Cats tend to develop food allergies to a familiar food and these can be part of multiple allergies. Food intolerances tend to be to new foods and are usually present from birth, but can occur later in the cat’s development. As far as an owner is concerned, the symptoms, diagnosis and treatment are similar.
Common symptoms of food allergy or intolerance include chronic vomiting, colitis, irritable bowel syndrome, diarrhoea, failure to gain weight or weight loss, poor or dull coat, lack of energy. Less commonly food allergies may express themselves in a cat’s skin. The hallmark of a skin allergy is itchiness. Fur balls or hairs around the tongue, teeth or house may be signs of excessive licking. Some cats will appear to go bald, although the hairs are really being broken off by licking. Crusting and ulcers around the head and neck may suggest food allergies. Some cats develop large red, moist and weeping sores.
Your vet will want to rule out other possibilities like dietary upsets, internal parasites, infections, metabolic diseases of the kidney, liver and pancreas, and, in older cats, various cancers.
If the cat has skin symptoms, the vet must rule out parasites such as fleas, lice and mites.
Your vet will recommend a trial diet using foods new to your cat. Home cooked diets using a single protein (e.g. meat or fish) and carbohydrate (e.g. rice or potatoes) with water to drink are best. Give the same amount as tinned or half-again as much as dry foods. Hypoallergenic diets are available from your vet if necessary. Other cat-foods contain a variety of ingredients that vary from batch to batch and are not suitable. Trial diets should be fed for six weeks. Cats should not be fed anything else during the trial. Cats that hunt or are fed elsewhere may need to be kept indoors.
Allergic diseases will wax and wane, so an improvement does not necessarily mean the cat has food allergy. A relapse within 1-2 weeks on the original diet confirms a food allergy. Once the cat is stable again on the trial diet, introduce ingredients such as beef, lamb, dairy products etc. one at a time to discover which the cat reacts to. These can then be avoided. Alternatively, a commercial hypoallergenic diet can be tried.
If the food trials identify the food ingredients which are making your cat ill, then your vet will help you choose a diet which excludes these ingredients. You will need to keep your cat on this diet for the rest of its life.
If the symptoms do not clear up after food trials, it is usually a good idea to ask your vet to refer you to a veterinary specialist. There are inflammatory and other bowel conditions which can trigger a food allergy. These can be diagnosed by endoscopic investigations and biopsies. A vet who specialises in gastroenterology or internal medicine will have the equipment and expertise to do these investigations.
If the symptoms are mainly on the skin, then a veterinary skin specialist can help. It may be that there are factors, other than just food allergy, which are triggering the skin disorder.