Well, if you do one, I would recommend Rice Bran, it does help a bit more, although a bit more expensive, you will have to feed a lot of the beet pulp if you are only using beet pulp. Once he gains weight, and is at a healthy weight, I would feed beet pulp, it is one of the cheapest grains, and helps a lot maintaining a healthy weight.
I feed rice bran in summer, only a handful to get her to eat her selenium supplement, and beet pulp and rice bran in summer, she is a hard keeper in winter but a way easy keeper in summer, although she is worked hard in summer and lightly in winter. I feed beet pulp just to help maintain weight a bit more, due to the fiber, and to keep her warm, also due to fiber.
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown