Hi Jaz, I have had dogs forever it seems like, and have done quite a bit of research on dog food, just for my own feeding. Since it is lots and lots of material I have, I will go though some of it later and get back to you, because I am pretty sure I read about special food for giant breeds with sensetive stomachs. One thing you can do in the meantime though, is to give a bit of peptobismuth, you know the pink thing you take yourself when you have an upset stomach, it is totaly harmless and you can either give the liquid, but they have tabs. which I find easier to use. Depending on his weight, dose it as you would a human with similar weight, it it is a food allergy it wont cure it, but until you have found a good way to feed him, it may help the loose stool. Mind you I will go though all my papers and see if I cant find the one I am pretty sure I have on the subject.
Marit