The primary difference in nutrient content of a 20, 32, or 40 percent protein supplement is the protein concentration, not energy. Thus, supplements are often categorized as protein or energy supplements based on the protein content alone. Developing a cost-effective supplementation program is typically dependent on identifying the most limiting nutrient and providing the limiting nutrient(s) at the lowest cost. If protein is deficient (i.e., < 7 percent crude protein) and forage supply is adequate, supplements should be evaluated based on $/lb protein because animal response will be to protein (calculation: cost/ton ÷ (% protein/100) * 2000 lb = $/lb protein). Studies have compared high and low protein supplements delivered to provide the same amount of protein to cows and heifers when forage is not limited, and results show that performance is equal. That is, the performance achieved by feeding 4 lb/d of a 20 percent protein supplement is equal to the performance achieved by feeding only 2 lb/d of a 40 percent protein supplement when there is enough grass. Even though the high protein supplement costs more per ton, because it is fed at half the amount of the 20 percent supplement, it costs less per day. So, if forage supply is adequate, a higher protein supplement is likely most cost effective. If additional energy is needed, a lower protein supplement fed at a much higher amount is likely a better option.