Whey powder is a co-product of the cheese industry, and consists primarily of lactose and protein. The inclusion of whey powder in weanling pig diets improve growth performance; this is believed to be due to the lactose fraction. Because of the demand for whey protein from the human food industry, the protein is sometimes extracted from whey powder. The resulting product is called whey permeate.

Few values for digestible and metabolizable energy in whey permeate have been reported. In addition, the standardized total tract digestibility (STTD) of phosphorus in these ingredients has not been reported. Therefore, two experiments were conducted: the first, to determine the concentrations of digestible and metabolizable energy in whey powder, whey permeate, and low-ash whey permeate; and the second, to determine the apparent and standardized total tract digestibility of phosphorus in the same ingredients.