The condition affects the large intestine (or colon) which is the last part of the gastrointestinal tract. It is seen in both dogs and cats, but is more common in dogs.
The problem is caused by an excessive immune response to food material in the large intestine. This probably occurs because tiny molecules of food penetrate into the wall of the large intestine. Once in the wall they will be recognised as foreign invaders just like bacteria or viruses and the immune system sends in an army of white blood cells to fight them. This clogs up the wall of the large intestine with white blood cells, thickening it and preventing it from doing its normal task of absorbing water from the faeces. Some dogs may experience this reaction to normal dog food, but others may only experience an episode of colitis after they have scavenged on a walk or been fed something too rich at home.
The clinical effects of colitis relate to diarrhoea originating in the large intestine which is markedly different from that originating in the small intestine. The large intestine tends to empty quickly and, after the initial few passages of diarrhoea, the volume of faeces reduces and the patient is often left straining unproductively. The urge to go to the toilet is high and animals may be distressed that they want to go, but there is nothing left to pass. Mucus (looking like jelly) and fresh blood (often copious) is common and reflects damage to the lining of the large intestine. Often once the straining is unproductive, the patient is left passing nothing but small amounts of mucus and blood. The condition is often painful and the animal will be distressed. About 30% of animals may also vomit.
There is a tendency of owners and carers to panic when they first see a pet with colitis due to the presence of blood in the diarrhoea, but in most cases this makes the condition appear more severe than it is.
Provided the pet is bright and well in themselves, the first line of treatment is to withdraw food for 24 hours and offer water little and often to maintain hydration. A bland diet can then be introduced and, over the next few days, the pet can be moved gradually back to normal food.
However, if this does not resolve the problem, or if the patients is depressed and subdued from the outset, veterinary care needs to be sought and vets will use a combination of injections to reduce inflammation in the bowel and if necessary prevent further vomiting.
As always, prevention is better than cure so make sure you question your customers as to what their dog eats normally and whether it has shown any previous signs of bowel disease. Stick to the dog’s normal food and do not be tempted to offer treats which the dog is not used to.
