Hya just an idea if he gets fed up with chicken and rice, you could try alternating it with boiled white fish and rice, When Minstrel had colitis he was prescribed Insulox (sp/) tablets and they seemed to do the trick quite quickly - but do finish the course...or symptoms my return.
I imagine you got Prokolin too, I always keep a tube of this in the cupboard, it works great if dog's tums are upset.
Hope he feels better really soon