Wild caught fish oils serve as the best sources of Omega 3 fatty acids for dogs and cats. While flax oil is also rich in Omega 3s, it is not a complete source. Why? Because the Alpha-linolenic acid, (ALA) in flax oil does not convert to docosahexaenoic acid (DHA) at levels that confer any physiological benefit--- and studies show that EPA conversion is deficient too. Plus, most holistic veterinarians agree that dogs, cats and other carnivores are naturally set up to metabolize most of the essential fatty acids they need from meats and animal fats - not from vegetable oils.