Dr. Mona Miller lives in Lafayette with her young son and two cats. She has worked at Four Seasons Animal Hospital in Lafayette since moving here in 2001. She attended Cal as an undergrad, and received her DVM from U.C. Davis. She can be reached at Four Seasons, 938-7700, or by email to MonaSDVM@aol.com.

With few exceptions, there is nothing inherent in a food source that makes it good or bad for a species. Just as some individual humans have dietary intolerances (lactose, gluten, etc), so do individual animals. Likewise, some individuals can eat all varieties of foods, no matter the fat or spice content, and have no trouble with digestion. I keep in mind whether the individual is experiencing any symptoms that might be related to food intolerance before calling it "good" or "bad" for that particular pet. For instance, from a physiologic standpoint (leaving out cultural or ethical issues, and I'm willing to risk some raised eyebrows here) there is nothing "better" about a grain-free diet as a general diet for an entire group/species.

Some disorders may call for a trial change in diet to determine if symptoms resolve. The main culprits in food intolerance are usually the protein and/or carbohydrate source, rather than preservatives, vitamins or minerals. Food trials are important for food allergy problems manifesting as chronic itchy skin and ear inflammation, and for intestinal intolerance manifesting as stomach noises, flatulence, vomit or diarrhea.

There are three main factors to consider when changing a food for a trial: the ingredients of the diet, the length of time feeding the new diet and awareness of all foods entering the animal's mouth. This takes real commitment involved on the part of the pet owner, as you will read. I like to have an in-depth conversation with my clients before starting a food trial so that all factors are understood.

When changing the protein or carbohydrate ingredients, one must change ALL the ingredients. To do so, you should read the entire list on the back of the bag or can. For example, let's say that Diet A states "lamb and rice" on the front label but actually contains lamb, rice, soy, chicken and egg as stated in the ingredient list. Diet B states "venison and potato" on the front label and contains venison, potato, lamb, soy and egg on the ingredient list. A change from Diet A to Diet B will still provide exposure to lamb, soy and egg; thus the entire diet hasn't actually changed. This is often where veterinary prescription diets come in handy - because these are formulated to be limited in the ingredients to just a couple of food sources.

For a dog, it is recommended to feed a new diet for six to ten weeks before deciding its effectiveness; and four to eight weeks for a cat. In a true food trial, one should follow this time frame with a challenge of the previously-fed food for a couple weeks to determine if the symptoms return.

ALL food that goes into the pet's mouth should be considered when changing to a limited ingredient trial. This includes dry, can, dog cookies, cat treats and table scraps. Even indigestible items that can still provide allergens might need to be excluded, such as Greenies and rawhide chews.