FOOD ALLERGIES
A food allergy is an over reaction by the body's immune system to one, or more than one, substance that a dog or cat eats or has eaten. The allergic reaction may show up as vomiting, diarrhea or weight loss. Or it may manifest itself with skin symptoms - itching, redness or hives involving the face, ears, feet and legs, abdomen, back, rectal area or any combination of these. Occasionally, food allergies can cause seizures, urinary tract inflammation or other problems. About 50% of the time in cats and 18% of the time in dogs symptoms are present in more than one body system - for example itchy skin and diarrhea both.
Food allergies are genetic and probably inherited. Certain breeds, such as Labrador retrievers and German shepherds, are more prone than others, but food allergies can occur in any breed. The dog or cat with food allergies was born with a gene that turns on at some point in his or her life. That gene may activate at three months or 13 years of age, or anytime in between. The majority of pets are between 1 and 3 years old when symptoms begin. When that gene turns on and starts triggering the immune system, the dog or cat will become sensitized to one or more food items it eats during the next few months. For reasons we don't yet understand, after a few months the gene seems to turn itself off again. After the initial 6 months of sensitization, animals will rarely develop additional sensitivities. In other words, whatever they become allergic to in the first 2-6 months after their inherited gene turns itself on they will be allergic to for the rest of their life, but they probably won't become allergic to additional food items after that. (This in NOT the case with allergies to pollens, dust mites, mildew or other inhaled substances. It is common to gradually become allergic to more and more inhalant allergens with time.)
There are no hypoallergenic foods. There is no food your pet can put in its mouth that it cannot become allergic to. Feeding a lamb-based food does not prevent food allergy. Your pet will simply develop an allergy to lamb, instead of to beef or chicken or whatever else it would have eaten instead. Your pet can be allergic to one or to many food items, and it can be allergic to ANYTHING it may have swallowed during the 6 months or so it was developing allergies. Rawhide chews, cow hooves, doggie toothpaste, the corn chips that fell on the floor, the fish residue in the cat poop he ate from the litter pan, the pork in the neighbor's garbage, the milk licked from the cereal bowl, the mouse caught in the basement and of course his cat or dog food. The most common food allergies are to common pet food ingredients that the pet has been eating for a long time - beef, dairy products and wheat in dogs; beef, dairy products and fish in cats.
Items in the dog or cat food that trigger allergies are not always listed on the label. Is the calcium source of the food beef or pork bones? What kind of vegetable oil was sprayed on the food during processing to prevent the nuggets from sticking? Were the poultry by-products chicken or turkey? Reading labels on pet food and trying to find a diet that doesn't have the same ingredients on the label as the current food you are feeding usually doesn't work. There are too many ingredients common from food to food and too many possibilities that aren't clear on the label.
Food allergy symptoms are the same symptoms we see with other illnesses. Fleas, mites, inhalant allergies and bacterial infections all cause similar skin symptoms. Infections, parasites, ulcers, cancer and other diseases all can cause similar gastrointestinal signs. There is no blood or skin or stool test we can do as yet that will wave a red flag and say 'Hi. I'm a food allergy.' The only reliable diagnostic test we have is the hypoallergenic food trial.
To diagnose food allergy, your veterinarian will put the pet on a food trial, meaning a diet specially made to avoid an allergic response by the pet's immune system. It takes anywhere from 1 to 12 weeks for the allergens that have accumulated with time to work out of the system and for the allergic reaction to die down. After that happens, if the pet indeed has food allergies, you usually see dramatic improvement in the signs or symptoms of the disease. If a pet has been on a hypoallergenic food trial for 10-12 weeks (longer for skin problems, shorter for intestinal problems) and you have seen no improvement in signs, the pet's condition is probably not being caused by food allergy.
In the past, a hypoallergenic diet was one that contained novel ingredients - ingredients the pet had never eaten before and thus had not built up any allergy to. These diets are made of protein sources such as duck or venison instead of the usual pet food ingredients like beef or chicken. We did not start feeding a pet one of these diets until the signs of allergy had been present for at least 6 months, to avoid having the pet develop allergies to the new diet just as he had the old one. Remember, the dog or cat can become allergic to anything during that initial 6 months when it is developing the allergies. We would use this initial 6 months to treat for and rule out other causes of the symptoms the pet owner was seeing. During this 6 months veterinarians advised feeding the pet one brand of food only, and to minimize exposure to table food and other items. This would limit the number of items your pet could become allergic to.
This still may be the protocol for some allergic pets, especially ones who have had symptoms for over 6 months. However, a new technology in food processing has produced a new type of hypoallergenic diet that is safe to put pets on even in the early stages of developing allergies to food. It also should be more effective than the novel protein diets we've had in the past. This new diet is called Z/D and it’s made by Hill's, the company that also makes Science Diet products.
Z/D is made of very short-chain protein molecules. The proteins in the food have been broken up into pieces smaller than the minimum size required to cause an immune reaction. Carbohydrate sources such as rice, wheat and corn contain protein as well as do ingredients that are actual meat. It's usually the proteins in the diet that trigger food allergy reactions. In Z/D both the animal and plant proteins in the food have been broken down into small pieces to make them less stimulating to the immune system, thus preventing an allergic response by the pet.
You must feed the special Z/D or other hypoallergenic food for at least several months before deciding that it is or is not working. If symptoms improve quickly on the new food, great, you've made a diagnosis. If it takes longer, hang in there and don't stop too soon. Feed the new diet for as long as it takes to know for sure.
During the diet trial you must do your absolute best to ensure the hypoallergenic diet is the only thing your pet eats. The more scavenging your pet does the longer it usually takes to see response to the trial and the less sure you'll be of a diagnosis.
This means:
*No treats, chewies, biscuits, bones, rawhides or snacks.
*No chewable or flavored heartworm pills, vitamins, mineral supplements or other flavored medications. You will need to use non-chewable or unflavored ones.
*No fatty acid supplements (they contain fish oil and come in a gelatin capsule made of animal by-products).
*No flavored toothpastes (use baking soda to brush your pet's teeth).
*No table food, no sneaking cat food, no cat poop from the litter box, no going outside to hunt mice, no scavenging the compost pile, no licking plates or wrappers and no licking the floor! If you drop a food morsel, try to pick it up before the dog gets it. If your baby throws food to the dog, lock the dog in another room or kennel him at mealtimes.
You will be spending a lot of time, money and effort on your pet to do this food trial. Realize it is an expensive diagnostic test that needs to be done properly if it is to work. Don't skimp. It will seem like the biggest pain you could imagine while you are doing it, but in the big scheme of things, the 4 or 8 or 10 weeks it takes is not really such a lot of time.
WHAT HAPPENS AFTER YOU GET THROUGH THE TRIAL??
If your pet's symptoms improve on the hypoallergenic diet trial, you have 2 choices. You can continue the Z/D or other special diet. Or you can introduce other diets, treats or medications slowly, one at a time, in an attempt to determine which ingredient is the culprit. If the symptoms recur you then know which things to avoid and which he or she will tolerate. For big dogs, especially, the Z/D is expensive to feed. You can try a less expensive alternative - another version of Z/D that is not so processed or another commercial hypoallergenic diet, and see if the symptoms remain controlled. (If after 10-12 weeks of a strict diet trial your pet's symptoms have not improved that means your pet does not have a food allergy. Other tests may then be needed for diagnosis.)
Upon re-exposure to a substance the dog or cat is allergic to, symptoms will recur anywhere from 1 hour to two weeks later. Some owners notice a dramatic return of signs the first time the dog gets a few corn chips off the floor or the cat gets a bit of tuna. You must give any new ingredient or food two weeks before deciding if it is safe to feed it long term. If your pet does start to worsen again, immediately reinstate the hypoallergenic diet or discontinue the culprit item. If you catch it early, the reaction will usually die back down in a week or so, and then you can try again with a new food or item. Remember that if your pet has not been showing symptoms for at least 6 months it is not a good idea to introduce any new foods or medications - the pet may still be in the stage of developing more allergies and he will simply become sensitized to the new items you've added in. Wait at least 6 months before trying any new or re-introduced products on a food-allergic pet!
If you are looking for a less expensive alternative to Z/D, and your pet has never eaten a lamb based diet before, your veterinarian may recommend a lamb based commercial diet to try, as these are now readily available. If you feed this new diet for two weeks and signs do not recur, it is probably safe to feed it long term. Remember, it is rare for an animal to develop additional food allergies once the initial 6 month sensitization period is over. If the pet has eaten lamb before, there are hypoallergenic diets available made of venison and potato, fish and potato, duck and potato or rabbit and potato. Most pets (about 90%) will tolerate these.
It is not necessary to prove every item the pet is allergic to by introducing individual ingredients back every two weeks to see which ones make the pet sick. Your goal is usually to make your pet feel better. If you find a food the pet tolerates, you can just keep feeding it forever. If needed, other medications and supplements can be introduced back one at a time to determine if the pet can tolerate them. If your dog seemed fine on its new commercial diet but got itchy a week after he got his chewable, beef flavored heartworm pill, you'll have to stick with the non-chewable kind. If your cat was fine until he licked the cereal bowl don't ever give him milk products again (including cheese). Remember, one item at a time, then wait two weeks before trying another.
The hard part here is that flea or pollen allergies may cause itching as well as food allergies. Viruses and parasites cause diarrhea just as food allergies do. There may be more than one disease process going on in a pet to cause symptoms and telling which is what can be difficult. This is where we can help. Your veterinary team is available to help you throughout the food trial and afterwards. Success at controlling symptoms requires a good doctor-staff-client team. Please call your veterinarian with questions at any time!
