Judges generally arent going to handle breeding animals, and finish isnt really important in breeding animals. We want them healthy and in good flesh. You definately want the heifer in great body condition going into breeding season. Not only will this increase her chances of settling, but it will also make her look better after calving. If one is behind when bred, it is hard to get both cow and calf in good condition and looking good when she calves. But by all means do not try to increase fat just before calving. Not only to fatter cows generally have more calving difficulty, the fetus grows exponentially during that last trimester. By increasing the engergy in the cows diet to get her fat you also increase the energy the calf is receiving and make that calf grow even more, greatly increasing the chance that you are gonna have a huge calf you have to pull. You dont want this in any cow, but especially not in a first calf heifer!