You always have to be careful adding fat to a diet. To much fat can be trouble in many ways. Fat in the diet can actually be an appetite limiter, meaning the higher percent of the ration that is fat, the less the animal will want to eat. As someone already mentioned, we dont know the staage your heifer is at. But if you get to much fat on the heifer to young you can actually stunt skeletal growth and if she is to fat around the time your trying to breed her you can greatly decrease conception rates. Also heifers that get to fat will often deposit fat in the udder which can greatly reduce milk production when she is trying to raise that calf.
About 3% fat in the ration is generally very adequate for a heifer, and I typically try to avoid going over 5% in my rations. SBM isnt really the best fat source because the fats generally come in the oils and we loose some of those when we grind grains into meals. SBM however is an amazing protein source which is generally more important to the diets of growing calves. True that we want a littly cover on the heifers to show, but if you provide the necessary protein to develop muscle she will naturally look "fatter" without having the risk of putting on to much actual fat.
If I have a heifer that just really needs more fat before a show, I try not to start adding the extra fat to the diet until about 30 days before the show. This should be adequate time for her to put on some cover before the show. If I have a couple months between shows, I try to back someof the fat out of the diet between shows and increase the protein to get more muscle and skeletal growth.
