[grumpy old mare]

Well, if you're going to take him to the vet anyway for the next set vaccinations, maybe you can ask him/her about the sensitive skin/upset tummy thing - or has that totally stopped with the new corn-free food anyway? If it has - then just stay clear of anything with corn in it (better no 'ready made' treats either, as loads of them contain all sorts of junk  []) and "bob's your uncle".

 [:X]