If he's not cleaning himself, that's aproblem. You should take him to a vet to see if it's morethan just dietary. He might be having mobility problems, orhe could be too obese to be able to reach his rear endcomfortably. Unfortunately that's not uncommon withpets. Sometimes the only cause is dietary and the bun simplycan't clean up the gross poop he's getting from food that doesn't agreewith him. But it's always best to have a vet check.
What are you feeding him? It's a good idea to cut out any andall treats and fruits, especially if he has treats in hispellets. Like Kaytee Fiesta. Never feed any pelletthat has treats mixed in. All those carbs tend to overloadthe bun's system, resulting in unusually squishy (sometimes liquid)smelly cecals (they type of poop they're supposed to eat forvitamins). If you're feeding him veggies, think back and seeif there's anything new that was added just before he started havingmessy butt problems. It might be a good idea to stop feedinghim all veggies for a while, then slowly start reintroducing them oneat a time so you'll know which ones are problems for him.
Also, some rabbits don't tolerate alfalfa pellets very well.Even if they were fine with them when they were babies, as adults theysometimes need a pellet that's less rich. If you're feedingalfalfa pellets, try switching to a timothy pellet like Oxbow BB/T orKaytee Timothy Complete.
Also, make sure that he always has access to grass hay such as timothy, orchard grass, or oat hay.
This thread in the Rabbit Health References has more info:
http://rabbitsonline.net/view_topic.php?id=11935&forum_id=10
