Help is my baby bunny sick?

I recently got a baby black and white mini rex. His name is Pongo. When i got him he had diarrhea really bad. I don't think the owner took care of him very well. Anyway, I got him on a regular diet of pellets. He has the normal rabbit poops but along with them there are like long turds similar to cat poop. Ive never seen this in rabbits before. Anyone know why he is doing this?