Hypoallergenic Diets
My-Dog.info > Dogs, Diet & Food
In the last few years, commercially-formulated hypoallergenic
diets have become increasingly popular and readily available to
pet owners and veterinarians. This growth in the
"special-diet" segment of the petfood market reflects a
growing awareness of, if not necessarily an increased incidence
in, the occurrence of adverse reactions by dogs and cats to
commercial petfoods, including food allergy (hypersensitivity)
and dietary intolerance.
Food hypersensitivity is defined as an itchy skin disorder of
dogs and cats that occurs when a pet eats a diet that contains an
ingredient to which it is allergic. The major complaint and
primary consistent finding is itchiness.
Food allergies in dogs and cats are thought to account for
approximately 5% of all skin diseases and 15% of allergic skin
diseases seen in veterinary practices. The term "food
allergy" is often mistakenly used to describe adverse
reactions to food in general and should only be used to describe
food sensitivities that involve the immune system.
How and why animals get hypersensitive to foods remains poorly
understood. In most cases, the offending allergen is a protein
found in the diet called a "glycoprotein". It is not
know whether sensitization occurs in the lining of the intestines
or after the allergen is absorbed. In fact, it may be that
glycoproteins become allergenic only after digestion or as a
result of food processing (e.g. heating).
In dogs, the most common allergens are beef, dairy products,
chicken, wheat, eggs, corn and soy. In the cat, the most common
ones are fish, beef and dairy products. However, pets can be
allergic to foods other than these and to more than one kind of
food.
The most reliable and accurate method of diagnosing food
allergies is by means of an elimination diet which incorporates
"novel" protein and carbohydrate sources which the pet
is not normally exposed to. Blood tests are considered worthless.
The test diet must be free of additives (preservatives, food
colouring, flavouring). For this reason, when trying to determine
if a pet is allergic or not, commercial
"hypoallergenic" diets are unreliable as elimination
diets and should not be relied upon. Instead, the test diet must
be homemade. In dogs, commonly used ingredients include tuna fish
(canned in water), rabbit, venison, turkey, duck, and
lamb/mutton. In cats, frequently used ingredients include rabbit,
venison, or strained lamb or ham baby food. These can be mixed
with potatoes, rice, or tapioca in both canine and feline diets.
Since these diets are not adequately balanced nutritionally,
vitamin, mineral and essential fatty acid supplementation is
necessary if a prolonged testing period is anticipated. For most
dogs and cats, a test diet consisting of 1/3 protein, 2/3
carbohydrate, 2% corn oil (on dry matter basis), supplemented
with a vitamin and mineral mixture, will meet the animal's
nutritional and essential fatty acid requirements for the short
term.
In the past, veterinarians used a feeding trial of only 3
weeks duration to rule out food allergy but this has proven to be
inadequate. A home-made elimination diet must be fed for up to 10
weeks in both dogs and cats, and in some cases, as long as 13
weeks, in order to truly rule out allergies. During this time
period, nothing else must be fed to the pet, including snacks,
treats, rawhide chew toys, etc.
If itchiness is reduced significantly or ceases completely
while on the trial diet, the offending diet should be fed again.
Itchiness should recur within 48 hours, although it may recur as
late as 10-14 days post-feeding. A return of itchiness after
feeding the "old" diet again confirms the diagnosis of
food hypersensitivity. A search for the offending ingredient(s)
can then be instituted.
Once the diagnosis of food allergy has been made, a
commercially available "'hypoallergenic" diet can be
chosen.
Reprinted with permission from www.animalhealthcare.ca
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