In my opinion, current NRC requirements are marginal and tend to promote a short, fat heifer. If heifers grow this way, they will not produce up to their full genetic potential. Research world wide shows that heifer's that get too fat prior to puberty will produce less milk. The fat cells will permanently replace future milk producing cells. This process is not reversible as the animal grows older.
Energy tends to make animals put on weight, while protein tends to promote height.
Most rations are high in energy and low in protein which is the worst combination possible. Rations should be balanced with the proper amount of energy and protein so the heifer grows properly. The correct energy, mineral, and vitamin levels can be found by consulting NRC's Nutrient Requirements of Dairy Cattle. Protein is frequently the key limiting nutrient. By-pass protein must be carefully evaluated in heifer rations.