Issue Description Food allergy is an allergic reaction to one or
more ingredients in a pet's food. The most common allergens are beef
and milk products, cereals (wheat, corn, soya), chicken and eggs.
Causes The most common food allergens are beef,
chicken, pork, fish, milk, whey, eggs, corn and soy. All these foods
are high in protein. The reason that proteins are so often involved is
that they are very large molecules, each component of which can
combine with an antibody or immune system T-cell receptor to produce
an allergic reaction.
Food allergies will show up within 4
to 24 hours of eating the allergenic food, at least in the early
stages. Later on, the dog will show symptoms constantly. As in other
types of allergies, skin problems are the common signs, but some dogs
also vomit, and have diarrhea or gas.
Allergies can cause more than itching. In response to the allergen,
the sebaceous glands of the skin may become over-productive, altering
the normal condition of the skin. This leaves the skin open to
infection (pyoderma). Pyoderma causes not only MORE itching, but also
pain and inflammation, ear infections, or even abscesses beneath the
Symptoms Symptoms of a food allergy are itching, licking
or chewing. Otitis Externa (ear infection) along with other skin
problems are also common in conjunction with food hypersensitivity.
Some pets may also have diarrhea and other digestive problems.
Symptoms can appear at any age, whether a pet has just started a new
diet or has been eating the same food for several years.
Diagnosis Diagnosis and management of food allergy in the
dog has been made easier in recent years because of new unique
protein/limited ingredient diets available in veterinary medicine. The
length of the diet trial has been extended from three weeks up to
10-12 weeks. Studies have shown that some dogs may not show
significant improvement on their diet trial until 10 - 12 weeks into
the food trial. It is doubtful that a dog that is experiencing no
change in clinical signs at eight - nine weeks will improve
dramatically after that time.
Diets containing fish, lamb,
duck, venison, rabbit, kangaroo, modified soy, modified chicken livers
etc.. as the protein source are all commercially available. Most of
these diets are as limited as possible in the remainder of their
ingredients. The concept of protein modification to reduce
antigenicity has been utilized in formulation of Hill's z/d ultra, low
allergen and Iam's H/A. In addition, many diets contain an increased
amount of omega three fatty acids or decreased omega 6 to omega 3
fatty acid ratios to decrease the formation of inflammatory mediators
in the skin.
The most important concept to remember is an
immunologic response can be mounted to any substance (especially
protein) that has not been modified to the point of rendering it
potentially non-allergenic. Thus, it is very important to obtain a
complete dietary history from the client concerning their pet before
choosing a food for the food allergy elimination diet trial if
choosing a novel protein source diet. None of the substances in the
food trial diet should have been in the previous diet(s) of the
patient. In addition, the patient should be placed on non-chewable,
non-flavored heartworm prevention for the length of the diet trial.
The patient should be allowed no other treats, chew toys, raw hides
etc. Cheating on the diet by giving treats, animal eating garbage, or
scavenging under the high chair can occur.
If the animal is
severely pruritic, a short course of oral short acting corticosteroids
or other non-steroidal anti-inflammatory medication may be warranted.
This therapy must conclude a few weeks before the end of the dietary
trial. At the end of the trial, an apparent response to the test diet
(no symptoms) should be confirmed with a challenge, using the former
diet. Symptoms should reappear on average in a few hours up to 5-7
days. Any secondary skin diseases (seborrhea, Malassezia or
staphylococcal folliculitis) should be cleared before the trial or the
coexistent problems need to be treated throughout the length of the
diet trial and into the re-challenge phase. If the only complaint is
recurrent staphylococcal folliculitis or Malassezia dermatitis, a
relapse rate must be established prior to institution of the diet
trial and the diet must be given for longer than the relapse interval.
After a positive diagnosis has been confirmed by re-challenge, the
animal should be placed back on the test diet until asymptomatic again
OR if the owners wish to find the problematic ingredient, then
suspected ingredients can be added one at a time. Alternatively, the
animal can be continued on the test diet. In these instances, only a
tentative diagnosis of food allergy can be made.
Treatment The only therapy is to avoid the allergen. Many
owners will elect to continue on the "food trial" commercial diet. If
they do not wish to pinpoint the individual allergen, they should be
encouraged to keep a list of the food substances that has been
previously fed to their pet. With this information, if they desire to
change diets or if the diet being fed becomes unavailable, they may be
able to choose another commercially available diet that avoids
proteins from the "potentially offending protein" list.