Bioavailability of phosphorus from various phosphates based on body weight and toe ash measurements

Two experiments involving 1,152 turkeys were conducted to determine the relative bioavailability of phosphorus of eight phosphates from commercial and experimental sources. The basal diet, composed of 52% dehulled soybean meal and 41% ground yellow corn, contained 1.48% calcium and .44% total phosphorus. Phosphorus from the eight sources was added to the basal diet at levels of .09, .18, or .27% to form 24 diets with a constant calcium content. Each diet was fed to one pen of eight males and eight females from 1 to 4 wk of age in the first experiment and to two pens (one of each sex) of 16 poults/pen from 0 to 4 wk of age in the second experiment. Measurements of percentage ash of the middle toe pooled from all poults within a pen and of average body weight at 4 wk of age provided similar relative phosphorus availability values. With the phosphorus in monocalcium phosphate as the standard set at 100%, phosphorus from two sources of dicalcium phosphate and one source of defluorinated phosphate were found not significantly different in bioavailability (95, 105, and 103%, respectively). Phosphorus in curacao phosphate was only 55% available and in the three experimental defluorinated phosphates, phosphorus was 81, 70, and 87% available. Significant differences in bioavailability between two samples greater than 13 and 18% were found when using toe ash and body weight measurement, respectively.