If you have a dog with a food allergy, you know how difficult it can be to diagnose. It sounds simple enough: Feed the dog a food that does not contain his allergic triggers and monitor for changes in his clinical signs.
The most common symptoms associated with food allergies in dogs are itching and chronic or recurrent skin and ear infections. Some food allergic dogs also suffer from loose stools and/or vomiting. If during the food trial a dog’s symptoms disappear or at least get much better (some food allergic dogs also have environmental allergies), you’ve got your diagnosis.
Easy, right? Not so fast.
Food trials can take a long time to complete. Six to eight weeks is typical, but I’ve gone as far as 16 weeks before calling it quits. During that time, dogs have to eat ABSOLUTELY nothing but the recommended hypoallergenic food. No treats, table scraps, flavored medications; nothing else but water.
And determining what exactly is hypoallergenic for a particular individual is not always a straightforward process. Most dogs are allergic to the protein sources in their foods. Therefore, we need to find a food that contains only novel protein sources (i.e., ones they have never eaten before) or proteins that have been modified so they are no longer allergenic. Carbohydrate sources are a less frequent but not negligible source of allergens, so hypoallergenic diets typically either contain rice, to which most dogs don’t react, or novel ingredients like potato.
To top it all off, prescription hypoallergenic diets for dogs are not cheap. My boxer, Apollo, has to eat one that runs around $100 per 32 pound bag. Good thing I love you, boy.
In an attempt to simplify and reduce the costs of a food trial, owners frequently ask, "Isn’t there an over-the-counter food we could use?" This is a reasonable question given that a walk down the pet food aisle will turn up products made from venison and sweet potato, and other such appropriate-sounding combinations. Unfortunately, there are two good reasons why the answer to this question has to be "no."
1. Closer inspection of the ingredient list often reveals the presence of ingredients that aren’t advertised on the front of the bag. I looked at the label of one over-the-counter (OTC) "venison and potato" food and found that chicken, fish, and egg were also included in the diet.
2. Even if you find an OTC food containing only protein and carbohydrate sources that are similar to those included in a prescription hypoallergenic diet, the OTC food might be contaminated with other ingredients. A study published in 2011 in the Journal of Animal Physiology and Animal Nutrition revealed that "Three of the four over-the-counter (OTC) venison canine dry foods with no soy products named in the ingredient list were ELISA positive for soy; additionally, one OTC diet tested positive for beef protein with no beef products listed as an ingredient..."
I wouldn’t expect similar findings with prescription diets since quality control measures should be much tighter.
Once a food allergy has been diagnosed and the offending ingredient(s) identified (by sequentially reintroducing potential offenders and monitoring for a relapse of symptoms), over-the-counter products may be an option for maintenance. For example, if you know that your dog is allergic to beef, any high quality food that provides balanced nutrition without the inclusion of beef would be appropriate. But, if your dog’s symptoms return, I’d be suspicious that cross contamination might be to blame. In these cases, switching to another OTC food with an appropriate ingredient list or going back to a prescription diet would both be reasonable options.
Dr. Jennifer Coates