Food Hypersensitivity in Pets

Food hypersensitivity is an uncommon skin disorder in dogs and
cats that is caused by an allergic reaction to food. The
component of the food that the animal reacts to is usually a
protein source (beef, chicken, egg, cow’s milk) but it may be a
minor component (preservative, additive, dye). Because this is
an acquired disease, the animal has often been fed the food for
months to years before the onset of the disease.

The most common sign of food allergy is an intense, nonseasonal
itch. In dogs, the itch tends to be generalized, but the ears,
face, and feet may be more severely affected. Some dogs may
exhibit signs of recurrent ear disease as the only manifestation
of food allergy. Food allergy in cats usually affects the face
and neck, and the itch may be so severe that the animal
scratches itself until it bleeds. Up to 15 per cent of animals
with food hypersensitivity have accompanying gastrointestinal
signs (vomiting and/or diarrhea). In both dogs and cats, the
disease may be poorly responsive to glucocorticoids (steroids).
The majority of dogs with food hypersensitivity manifest
clinical signs before 3 years of age, but the disease may occur
at any age.

The diagnosis of food allergy involves a food elimination trial.
There is currently no other accurate test to determine whether
your pet has food allergy. It is believed that animals may react
to allergens in their food for up to 6 weeks or more; therefore
a restrictive diet must be given for up to 10 weeks. Because
food allergy is an acquired disease (a food component becomes
allergenic after being fed), only foods that the animal has
never eaten before may be used. One protein source and one
carbohydrate source are chosen and all other foods are
discontinued. Cats may eat a single protein source for the
elimination trial. Your veterinarian will base the trial diet on
what your pet has eaten in the past. Therefore, it is important
to be complete when relating your animal’s diet history.

During a food elimination trial, only that diet is fed. Treats,
rawhide chews, dog biscuits, pig ears, chew hooves, vitamin
pills, food supplements, or unapproved medications (including
some heartworm preventives) should not be given. Your
veterinarian may change the heartworm preventive that your pet
is receiving to a nonflavored pill for the duration of the trial
period. You may not use cheese, hot dogs, and so forth to
disguise medication during the diet trial.

Treats must consist of the same ingredients used in the diet
trial. Outdoor cats must be kept away from other food sources to
have a successful food trial. It may be necessary to confine
them indoors for the duration of the food trial.

Please exercise caution if you have other pets and make certain
that the pet receiving the trial diet never has an opportunity
to eat any of the other animals’ food (or even lick their bowl).
One morsel of another type of food has the potential to
invalidate the entire elimination diet trial and could
necessitate commencement of a different diet for 10 weeks. The
other animals in the household could also be fed the elimination
diet. Inform everyone in the household that your pet is
receiving a special diet. It is important to be diligent when
your pet is on walks to ensure that ingestion of foodstuffs does
not occur. Simply changing the brand of dog food (even to diets
that are described as “hypoallergenic”) is not equivalent to an
elimination diet. Most dog foods share similar protein, grain
meal, preservatives, and/or dye sources and contain many
potentially allergenic ingredients in order to be fully
balanced. Your veterinarian will recommend a protein (e.g.,
fish, pork, tofu, lamb, pinto beans, rabbit, venison, duck) and
a carbohydrate (e.g., potato, rice, oatmeal) in a ratio of one
cooked pound of protein to six cups of cooked carbohydrate.
Flavorings other than salt, pepper, and garlic may not be used
(no oils, butters, or cooking spray). Many clients find it
easier to prepare the diet in bulk (e.g., 1 week at a time) and
freeze the diet in measured daily rations. Approximately one cup
is fed per 10 pounds of body weight daily. Switch gradually to
the new diet over a period of 3 to 5 days by giving more of the
new diet and less of the old diet each day.

Some animals may have loose stools while receiving the trial
diet. Your pet may develop vomiting, diarrhea, or constipation
or may refuse to eat the new diet. Cats may begin to develop a
serious liver disease if they do not eat for 2 days or more. Do
not allow your eat to go without eating for more than 2 days,
and consult your veterinarian if any of the other problems occur
before giving up or changing the diet. Cats may be especially
difficult to coax to eat the trial diet. If your veterinarian
approves, certain baby foods may be used for cats for the
elimination diet.

It is advisable to keep a daily diary during the trial so that
progress may be monitored. Many clients use a calendar to record
the level of itchy behavior (scale of 1 to 10) in conjunction
with the body areas the pet is targeting. In the event that your
pet refuses to eat the elimination diet, your veterinarian may
recommend a commercial prescription limited-antigen diet. It is
important that during the elimination diet no corticosteroids
(pills, drops, or creams) are administered to your pet, as these
drugs may cloud the assessment of the response to the trial
diet.

The elimination diet is not a balanced diet and it is not
recommended that pets continue to eat the diet for longer than
10 weeks without veterinary supervision. It is not necessary for
your pet to exhibit 100 per cent improvement while receiving the
diet; 50 per cent improvement may be sufficient to demonstrate
response to the diet trial. It is important to remember that up
to 30 per cent of food-hypersensitive dogs may exhibit multiple
allergies (flea allergy, environmental allergies); therefore,
the response to the diet may be partial. The confirmation of
food hypersensitivity is definitively determined by dietary
rechallenge. It is important to avoid changes in bathing, ear
treatments, oral medications.

The original diet should be slowly reintroduced over 3 to 5 days
and the pet monitored for increases in itching, which should
return within 14 days. If the itching returns, stop feeding the
original diet and revert back to feeding the elimination trial
diet until your pet returns to normal. If your pet is diagnosed
with food hypersensitivity, your veterinarian will work closely
with you to try to select a commercial diet that contains
ingredients to which your pet is not allergic. In rare
instances, pets may react to all commercial diets and must
receive a home-cooked diet. Your veterinarian may consult
veterinary nutritional specialists (usually located at
veterinary colleges) who can provide a recipe that completely
balances the home-cooked diet.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.