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.

For the first experiment, a total of 32 weanling barrows were fed four diets. The  basal diet consisted mainly of corn, soybean meal, and fish meal. The three experimental diets were formulated by mixing 70% of the basal diet with 30% whey powder, whey permeate, or low-ash whey permeate.

The concentrations of both digestible and metabolizable energy in whey permeate were less (P < 0.01) than in whey powder and in low-ash whey permeate, on both an as-fed basis and a dry matter basis (Table 1). This is partly due to the reduced gross energy concentration in whey permeate compared with the other two ingredients. Protein is removed from whey powder to produce whey permeate, resulting in a greater concentration of lactose and ash. Because ash does not contribute energy to the diet, the energy concentration is decreased. When the ash is removed from whey permeate to create low-ash whey permeate, the gross energy concentration is increased. The digestible and metabolizable energy content did not differ between whey powder and low-ash whey permeate.

In the second experiment, a total of 32 weanling barrows were fed four diets. Three diets consisted of cornstarch, sugar, and 30% whey powder, whey permeate, or low-ash whey permeate. The whey products were the only sources of phosphorus in the experimental diets. The last diet was a phosphorus-free diet, which was fed to estimate the basal endogenous loss of phosphorus.

The concentrations of phosphorus in whey powder and whey permeate did not differ, and both were much greater than in low-ash whey permeate (Table 2). The apparent total tract digestibility of phosphorus was much less  in low-ash whey permeate compared with that of whey powder and whey permeate. However, when values for he apparent total tract digestibility of phosphorus were corrected for the endogenous losses of P,values for the standardized total tract digestibility of P were calculated. These values were not different among ingredients and the standardized total tract digestibility of phosphorus was excellent ( > 91% ) in all three ingredients.

• Whey powder and low-ash whey permeate do not differ in their concentrations of digestible and metabolizable energy. Whey permeate has less digestible and metabolizable energy than the other whey products.
• Apparent total tract digestibility is substantially less in low-ash whey permeate than in whey powder or whey permeate, but there is no difference  among the three ingredients in values for standardized total tract digestibility of phosphorus.
• Phosphorus from all three ingredients is well digested by weanling pigs.

Table 1. Energy values for whey powder, whey permeate, and low-ash whey permeate fed to weanling pigs

^a,b Within a row, values without a common superscript differ (P < 0.05).

Table 2. Digestibility of phosphorus in whey powder, whey permeate, and low-ash whey permeate by weanling pigs

^a,b Within a row, values without a common superscript differ (P < 0.05).

This report is based on research by B.G. Kim, J.W. Lee, and H.H. Stein.