Sweet potatoes and butternut squash are also high in fiber if they need it. I seriously doubt you will ever know if they are getting the fiber they "need" or even it it matters in a dog. As long as their stools are not too hard to where they have a difficult time with them, or the stools are too soft, which has no shape to them, just a "patty", then I'm sure they are doing well with what you feed. Of course it doesn't hurt to feed them a little sweet potato or butternut squash once in awhile either.
