A change in diet is not necessary for development of food allergy. About 70 percent of affected pets develop allergies! to food ingredients that they have been fed for a long time, usually more than two years. In fact, if your dog has an immediate adverse reaction to a new food, it is probably not an allergic reaction, because it takes more than one exposure to produce an allergic reaction.
Food ingredients most commonly responsible for allergies are beef, chicken, fish, eggs and milk. The tendency to develop allergies is genetically determined. Dogs with other allergies like inhalant allergies or atopy may be at increased risk for developing a food allergy
...New food allergies can develop over time. If your dog was diagnosed previously with food allergy and has been well controlled with a special diet but once again is showing signs of allergic skin disease, he may have developed a new allergy. Under these circumstances, consult your veterinarian to determine whether a new allergy has developed or whether another disease is present.
... genetic predisposition seems to exist for food allergy. Based on their genetic constitution, some animals seem to be predisposed to development of food allergy. However, since the cause of food allergy is unknown, the disorder cannot be prevented.
...The foods most commonly incriminated as allergens in dogs are beef, dairy products and wheat and account for 66 percent of suspected cases of food allergy. Chicken, lamb, soy, eggs, pork, and preservatives account for only 22 percent of reported cases according to a recent survey of veterinarians in North America.