Food allergies may be the source of your dog or cat’s chronic GI issues, skin itchiness, and frequent ear infections. In this article for “Asthma & Allergies Awareness Month” for May, The Meowing Vet dispels commonly held misconceptions about canine and feline food allergies, discusses the most common allergens (likely not the ones you’re thinking about), and teaches pet owners how to manage nutritionally-balanced feeding plans for affected dogs and cats.
Read on…
What is a food allergy?
A food allergy (or food hypersensitivity) is an adverse response of the immune system to an ingested molecule (typically a protein) found in a food source. This hypersensitive immune response triggers a cascade of events that falsely tells the body that it is being invaded by a harmful substance (in this case, the food allergen). This in turn leads to the release of inflammatory products (such as histamine) that cause GI upset and skin itching. This overactive immunological reaction occurs due to a disruption in the natural defense systems of the GI tract, including abnormalities in normal digestion (impairment of certain acids, enzymes, and bile salts), inflammation of the gut lining, or dysfunction of T-cell antibody regulation (gastrointestinal associated lymphoid tissue, or GALT).
Most allergens (i.e. food allergy triggers) are proteins of a particular size (mostly between 10,000-70,000 Daltons, a type of molecular measurement). Smaller proteins (<5,000 Daltons) are less likely to stimulate an inappropriate immunological response that perpetuates the adverse signs of food allergies. Therefore, smaller proteins may be part of a “hypoallergenic diet,” as discussed in greater detail below.
FACT: Any dog or cat of any age, either male or female, and any breed can be affected by food allergies. 20-30% of pets with food allergies have other types of hypersensitivities (such as allergic responses to fleas, grass, chemical exposure, etc.).
MYTH: Carbohydrates and chicken are the most common causes of food allergies in pets.
Proteins are much more likely than a carbohydrate to be the culprit behind your dog or cat’s food allergy. And of the protein sources, beef and dairy products are the most common causes of food allergies in pets. Chicken has only been shown to be a trigger in roughly 25% of dogs with food allergies and is less likely to be of concern in cats with dietary sensitivities. So before you avoid chicken and corn (as well as other grains) altogether, remember that they’re not always bad. Your vet will aid you in discovering the trigger of your pet’s food allergy, which may not be the ingredient of which you’re suspicious.
(FYI: Corn is not a dog food filler. It is a nutritionally-dense source of energy, protein, and carbohydrate that is beneficial for your dog. The same goes for gluten: gluten is a natural protein found in wheat, and gluten-intolerance/celiac disease is not common in companion animals. Unless your dog has a food allergy to corn or wheat, these ingredients need not be avoided when they’re part of a balanced diet.)
Other more common causes of food allergies in pets include other meat and seafood sources and occasional grain proteins (such as those found in wheat, corn, and soy). The breakdown of the dietary trigger behind food allergy cases by species is as follows:
| Dogs | Cats |
| 65% of food allergy cases:
· Beef · Dairy Products · Wheat |
80% of food allergy cases:
· Beef · Dairy Products · Fish |
| 25% of food allergy cases:
· Chicken · Chicken eggs · Lamb · Soy |
Less common cause of food allergy:
· Chicken
|
| Rare causes of food allergy:
· Corn · Pork · Rice · Fish · Food Additives |
|
MYTH: Food allergies are a very common cause of skin itchiness among dogs and cats.
This one’s sort of a trick question. Only about 1-10% of cases of itchy skin (or pruritus) stem from food allergies; another disorder is behind the other 90-99% of cases. Therefore, chances are that a condition other than a food allergy is the cause of your pet’s itchy skin. However… nearly 100% of all pets that have a food allergy will have pruritic (itchy) skin.
Other dermal issues associated with food allergies include skin redness (erythema) and skin infection (pyoderma). Hives (urticaria) are also possible but less likely to develop. You may also notice tiny raised “bumps” on your cat’s skin, known as miliary dermatitis. The most severely affected skin regions include the face, feet, armpits (axilla), base of the tail, and rear (perianal dermatitis and anal sac issues are typical). Due to constant and aggressive scratching to alleviate itchiness, your pet may cause self-traumatized skin abrasions with areas of hair loss (alopecia) and secondary bacterial infections of the skin. Frequent ear infections (otitis externa) are also possible.
Cats may also develop eosinophilic plaques and granulomas, which are itchy and oftentimes painful skin lesions that can occur around the abdomen or mouth. (FYI: Eosinophils are specialized white blood cells often produced in the face of allergic reactions, including asthma.)
FACT: Nearly 10-15% of dogs with food allergies will have gastrointestinal problems, including intermittent or more chronic vomiting or diarrhea (including soft stools and increased defecation frequency). Increased gastrointestinal sounds (borborygmi, or a “growling stomach”) can also occur. Cats with food allergies are less likely than dogs to have GI signs and more likely to have dermatological issues.
MYTH: Inflammatory bowel disease (IBD) and food allergies are the same thing.
IBD is a much more severe disorder and occurs due to a combination of not only an exaggerated immune response but also abnormal lining of the intestinal tract. IBD typically results in worse gastrointestinal signs in affected dogs and cats, which can progress to significant weight loss, decreased appetite, and fever. The management of IBD is similar to that of food allergies in part as both disorders involve use of a hypoallergenic diet. However, oral anti-inflammatory steroid therapy is also a component of IBD management.
Visit The Meowing Vet’s website later on for a future article on Inflammatory Bowel Disease (IBD).
MYTH: Immediate GI upset after consuming a brand new food source following a recent dietary change means that a dog or cat has a food allergy to the new ingredients.
Vomiting or diarrhea very soon after your pet ingests a new food is more likely to be caused by food intolerance, meaning reactions against food products not involving the immune system. The most common types of food intolerance include dietary indiscretion (such as eating too much, ingesting a foreign body, or consuming rich or spoiled foods) or food poisoning.
On the other hand, a food allergy requires time to develop. The immune system needs steady exposure to a food ingredient to “amp-up” (i.e. become hyper-sensitive) to that ingredient in order to one day react negatively to such food. This immune system reaction often takes months or even years to occur before your pet begins showing signs of having a food allergy. Many pet owners do not consider the possibility of a food allergy to be behind their pets’ new skin and GI issues since they’ve always fed the exact same pet food for years. However, as explained, pets can develop a new food allergy to a commercial diet they’ve eaten all their lives. Feeding a dog or cat with a food sensitivity a new diet containing solely new ingredients (or novel proteins) can eliminate this over-exaggerated response by the immune system and alleviate the signs of food allergy. (Learn more about novel proteins below.)
Refresh your knowledge regarding human foods that are toxic to dogs and cats by clicking here.
And click here to learn the most common causes of canine vomiting.
MYTH: Food allergies are easy to diagnose.
Oh, how I wish this were true. Much to the aggravation of veterinarians and pet owners alike, the assumption that food allergies are simple to diagnose is false. Properly diagnosing a true food allergy can be a long, convoluted process. Food allergies are often a diagnosis of exclusion, meaning that other more common causes of non-seasonal skin and GI issues are ruled out first before suspecting the possibility of a food allergy. Atopic dermatitis, flea allergies, sarcoptic mange infestations (scabies), and contact allergies in dogs must be investigated via diagnostic testing prior to considering a food allergy. Diagnostic rule-outs to consider in cats include atopic dermatitis, demodectic or notoedric mange mites, flea allergies, and fungal ringworm.
MYTH: Allergy testing, involving either skin testing or blood serology, is an accurate way of assessing food allergies in my pet.
Unfortunately, allergy testing in veterinary medicine currently has little reliability for diagnosing food allergies and is often a waste of time and resources. If your pet tests negative for a certain allergen, then he or she is unlikely to have a food allergy against that product. However, just because your dog or cat tests positive for another allergen does not necessarily mean that product is the cause of your pet’s skin and GI disorders. Falsely positive test results may occur, negating the value of such allergy testing.
FACT: A food elimination trial is the best way to test for a food allergy.
No treats or table scraps should be fed during the 8-week food elimination trial.
If your pet has a suspected food allergy, and all other causes of the skin and GI issues have been ruled out, a strict food elimination trial is the next best step. This dietary trial means feeding a strict diet for at least 8 weeks using only ingredients to which your dog or cat has not been exposed in the past. This means a diet free of flavoring additives and preservatives with no treats or table scraps, no chewable medications (which may contain flavorings), and no flavored toothpaste. While a homemade diet may be formulated, it is both time-consuming and may not be nutritionally balanced. Therefore, a pet owner’s best option typically includes a hypoallergenic prescription veterinary diet (see options below).
Rechecks with your veterinarian at 4 and 8 weeks are advised to allow your vet to monitor your pet’s skin improvement as well as discuss your at-home findings. Pet owners are encouraged to keep a diary to track their dog or cat’s skin and GI health while on the new diet (exactly what foods are fed, how often the pet scratches, appearance of stools, etc.). Pets with food allergies typically show at least a 50% improvement in skin and gastrointestinal quality after 4 weeks on the new diet.
After the 8-week period of time is over (during which time your pet should have hopefully improved significantly if a food allergy is the indeed the culprit for the previous clinical signs), a dietary challenge is requested. A dietary challenge is accomplished by re-feeding your pet’s original commercial diet for 1-2 weeks. If your pet’s skin and GI problems return following consumption of their old pet food, then there is no doubt that he or she is allergic to something in the original formula, and the food elimination trial is started yet again. Many pet owners are hesitant to perform a dietary challenge since they fear the return of their pet’s itching and loose stools. However, a dietary challenge is important in reaching a concrete rather than suspected diagnosis of a food allergy.
How? For instance, what if your dog or cat actually had an allergy to flower pollen rather than food and started showing hypersensitivity signs in late Spring (dermatological signs when the pollen came in contact with the skin and gastrointestinal effects when your pet licked his paws and ingested some pollen from his fur). These signs may be identical to those displayed in pets with food allergies, so a food elimination trial is performed for 8 weeks, at the end of which your pet seems back to normal. You and your vet assume that since the pet improved, a food allergy was to blame. But this is only by coincidence; the flowering plant stopped blooming during this two-month period of time as the season changed, so your pet is no longer exposed to the inciting pollen. If you choose not to perform a dietary challenge, then you will falsely assume that your pet has a food allergy, causing you to spend unnecessary funds on an unnecessary hypoallergenic diet. Come next Spring when your pet is once again in contact with the pollen, his clinical signs will return, leaving you and your vet puzzled. If you had not declined the dietary challenge last year, you would have seen that your pet’s skin and GI problems did not return when his original diet was fed, alerting you to the need to continue with different diagnostics to discover the root of the allergy. Therefore, a dietary challenge is very important in definitively diagnosing your pet’s food allergy.
An alternative to the dietary challenge is a more tedious yet more accurate tool: the provocation test. A provocation test involves making a list of all the ingredients in your pet’s original commercial dog or cat food. You then feed your pet only one of the ingredients found in the original food for two weeks at a time before feeding another of the ingredients… and so on. Once the pet’s skin or GI tract reacts negatively to the particular ingredient being fed, then that ingredient can be accurately identified as the cause of the animal’s allergic response. By discovering the specific ingredient driving your pet’s food allergy rather than just avoiding a commercial diet altogether, you may have more options in developing a less strict feeding plan for your dog or cat.
Click here to learn about the nutrient requirements of dogs and cats and the pros and cons of homemade, raw, and vegetarian diets.
MYTH: Pet owners don’t have many dietary options for managing a pet’s food allergy.
Fortunately, modern day veterinary nutrition has allowed for a bigger variety of diets for dogs and cats plagued by food allergies. Nutritional experts specially formulate hypoallergenic prescription veterinary diets to provide for your pet’s nutritional requirements while living up to the name “hypoallergenic” (meaning unlikely to trigger an allergic reaction when ingested). Canned foods and dry food options are available, and some manufacturers may even offer hypoallergenic treats that won’t cause an unwanted allergic response. The two main dietary strategies of managing food allergies are either a novel protein or modified (hydrolyzed) protein diet.
- a novel protein and novel carbohydrate diet: involves feeding a single protein and carbohydrate source to which your dog or cat has never been fed before
- Common novel protein options: rabbit, duck, kangaroo, venison, buffalo, fish
- Common novel carb options: potatoes, oats, barley
- Prescription veterinary diet examples:
- Hill’s® Prescription Diet® d/d®: for dogs (duck, salmon, or venison with potato; lamb and rice; egg and rice); for cats (rabbit, duck, or venison with green pea)
- Purina® DRM®: for dogs (rice, salmin, trout)
- Iams® Veterinary Formulas® Skin & Coat Response®: for dogs (either fish and potato or kangaroo and oats); for cats (lamb and barley)
- Royal Canin®: for dogs (duck, rabbit, venison or white fish with potato; vegetarian option with potato); for cats (rabbit, duck, or venison with peas)
- a modified protein diet: primarily means use of a hydrolyzed protein source and a novel or refined carbohydrate (such as rice or a starch, respectively)
- A hydrolyzed protein is made of highly digestible protein sub-pieces of small molecular size (often <5,000 Daltons, making it less likely to trigger a hypersensitive allergic immune response).
- Issues with hydrolyzed protein diets may include expense, lower energy quality (which can cause unwanted weight loss), and poor taste of some products.
- Prescription veterinary diet examples:
- Hill’s® Prescription Diet® z/d®: for dogs and cats (hydrolyzed chicken liver)
- Purina® HA®: for dogs (hydrolyzed soy protein); for cats (hydrolyzed soy protein and chicken liver)
Royal Canin®: Hypoallergenic HP® formula for dogs and cats (soy protein isolate); Anallergenic® formula for dogs (bird feathers and corn starch)
Always check with your personal veterinarian for the latest hypoallergenic products on the market in your specific country. Your vet can create an individualized dietary plan for your dog or cat and advise you on which prescription brand and formula is best for your pet.
FACT: While not curable, food allergies carry a good prognosis with proper management, which involves strict avoidance of known dietary allergens. To reiterate, this means no outside treats or human foods and may even involve switching your pet from an oral chewable flea, tick, and heartworm preventive to a topical formulation.
Now that The Meowing Vet has exposed the myths and stated the facts of canine and feline Food Allergies, with the assistance of your vet you’ll be able to expertly manage your pet’s dietary requirements to alleviate the side effects of those pesky food sensitivities.
– Maranda Elswick, DVM
