Hi CYNDEAN and Welcome!
These are a few items in dog food AND treats that dogs are sensitive to: Chicken Items (Meat, Meal, Fat, Eggs, Cartilage) Grains of all kinds (including oatmeal and oatmeal shampoo!), even some of the "Non-Gluten" grains, Lentils/Pea items, Potatoes, Flax seed or oil, certain Fish and Yeast supplements. So read the ingredient list VERY carefully.
Diamond Grain Free Salmon (1st 10 ingredients): Whitefish, fish meal(WHAT fish??? Source is UN-Named. Could contain Ethoxyquine!)
, sweet potatoes, peas, lentils, pea flour, canola oil (preserved with mixed tocopherols), tomato pomace, flaxseed,
natural flavor, salt,
Diamond Grain Free Beef (1st 10 ingredients): Beef, lamb meal, sweet potatoes, peas, lentils, pea flour, canola oil (preserved with mixed tocopherols), tomato pomace, flaxseed, fish meal (WHAT fish???Source is UN-Named. Could contain Ethoxyquine!)
Common thread between the 2 Diamond products you are feeding is Flax and Fish Meal, which is an UN-Named source of fish.
I would slowly switch to a high quality - ONE PROTEIN Limited food like ACANA SINGLES with a matching 1 protein treat and......NOTHING ELSE (NO cheating ) for a 6 to 10 week trial period.
Acana Limited “Singles”: Pork & Butternut Squash: http://acana.com/our-foods/singles/p...ternut-squash/
Ingredients: Deboned pork*, pork meal, green lentils, red lentils, pork liver*, butternut squash*, pork fat, green peas, yellow peas, canola oil, algae, garbanzo beans, pumpkin*, carrots*, pork kidney*, freeze-dried pork liver, kelp, chicory root, ginger root, peppermint leaf, lemon balm, mixed tocopherols (preservative), dried Enterococcus faecium fermentation product.
Pork & Squash Limited treats: https://acana.com/our-foods/dog-food...uash/?lang=usa
Store locator: Store Locator | Acana
Nature's Variety also makes a Limited Kibble but their treats have contain flax so I wouldn't use the treats Here is a sample:
Nature's Variety "Instinct" Limited
not Nature's Recipe): Limited Ingredient Lamb: (can be purchased at PetsMart, Petco) Instinct Grain-Free Limited Ingredient Kibble Dog Food - Lamb | Instinct Pet Food for Dogs and Cats
Ingredients: Lamb Meal, Peas, Tapioca, Pea Protein, Canola Oil (preserved with Mixed Tocopherols and Citric Acid), Lamb, Natural Flavor, Montmorillonite Clay, Coconut Oil, Potassium Chloride, Salt, Choline Chloride, Vitamins (Vitamin A Supplement, Vitamin D3 Supplement, Vitamin E Supplement, Niacin Supplement, L-Ascorbyl-2-Polyphosphate, d-Calcium Pantothenate, Thiamine Mononitrate, Pyridoxine Hydrochloride, Riboflavin Supplement, Folic Acid, Biotin, Vitamin B12 Supplement), Minerals (Zinc Proteinate, Iron Proteinate, Copper Proteinate, Manganese Proteinate, Ethylenediamine Dihydriodide, Sodium Selenite), Green Tea Extract, Rosemary Extract
Store locator: Find A Store | Nature's Variety
1 Ingredient Lamb treats: http://www.purebites.com/en/products/dog/freeze-dried/lamb/