Pet
Food
Review

Pet food intolerance and allergy

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)

The elimination diet

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:

1. 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.

2. 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.

3. 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).

4. 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:

5. 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.

6. 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.

Foods for sensitive dogs and cats

There are a range of foods labelled as hypo-allergenic - that is they contain ingredients which are generally considered to be highly digestible and therefore less likely to upset a sensitive digestion.

For the best information on a wide range of specialist foods we recommend checking online with the two big online pet supermarkets, Pets at Home and Pet Supermarket

Extracts from technical papers relating to food intolerance and allergy

Below are extracts from a range of technical papers relating to the subject of food intolerance, which it might be possible for you to follow up (although access to the papers is often a case of paying for the privilege).

Food allergy in dog and cat
Vroom MW.
Food allergy in the dog or cat can only be described as non-seasonal dermatitis accompanied by scratching. When the term 'food allergy' is used, an immune-mediated reaction is not always meant, although the term would suggest that it is. The frequency of occurrence of food allergy is unknown, with the literature giving widely differing percentages. Type I and type IV hypersensitivity reactions probably play a role in the pathogenesis, although a type III reaction is also thought to be involved. Gastrointestinal disturbances and skin complaints are symptoms of food allergy, and scratching is nearly always mentioned as the most common sign. The diagnosis can only be made by feeding the animal on a hypoallergic diet, which must be given for several weeks. Diagnostic tests are unreliable. The patient should not have been previously exposed to the ingredients of the hypoallergic diet. As 'home-made' diets may be deficient in minerals, vitamins, and essential amino acids, these ingredients must be supplemented if the diet is to be maintained for a long time. The prognosis of food allergy is good if the causative ingredient is identified. It is important the animals' owner is given through instruction. Medicines have little effect on food allergy.
PMID: 7974444 [PubMed - indexed for MEDLINE]

Verlinden A, Hesta M, Millet S, Janssens GP.
Laboratory of Animal Nutrition, Department of Animal Nutrition, Genetics, Breeding and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, B-9820, Merelbeke, Belgium. AM.Verlinden@ugent.be
Food allergy (FA) is defined as "all immune-mediated reactions following food intake," in contrast with food intolerance (FI), which is non-immune-mediated. Impairment of the mucosal barrier and loss of oral tolerance are risk factors for the development of FA. Type I, III, and IV hypersensitivity reactions are the most likely immunologic mechanisms. Food allergens are (glyco-)proteins with a molecular weight from 10-70 kDa and are resistant to treatment with heat, acid, and proteases. The exact prevalence of FA in dogs and cats remains unknown. There is no breed, sex or age predilection, although some breeds are commonly affected. Before the onset of clinical signs, the animals have been fed the offending food components for at least two years, although some animals are less than a year old. FA is a non-seasonal disease with skin and/or gastrointestinal disorders. Pruritus is the main complaint and is mostly corticoid-resistant. In 20-30% of the cases, dogs and cats have concurrent allergic diseases (atopy/flea-allergic dermatitis). A reliable diagnosis can only be made with dietary elimination-challenge trials. Provocation testing is necessary for the identification of the causative food component(s). Therapy of FA consists of avoiding the offending food component(s).

Diagnosis and management of food allergy and intolerance in dogs and cats.
Wills J, Harvey R.
Waltham Centre for Pet Nutrition, Waltham-on-the-Wolds, Leics, UK.
This paper reviews food allergy and intolerance in dogs and cats. Adverse reactions to ingested food components can affect many systems and can produce signs involving the skin, gastrointestinal tract, respiratory tract and central nervous system, and these clinical signs are reviewed. Most basic food ingredients have the potential to induce an allergic response, although most reactions are caused by proteins. In particular, dogs and cats can become sensitive to cow's milk, beef, fish or cereal. Food allergy and intolerance is rare in dogs and cats, although the incidence in practice is difficult to establish. Clinical signs are quite variable, depending on the individual response, although the major clinical sign is pruritus. Diagnosis can be difficult, as there is no single test available to help the clinician to confirm or refute the presence of food sensitivity. Diagnosis is based on dietary investigation in the form of elimination diets and test meals. 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. Improvement in clinical signs while on the elimination diet is suggestive of food allergy. The diagnosis should be confirmed by feeding the original diet, with the development of clinical signs within 7 to 14 days of feeding.
PMID: 7848179 [PubMed - indexed for MEDLINE

Feed allergy in dogs and cats--not only a gastrointestinal problem
Ballauf B.
I. Medizinischen Tierklinik, Ludwig Maximilians Universität München.
Immunologically mediated reactions to foods are responsible for up to 10% of all allergic syndromes in dogs and cats. Skin lesions (pruritus, erythema and papules) represent the main manifestation (70 to 80%) compared to only 10 to 15% incidence of gastrointestinal signs in combination with skin problems or alone. Diarrhea, vomiting, low appetite, chronic weight loss, abdominal pain and lethargy are the most common signs involved in gastrointestinal food allergy. There exists no breed or sex predilection in dogs or cats; signs may occur at any time during life time. The immunological nature of the disease can only be guessed at from anamnestic and clinical features and must be verified by presence of lymphocytes, plasma cells, mast cells and eosinophilic granulocytes in histological specimens. At this time, the responsible allergen can only be identified in a restriction diet trial based on food which the animal has not been fed before, given exclusively for at least four weeks to the pet. Changing from one brand of commercial diet to another is not recommended. 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).
PMID: 8470106 [PubMed - indexed for MEDLINE]

Food hypersensitivity in 30 dogs.
White SD.
Food hypersensitivity was diagnosed in 30 dogs. Clinical signs varied, with pruritus (97%), erythema (50%), and papules (37%) being the most common. Diagnosis was based on resolution of clinical signs when the dogs were fed a restricted ("hypoallergenic") diet, and recurrence of signs when fed their original diet or other foods. No age, breed, or sex predilection was noticed. None of the owners could relate the onset of clinical signs with a recent change in diet. Seven dogs had concurrent fleabite, inhalant, intestinal parasite, or insulin hypersensitivity.
PMID: 3700223 [PubMed - indexed for MEDLINE

Food hypersensitivity in cats: 14 cases (1982-1987)
White SD, Sequoia D.
Department of Medicine, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.
Food hypersensitivity was diagnosed in 14 cats. Clinical signs varied; pruritus (100%), alopecia (64%), and papules (21%) were the ones most commonly observed. Pruritus was localized principally to the head or to the neck or ear region in 42% of the cats. Diagnosis was made on the basis of resolution of clinical signs when cats were fed a restricted ("hypoallergenic") diet, and recurrence of signs when cats were fed their original diet or other food. The most common allergens (on the basis of dietary challenge exposure) were fish and dairy products. Age or sex predilection was not observed, and 9 (64%) of the cats were domestic shorthairs. Owners could not relate the onset of clinical signs with a recent change in diet. Three cats had concurrent flea bite, inhalant, or flea collar hypersensitivity.
PMID: 2925487 [PubMed - indexed for MEDLINE

Food sensitivity in cats with chronic idiopathic gastrointestinal problems.
Guilford WG, Jones BR, Markwell PJ, Arthur DG, Collett MG, Harte JG.
Institute of Veterinary, Animal, and Biomedical Sciences, Massey University, Palmerston North, New Zealand. W.G.Guilford@massey.ac.nz
The objectives of this study were to investigate the prevalence of food sensitivity in cats with chronic idiopathic gastrointestinal problems, to identify the food ingredients responsible, and to characterize the clinical features. Seventy cats that presented for chronic gastrointestinal signs underwent diagnostic investigation. Fifty-five cats had idiopathic problems and were entered into the study. Diagnosis of food sensitivity was made by dietary elimination-challenge studies by using commercial selected-protein diets as the elimination diet. Sixteen (29%) of the 55 cats with chronic idiopathic gastrointestinal problems were diagnosed as food sensitive. The clinical signs of another 11 cats (20%) resolved on the elimination diet but did not recur after challenge with their previous diet. The foods or food ingredients responsible for the clinical signs were dietary staples. Fifty percent of affected cats were sensitive to more than 1 food ingredient. The clinical feature most suggestive of food sensitivity was concurrent occurrence of gastrointestinal and dermatological signs. Weight loss occurred in 11 of the affected cats, and large-bowel diarrhea was more common than small-bowel diarrhea. Assay of serum antigen-specific immunoglobulin E (IgE) had limited value as a screening test, and gastroscopic food sensitivity testing was not helpful. In conclusion, adverse reactions to dietary staples were common in this population of cats, and they responded well to selected-protein diets. Diagnosis requires dietary elimination-challenge trials and cannot be made on the basis of clinical signs, routine clinicopathological data, serum antigen-specific IgE assay, gastroscopic food sensitivity testing, or gastrointestinal biopsy.
PMID: 11215916 [PubMed - indexed for MEDLINE]

Diagnosis of food allergy in dogs.
Rosser EJ Jr.
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Veterinary Medical Center, Michigan State University, East Lansing 48824-1314.
The diagnosis of food allergy was confirmed in 51 dogs while the responsiveness to a 60-day home-cooked restricted dietary trial (elimination-diet trial) was evaluated. The primary clinical sign of allergy detected and evaluated in all dogs was persistent and nonseasonally pruritic skin disease. The duration of time between starting the elimination-diet trial and remission of clinical signs was recorded. Dogs were then reexposed to diets that had been fed before testing, and the duration of time before pruritus recurred was recorded. The elapsed time during which dogs were being fed an elimination diet before remission of clinical signs was 1 to 3 weeks in 13 dogs, 4 to 6 weeks in 25 dogs, 7 to 8 weeks in 10 dogs, and 9 to 10 weeks in 3 dogs. Findings indicated that the recommendation of a 3-week elimination-diet trial for diagnosis of food allergy was adequate for only 25% of the dogs. It is recommended that test diets be fed for at least 10 weeks before a food allergy is ruled out.
PMID: 8407485 [PubMed - indexed for MEDLINE

Responses of dogs with food allergies to single-ingredient dietary provocation.
Jeffers JG, Meyer EK, Sosis EJ.
Animal Allergy and Dermatology Clinic, Gaithersburg, MD 20877, USA.
OBJECTIVE--To characterize specific food ingredients causing allergic reactions in dogs and to assess cross-reactivity between proteins derived from a single animal source or from different plant products. DESIGN--Prospective study. ANIMALS--25 dogs with histories and cutaneous signs consistent with food-allergic dermatitis. PROCEDURE--Dogs were fed a food-elimination diet until resolution of clinical signs and then challenged with their original diet. A diagnosis of food allergy was made if there was complete return of pruritus within 14 days of challenge exposure. After diagnosis, dogs were fed the food-elimination diet until signs related to dietary challenge abated. The dogs then were fed beef, chicken, chicken eggs, cows' milk, wheat, soy, and corn in single-ingredient provocation trials for 1 week. Any cutaneous reactions to these food ingredients were recorded by their owners. RESULTS--Beef and soy most often caused adverse cutaneous reactions, although all ingredients induced clinical signs in at least 1 dog. Mean number of allergens per dog was 2.4, with 80% reacting to 1 or 2 proteins and 64% reacting to 2 or more of the proteins tested. A significant difference was found between dogs reacting to beef versus cows' milk and between dogs reacting to soy versus wheat; thus, the hypothesis of cross-reactivity to ingredients derived from a single animal source or to different plant products was not supported. Similar differences between chicken meat and eggs were not identified. CLINICAL IMPLICATIONS--Long-term management of dogs with food allergies is facilitated by identification of the most commonly encountered food allergens. Because cross-reactivity cannot be verified, each protein source should be included separately in food-provocation trials.
PMID: 8755979 [PubMed - indexed for MEDLINE

Food sensitivity in the dog: a quantitative study.
Chesney CJ.
Over a period of one year, 251 dogs were presented to a UK-based dermatology referral clinic. Eighty-five of these were either diagnosed as having symptoms compatible with atopy (58 dogs), or suffered from chronic otitis or recurrent pyoderma. All 85 were placed on a carefully restricted diet for eight to nine weeks in an attempt to establish whether the symptoms were due to food sensitivity. In total, 19 were shown to have food sensitivity, representing 7.6 per cent of all dogs presented to the clinic, and one-third (32.7 per cent) of those dogs with signs compatible with a diagnosis of atopy. In five dogs with proven food sensitivity, otitis was the principal clinical sign and, in two others, recurrent pyoderma. In the population studied, labradors appeared to be predisposed to the condition. Improvement was monitored by asking owners to assess their dog's symptoms on an ordinal scale of pruritus. In those cases in which food sensitivity was confirmed, significant reduction in pruritus occurred. Most of these could be maintained long term on a commercial restricted-component diet. Particular effort was made to ensure owner compliance with the diet trials, using an explanation and model based upon a Venn diagram showing assumed links between atopy and several 'flare factors'. It was found that this approach significantly enhanced client understanding and cooperation. It is concluded that a careful approach, monitored by active clinical audit, will help to establish the true incidence of food sensitivity.
PMID: 12038852 [PubMed - indexed for MEDLIN

Other possible references

References

1. Carlotti DN, Remy I, Prost C: Food allergy in dogs and cats: A review and report of 43 cases. Vet Dermatol 1:55-62, 1990.

2. Denis S, Paradis M.: L’allergie alimentaire chez le chien et le chat. 2. Étude rétrospective. Med Vét Québec 24:15-20, 1994.

3. Harvey RC: Food allergy and dietary intolerance in dogs: a report of 25 cases. J Sm Anim Pract 34:175-179, 1993.

4. Paterson S: Food hypersensitivity in 20 dogs with skin and gastrointestinal signs. J Sm Anim Pract 36:529-534, 1995.

5. Rosser EJ: Diagnosis of food allergy in dogs. J Am Vet Med Assoc 203:259-262, 1993.

6. Rosser EJ: Food allergy in the cat: a prospective study of 13 cats. In Advances in Veterinary Dermatology Vol 2, Ihrke PJ, Mason I, White SD (eds), 33-39, 1993

7. White SD. Food allergy in dogs. Compendium of Continuing Education for the Private Practioner, 20:261-269, 1998.

8. White SD, Sequoia D: Food hypersensitivity in cats: 14 cases (1982-1987). J Am Vet Med Assoc 194:692-695, 1989.