Assessment of the quantity of biologically available phosphorus in yeast RNA and single-cell protein

Two assays were conducted with chicks fed a phosphorus-deficient crystalline amino acid diet from day 8 to 17 posthatching to evaluate the phosphorus availability of purified torula yeast RNA and single-cell protein (Torula yeast). Tibia bone ash of the chicks was the criterion used in both assays, and regression analysis was used to evaluate bone ash as a function of phosphorus intake. A standard curve was established by feeding graded levels of KH2PO4 in each assay. Weight gain, tibia weight and tibia ash all responded to phosphorus supplementation whether provided by KH2PO4, RNA or single-cell protein. Weight of tibia ash provided the best linear fit when evaluated as a function of phosphorus intake. Availability in both assays estimated using the slope-ratio technique wherein milligrams of available phosphorus per gram of RNA or single-cell protein was calculated. In assay 1 the available phosphorus in RNA was found to be 93.2 mg/. In assay 2 the available phorphorus in single-cell protein was found to be 14.1 mg./g.