I can't quite tell from this pic, but is there a protrusion that is mainly on the right side there? Or, is it all the way around? A little "puffiness" is normal, but if there is a larger lump or area, then a vet should probably look at it - it could be just that the anal glands are full. What are you feeding? If it is the glands, you may want to change to a different diet as this can help avoid the filling, and allow for the normal, natural emptying that occurs when the poo.
