Mmmm. Hund n Flocken is a lamb based food. That's not quite so helpful as if it had been a chicken one, for example. Then we could have suspected turkey as the cause... LOL - life is rarely so nice and simple though.
Anyway. Comparing the two foods he's been on lately:
EVO ingredients:
Turkey, Chicken, Turkey Meal, Chicken Meal, Potatoes, Herring Meal, Chicken Fat, Natural Flavors, Egg, Garlic, Apples, Carrots, Tomatoes, Cottage Cheese, Alfalfa Sprouts, Dried Chicory Root, Taurine, Lecithin, Rosemary Extract, Vitamins/Minerals, Viable Naturally Occurring Microorganisms
Hund n Flocken ingredients:
Lamb | Lamb Meal | Millet | Brown Rice | Cracked Pearled Barley | Oatmeal | Rice Bran | Menhaden Fish Meal | Canola Oil | Flax Meal | Amaranth | Blueberries | Dried Chicory Root | Carotene | Choline Chloride | Vitamin E Supplement | Iron Proteinate | Zinc Proteinate | Yucca Schidigera Extract | Copper Proteinate | Manganese Proteinate | Potassium Iodide | Thiamine Mononitrate | Ascorbic Acid | Vitamin A Supplement | Biotin | Calcium Panthothenate | Sodium Selenite | Pyridoxine Hydrochloride | Vitamin B12 Supplement | Riboflavin | Vitamin D Supplement | Folic Acid |
That actually generates quite a number of possibilities. Actually all of the ingredients in the EVO... since none of them are also in Hund n Flocken.
Still, some of those are more likely than others to be the cause. The two poultry ingredients have to be considered as likely causes, as would be the cottage cheese and eggs (dairy). While it is possible that the fruits/vegetables could be what's causing the problem, it's less likely than those other ingredients. Herring meal is also a possibility, but is the least likely since there was a fish meal in the Solid Gold and he had no issues with that.
Sooo. What to do with all of that? One obvious solution is reverting to the Hund n Flocken, since you know he's OK with that. But that leaves you without any knowledge of what in the EVO was causing the problem, and what you can safely feed in the future.
I think if it were me, I'd probably try him on a food that did include chicken (or turkey, but not both), and as few other common ingredients with EVO as possible. See whether the problem clears up. If it does, then you know it's not chicken that's the problem (which is certainly worth knowing, because chicken is the most common meat used in dog food). And if the problem doesn't clear up, then you know that chicken at least is a meat you'll have to avoid - with question marks remaining over turkey (though it's rare to find a food that has turkey without chicken - so if chicken is a problem, you can pretty much forget about feeding turkey too).
How about trying California Natural Chicken formula? Doesn't have to be long term, but it would certainly help to identify whether or not chicken is a problem for your boy. That is an allergy food that has very few ingredients - basically it is chicken, rice and oil. You already know rice isn't a problem, since he had that in the Solid gold. So if he has continued itching problems on Cal. Natural, you'd know with reasonable certainty that your dog is allergic to chicken (and if he is, then there are plenty of alternative suggestions we could make on high quality food options).
If he doesn't have any problems with the CN - then great, chicken isn't the cause. That would be a good time to try a different chicken/turkey based food to see about the turkey aspect of things.