
Mmmmmmmmm,
Having not seen your dog, i am wary about this, but, from what you say, i highly suspect that he is lacking something in his diet.
IF he was mine, then i would be adding foods carefully to his diet.
Do you feed the mince raw? If not, i would start doing so, as he can gain far more nutrients from it raw, than he can cooked. If you are feeding cooked, just cook it a little less each day until you are feeding it totally raw.
I would then add vegetables, probably best if you need to limit the variety till you can pinpoint the cause of the colitis, just give him carrot, spinach, mmmm, and celery. Blend it up in a food mixer till it resembles, urr, vomit!!!!!
If he is fine with that, then you can gradually add more vegetables. You only need to feed about a tablespoon a day, too much and your dog WILL get the runs!!!!!! If just those three veg bring back the colitis, pick just one, and feed that, if its fine, add another, and so on, until he has a variety of veg.
The best meat really is chicken, (something to do with the right levels of fats and amino acids or soemthing, but it is nearly 3 am, an i cant recall just now).
Definately go back to your vet, and ask him again about your dogs diet, as no dog should be fed just meat for any length of time. Dogs, like man are omnivores, they need a variety of meat and vegetables to be healthy.
Good luck with him.
Em