Vitamin A can be useful on a year-round basis and may be carried in the mineral. This will be dictated by source and quality of forage. Mature or weathered grass or hay require addition of protein and energy supplements to maintain active growth rates. High quality grass-legume forages will not require protein supplementation if provided in sufficient quantity. Protein source must also be considered.
Many commercial supplements contain at least some urea in addition to the natural proteins.
For best results with young, growing heifers, no more than one-third of the supplemental protein should be from a chemical source such as urea. Pasture is an important source of feed for the heifer. If adequate growth was made during the wintering period, good pasture will provide sufficient growth through breeding and supplementation will not be necessary during grazing. The desired rate of gain during the second wintering period again will depend on the heifers' condition, weight and breed. Lightweight, thin heifers need to gain more than heavy, fatter heifers.