
My dogs do fine on Arden Grange. In fact, they do fine with any food in terms of allergies. So the experience of others really does not matter much when it comes to figuring out why your dogs are suddenly itchy!
If you think it's the food than compare the ingredients of Nutro and Arden Grange and figure out what may be in Arden Grange that is not in Nutro. Or, look to see where Arden Grange might have more of some food than Nutro. That should help you determine if food is the likely cause; apart from the thousand other things that can cause allergic reactions inside and outside the house.
Still not happy, go back to Nutro and if your dogs symptoms disappear within a month than it may have been Arden Grange. (Or, it may have been a pollen or mold outside that died off because of the change in outside temperature over that month too!) So frustrating, isn't it?