At the Animal Clinic at Thorndale, one of the most common conditions we see affecting dogs is allergy. In the allergic state, the dog’s immune system “overreacts” to foreign substances (allergens or antigens) to which it is exposed. These overreactions are manifested in three ways. The most common is itching of the skin, either localized (one area) or generalized (all over the dog). Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge. The third manifestation involves the digestive system, resulting in vomiting or diarrhea.
Types of Allergy
There are five known types of allergies in the dog. Each of these has some common expressions in dogs, and each of these also has some unique features.
- contact
- flea
- food
- bacterial
- atopy (previously called “inhalant”)
Food Allergy
A food allergy is a condition in which the body’s immune system reacts adversely to a food or an ingredient in a food. Most commonly the dog iexhibits itching, and some may have digestive problems. The allergic reactive cells in the dog are primarily located in the skin.
Any food or food ingredient can cause an allergy. However, protein, usually from the meat source of the food, is the most likely offender. Proteins commonly found in dog foods are derived from beef, chicken, lamb, and horsemeat. To test for a food allergy, the dog needs to be fed a novel diet, consisting of none of the ingredients it has so far eaten in its lifetime. Other additives may also be allergens. Novel diets, such as whitefish and peas are available, but a better choice is a hydrolyzed protein diet such as prescription diet Z/D. Keep in mind that even though your dog may have a food allergy, it may also have allergies to pollen, dust, fleas, contact substances or surfaces, and/or bacterial allergies as well.
It is important to remember that allergies cannot be cured, only controlled.
Lamb and Rice Diets
Although many people think lamb and rice diets are hypoallergenic, they are not. They are not inherently less likely to cause allergy than other diets. However, they have this reputation because several years ago there were no dog foods on the commercial market that contained lamb. A manufacturer of prescription dog foods formulated a food from lamb that was suitable for allergy testing, which will be explained below. Because of that situation, lamb-based dog food was considered “hypoallergenic.” Now there are many lamb based diets commercially available. Some dogs are allergic to lamb.
Food Allergy Testing
Dogs are not likely to be born with food allergies. More commonly, they develop allergies to food products they have eaten for a long time. The allergy most frequently develops in response to the protein component of the food; for example, beef, pork, chicken, or turkey. A food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress. We recommend testing for food allergies when the clinical signs have been present for several months, when the dog has a poor response to steroids or antihistamines, or when a very young dog itches without other apparent causes of allergy. Testing is done with a special hypoallergenic diet. Because it takes at least 4 weeks for all other food products to get out of the system, the dog must eat the special diet exclusively for 6-10 weeks (or more). If a positive response occurs (the itching stops), you will be instructed on how to proceed. If the diet is not fed exclusively, it will not be a meaningful test. We cannot overemphasize this. If any type of table food, treats or vitamins are given, they must be discontinued during the testing period. There may be problems with certain types of chewable heartworm preventative, as well. Your veterinarian will discuss this with you.
Because dogs that are being tested for inhalant allergy often also itch year round, a food allergy dietary test can be performed while the inhalant test and antigen preparation are occurring. Many dogs will have concurrent inhalant and food allergies, just like their human counterparts.
INSTRUCTIONS:
Type of food for a food allergy food trial. Z/D diet is a hypoallergenic diet that can be fed exclusively during a food trial. The proteins in Z/D are hydrolyzed into smaller peptides and amino acids and generally do not act as allergens. If your dog stops itching while on Z/D, a food allergy is confirmed. At that point you may gradually (1 per week) begin to add back in, one at a time, other proteins the dog has eaten. As long as the dog remains itch free, the added protein is not the offending allergen.
During the food trial, your dog is to exclusively eat a hypoallergenic diet. If it will not do so readily, mix it 25:75 with the current diet for several days, then gradually increase the special diet to 100%. If this does not work, contact us for an alternative plan. Discontinue any chewable treats or vitamins, including heartworm preventatives. Table food is not allowed. Offer only distilled water to drink, if that is possible.
If your dog also has a flea allergy or has enough fleas to make the other allergy problem worse, flea control is very important and should include treating the dog and its environment. Bear in mind that flea allergies often accompany other types of allergies, especially inhalant allergy.
If your dog also has a bacterial skin infection secondary to a food allergy, antibiotics and topical medications and shampoos may be dispensed.
If your dog also has inhalant allergy, medications will be dispensed to control itching from atopy.