Around 5 - 10% of pets suffer from food intolerances, mirroring the trend amongst humans estimated at 40-45% of the population. Contrary to popular belief, food intolerance is likely to be associated with the food that is most commonly eaten.
Pets are most often allergic to wheat (e.g. biscuits) and beef; other common allergens include pork, chicken, milk, maize, soya and fish (Proceedings of the Nutrition Society. 64(4):458-464, November 2005. Day, Michael J.).
Recognising dietary intolerance is difficult for pet-owners as recurring signs are often passed off as minor illnesses such as eczema, dermatitis, vomiting, diarrhoea and lethargy, all of which can be difficult to attribute to diet alone as this can be caused by so many other disease processes. As a result, diagnosis and treatment can be a lengthy and thus costly exercise. Neurologic signs such as malaise and seizures rarely have been reported. Allergy tests carried out by vets can aid diagnosis, but can cost in excess of £200.
If you bring your pet to a veterinary surgery with a complaint of itching or digestive distress, your veterinarian will first rule out more common causes of these signs. The rule-out process might include a physical examination and laboratory tests for flea allergy dermatitis, the most common cause of allergic skin disease of animals, inhalant allergies, seasonal reactions to pollen, mold spores, and dust mites, and food caused digestive intolerance, an acute adverse reaction to food that does not involve the immune system.
If the food allergy remains a suspect, your veterinarian will then help you try to pinpoint what might be causing your pet's problems. Most food-allergic dogs are hypersensitive to only one or two ingredients, with beef and dairy proteins topping the culprit list. Ingredients that may also cause problems - but not as often - include grains, pork, chicken, eggs, and fish. Allergies to food additives including preservatives may also be a cause but are rare.
Once diagnosed, healing the problem is not so easy, made worse because of a lack of legislation governing pet food labelling, which means pet owners cannot always clearly identify what they are feeding their pets. Pet food manufacturers are currently not obligated to name actual ingredients and some pet food labels use general terms such as 'meat by-products' and 'cereal or animal derivatives'.
To definitely diagnose food allergies, most veterinarians recommend a trial with an elimination diet - a diet that contains a protein and carbohydrate source the animal has never been exposed to.
(source: More Than pet insurance survey, and Update on Food Allergy in the Dog and Cat from Stephen White, WSAVA conference)
Obtaining reliable information on the extent of food related intolerance (or as it tends to be called 'food allergy') is not easy, but there have been quite a few studies undertaken worldwide, and it is possible to piece together some accepted facts and recommendations from these studies.
I have included below a whole range of article extracts which you might like to look at, but rather than confuse you too much with technical jargon, I have put together a few points which you might like to consider if you feel that your dog or cat may have a food intolerance or allergy, which will manifest itself most probably as excess itching, bare and reddened skin or gastric problems.
Most importantly, of course, if your pet has a serious problem then you need to get a veterinary opinion on the possible causes, as not all skin and digestive disorders are food related (as we know from our own health and diet)
Stephen White, researching in the US has said 'No sex predilection has been reported for food allergy in dogs or cats. In some studies, no breed predilection was noted. In contrast, two studies found that certain dog breeds may have a risk for the development of food allergy:
Soft-Coated Wheaton Terrier, Dalmatian, West-Highland White Terrier, Collie, Chinese Shar Pei, Llasa Apsa, Cocker Spaniel, Springer Spaniel, Miniature Schnauzer, Labrador Retriever Dachshund and the Boxer. Breed data from Colorado State University shows that retrievers may be at greater risk to develop food allergy than other breeds of dogs. While the age at presentation has been reported as variable, several researchers now feel that at least 33% of their cases in dogs are of animals less than one year of age.'
A few points as to the possible course of action your veterinary surgeon may suggest:
Firstly, just changing from one commercial diet to another is probably not going to solve the problem, as it is difficult to know precisely what is is in a particular food, as labelling regulations are not tight enough.
An elimination diet is the only sure way to work out a) whether the problem is food related and b) what's causing the problem. An elimination diet is most often a bland diet of very well cooked rice with a single source of protein - Elimination diets for dogs include lamb, chicken, rabbit, horse meat and fish as sources of protein, with rice or potatoes. Successful elimination diets for cats include lamb, chicken, rabbit or venison, with rice. All other foods, treats, table scraps and tit-bits must be eliminated from the dog or cats diet. Elimination diets fail when the owner or someone else takes pity on their pet and introduces a treat before the end of the trial, the dog or cat managed to scavenge or find food from another source, the dog or cat is actually intolerant to one of the ingredients in the elimination diet or the dog or cat is suffering from factors other than food intolerance.
The diagnosis is conclusively proven by reproducing the symptoms by feeding the original diet after the elimination of signs on the new diet. The pet can then be fed on a commercial diet (or home-made food) without the offending allergen(s).
Unfortunately this is not a quick process, and the elimination diet should be continued until signs of the problem have gone. This process could take up to 10 weeks, as the study below shows:
If there are improvements the owner can then start to reintroduce other food items one at a time in order to determine what the animal is reacting to. Experts recommend that each new food must be introduced two weeks apart as some ingredients may cause a delayed reaction.
There is no cure for food allergies. Managing a food allergy means simply avoiding the causative ingredient or ingredients. Medications (such as antihistamines and corticosteroids) that reduce itching caused by other types of allergies usually don't work on food-induced itching.