Dogs sometimes have an intolerance or an allergic reaction to one or more food ingredients—usually part of the protein content—and this manifests itself as itching or diarrhea. As the person looking after your pet and managing his diet, you have to work with your vet to discover which ingredient(s) is causing the problem, and then eliminate it from your dog's diet. Food allergies are caused by an abnormal immune response to one or more diet ingredients, while a food intolerance is an abnormal reaction that does not involve the immune system. Fortunately, food allergies rarely have severe consequences in dogs.
What is food allergy?
Veterinarians estimate that food allergies cause 1% of all skin problems and about 10% of all skin allergic issues in dogs. Other allergic skin problems, such as allergy to flea bites, are more common. Nobody knows exactly what percentage of gastrointestinal problems, such as vomiting or diarrhea, are caused by food allergies. This is because pet owners often change the food they feed their dog until they find one that is tolerated. In general, dogs that are truly allergic will have skin issues, while those who are intolerant will have diarrhea and/or vomit.
The exact way a food ingredient in the diet causes the symptoms of food allergy is unknown. Sensitivity reactions, such as itching of the skin, vomiting, or diarrhea, may occur within minutes to hours, or even several days later.
The offending dietary ingredient is not necessarily something new in the diet. Your dog can develop allergies to foods he's been eating for years, and the allergy may come on suddenly. Once an allergy has developed, the sensitivity to the ingredient will likely last a lifetime. So foods containing that ingredient need to be kept out of your dog's diet permanently.
Which ingredients cause food allergy?
Any food ingredient you've been feeding your dog can cause hypersensitivity reactions. Anything that contains protein can be a culprit, such as beef, eggs, wheat gluten, and lamb. Though some animals develop diarrhea when they consume milk, this is not regarded as a true allergy; it's described as an intolerance.
Diagnosing food allergy
Food allergies are not seasonal, though other skin allergies usually are. However, skin irritation and scratching can result from causes other than food allergy. And many dogs with food allergies also have skin allergies to other substances. That's why it's important for you to carefully consider other causes, such as an allergy to fleas. If your dog's skin damage is severe and is making him irritable and miserable, your vet may prescribe anti-inflammatory drugs until the "itch-scratch" cycle ends.
The elimination diet
To get to the bottom of the problem, your vet may ask you to list all the foods in your dog's diet, including treats, bones, and table scraps. Your vet will look through this list for foods that commonly trigger an allergic reaction in dogs. The next step is to eliminate one item at a time from your dog's diet to see if his allergic reaction goes away. This elimination diet may continue until the offending food is discovered.
Feeding your dog only the elimination diet for the prescribed time is the best diagnostic procedure to find out if your dog has a food allergy. It may take up to 6 or even 10 weeks for the itching caused by the allergy to completely disappear, so it's important for the elimination diet to be nutritionally complete to prevent nutritional deficiencies and ill health. Your dog may be showing gastrointestinal signs such as diarrhea, but these usually go away within a few days.
Alternatively, your vet may prescribe a limited antigen diet. This is a diet that contains very few ingredients that may cause an allergic response. These diets may also contain ingredients that aren't common in dog foods. A hypoallergenic diet may also be prescribed. This diet contains proteins that are too small to likely cause a reaction. Once the itching has stopped and the skin irritation has resolved, a food challenge may be initiated.
The food challenge
To find out which protein sources your dog is allergic to, your vet may recommend testing different protein sources once your dog's clinical signs have improved. The way you do this test is to introduce suspected food items to the diet in small quantities, one new food ingredient every 6 to 8 weeks. If the itching or diarrhea your dog previously experienced comes back, you've likely succeeded in your sleuth work and discovered an offending food ingredient. Remember, many dogs are allergic to more than one ingredient, so be sure to use the food challenge for any ingredient or treat you want to offer your dog. If, however, you don't want to try the food challenge, and your dog is happy on the elimination diet, you may continue to feed him those safe foods, as long as they represent a complete and balanced diet.
Guidelines for care and attention
Here are a few guidelines to help you identify the source of your dog's food allergy:
- If your dog has been prescribed drugs, make sure you administer them exactly as prescribed. Ask for medications that are not flavored or chewable, as the flavorings can cause allergy issues with some dogs.
- Make sure your dog has access to a plentiful supply of clean, fresh water. Eliminate other fluids, such as milk and chicken broth while your pet is on the elimination diet. These can be reintroduced as a food challenge.
- When feeding your dog the elimination diet, give him absolutely no other foods or treats or table food.
- You may need to feed your dog the elimination diet for up to 10 weeks before all the allergic signs disappear. Be patient!
- Watch your dog closely for remission or a decrease in severity of signs during the elimination diet period, and let your vet know about any improvements or reactions to specific foods.