You don't mention your location, quality or quantity of grass, plans for these heifers, or how much of the calf finisher and cubes your feeding but, if you're planning on breeding them, I don't believe I would be feeding them calf finisher because A) it's probably costing you more money than is necessary, and B) it probably contains more protein than they need, and can also cause them to become too fat to breed. Hay cubes also tend to be fairly high in protien and can cause the same problem, depending on how much you're feeding/sitting, and the quality/quantity of your grass, as well as your weather. I would probably alternate good quality alfalfa with a good quality grass hay, or feed a good quality alfalfa/grass mix - the amount fed would, again, depend on the quality and quantity of your grass. I might also feed a pound - possibly two of corn/animal/day, depending on the quality of hay and grass. I don't mean to be so ambigious, but supplements depend entirely on the quality and quantity of the grass that is available, and on the winter weather. Whatever I decided to feed, I would make sure they didn't get overly fat because that will cause problems with breeding, and will cause you to take a hit if you're planning on selling them.