My son has a mongrel, a dalmation/boxer cross. He started scratching and constantly nibbling away at his paws when he was about a year old. After lots of expensive tests at the vets it was discovered he has allergies, mostly to meat(!) but also dairy products and to grass/pollen etc. As a result he is on a special diet which doesn't contain any meat except lamb and the vet suggested he wasn't taken for walks where there is grass, particularly in the summer months(!) He has to have steriod tablets and injections given by my son. But he is great now, though he does still have times when he nibbles away at his paws. We have to watch carefully what he eats, he isn't able to have any usual doggy treats, it is really difficult to get vegetarian dog stuff!