what are you feeding him? How much fruits and vegetables are you feeding him? You may need to cut back on that and give him more hay instead. Alfalfa may be part of the problem too, I don't know though. Oxbow has a great timothy pellet diet that I feed my bunny. My bun gets about 1/2 cup pellets a day along with free feed timothy hay. Mine also gets a cranberry tablet and a papaya tablet everyday.