Biological value of bone-precipitated dicalcium phosphate in turkey starter diets

A study was conducted to determine the relative biological value (RBV) of phosphorus from two bone-precipitated dicalcium phosphates (DCP-BP) in turkey starter diets. An estimated 40,000 metric tons of DCP-BP are produced annually in the United States as a by-product of gelatin production. The two DCP-BP sources were compared to commercial feed phosphates. Two bioassay experiments of 21-d duration were conducted with female turkeys. Phosphate sources were each fed at three levels (.18, .24, and .36% added total phosphorus) in a corn-soybean meal diet. Calcium level was maintained constant at 1.0% in all diets by adjusting the level of ground limestone. Four replicate pens of six poults were randomly assigned at 1 d of age to each level of each phosphorus source in each bioassay. The reference standard was United States Pharmacopeia (USP) grade calcium phosphate, dibasic dihydrate. Data representing three response criteria (weight gain, gain:feed ratio, and tibia ash percentage at 21 d) were combined to calculate a biological value (BV) for each test source and the reference standard phosphate. A RBV was then computed for each test source. The RBV of the two DCP-BP sources were 98.8 and 99.1, as compared to 100.0 for the reference standard, and 86.7, 87.1, and 88.4 for three commercial, thermochemically produced defluorinated phosphates. The RBV of one commercial mono-dicalcium phosphate, and three di-monocalcium phosphates were: 96.4, and 91.2, 94.7, and 101.5, respectively. The two DCP-BP sources compared favorably to commercial feed phosphates, and would be satisfactory supplements in diets for starting chicks, poults, pigs, and other species.