damp down” the inflammation sufficiently to bring the condition under control. For this reason, at the start of treatment sulphasalazine is often combined with a corticosteroid (usualy prednisolone), which is more effective at reducing inflammation. The corticosteroid can then be gradually phased out over a period of a month or so. (incidentally, if cor- ticosteroids are used alone they are much less effective at preventing subsequent relapses.) Some dogs show a permanent cure after a few weeks therapy but many severe cases of colitis show a recurrence of signs four to six weeks after stopping treatment and in these the indefinite use of sulphasalazine appears advisable. A very few animals show signs of alimentary disturbance initially; a more important long-term side effect is “dry eye” in a small proportion of dogs. Other drugs have also been used in treatment though in general they have proved to be less consistently effective. In both man and the dog there have been conflicting recommendations for both low- fibre and high-fibre diets, the latter achieved by the addition of bran. Whilst some individuals are significantly improved by one or the other, the impression is that in the majority of cases neither diet is superior, or indeed necessary. In general. a balanced diet which is relatively bland (avoiding excessive salt or spices, as in salami or curry) has proved perfectly adequate. Care should be taken, hovvever, to avoid the animal eating substances which can have an abrasive effect on the bowel lining as they pass through, such as whole wheat grains and such trash materials as aluminium foil and string. Particularly to be avoided are bone spicules and it would appear preferable for affected animals not to be given bones in, any form.

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