A raw diet contains many of these, but supplementing the diet can also help. Vitamin C and E are two very well known antioxidants. Minerals like selenium and zinc boost the immune system too. Check with a doctor about proper supplementation, or simply includelots of foods that contain natural selenium and zinc. Flavonoids are found in many things, such as grape seed extract, pine bark extract, green tea and Gingko biloba.
Astragalus is a wonderful herb for treating many immune system problems, including allergies.
NAET is a technique that has been used very successfully in treating allergies. Well, most grains, yeast, dairy products, legumes like soybeans, as well as molds and spores and any variety or chemicals, such as lawn fertilizers, carpet cleaners or laundry detergents. An animal may also be allergic to a beef-based kibble but do fine on raw beef. Your animal is designed to eat raw meat and therefore anything that isn't a species-specific food is potentially an allergen. This is why it is important that you feed your animal a diet that is appropriate for them.