We have been stressing the desirability of having first calf heifers calve at less than 26 months of age. Some dairymen have been resistant to this because they felt that young heifers did not do well during their first lactation relative to older heifers. This is weight after the calf is born. Heifers that reach this size generally do well and have the ability to peak at 70 or more lbs. of milk per day. Table 1 contains requirements for three ages of heifers.
Younger heifers consume less feed, so the nutrient density needs to be higher.
Virginia Tech research suggests that energy content of diets for a given rate of gain should be adjusted according to housing and environmental conditions. Adjust pounds of grain fed per day based on observed gain. Notice that calcium and phosphorus concentration declines as the heifer gets older, but the other minerals do not change with age. Part of this is due to a lack of information about the requirements for some of these nutrients, especially the microminerals. This would be true for all of the other nutrients if actual quantity was expressed instead of concentration.