usually you start out with a limited ingredient food. I know of greys that were not truly allergic to the food but the dye/coloring used in the food.....Many blame soy, some grains for the allergies. I have used limited ingredint food for a cat, started with duck/pea. There are a few brands that make such diets. Some are sold through vets office. If it would be one of my greys I would probably try one of the 'natural/holistic' types, I know there is a bison based food, a couple of no or very limited grain foods in dry and canned form available. I can search for a few brands if you need more info but you also need to check what is availble in your area. Other option is to switch to a raw or homemade diet, heavy on meat protein - starting with one type of meat and maybe one grain like barley or some less commonly used grain in petfood and maybe one veggie. If it seems to work, you can - after a while - slowly add one different thing at a time. If the dog develops symptoms, at least you know what the most likely culprit is. First I would cut out all food/treats with food coloring and preservativestoo. I think Evo makes a good food with high meat/limited grain, ? Call of the Wild has a bison based food, Solid Gold has a couple possible choices but I can't remember all the brands of the top of my head......Good luck, do you have retired racers?