Two experiments were conducted to examine the relative precision of bone densitometry and bone ash methodologies as response criteria in measurement of bioavailability of phosphorus from various supplements for turkeys. Multivariate analyses of variance were used to analyze data collected. Coefficients of correlation and variation and F ratios were used for evaluation. Bone densitometry with one scan at each of 3 points on the bone was faster than bone ash and as precise as bone ash analysis in measuring phosphorus availability in turkeys. The coefficient of correlation between percentage ash (of dry bone) and scan density (milligrams per centimeter length of bone) measurements for treatment effects was .986. The coefficient of variation was about the same for the bone ash (5.8) and the three-point bone scan (6.9) methods. As indicated by the F ratio for testing treatment effects, bone densitometry was better able to detect differences among phosphorus sources. A technician may scan 50 cleaned bones in 3 hr, but with the bone ash method, drying, ashing, and weighing may require 3 working days. Bone sampling technique, multiple operators, different bone sizes, and decay of iodine source were the major factors affecting precision of the bone densitometry technique. Relative biological availabilities of phosphorus from various supplements were about the same by the two methods.

Four samples of turkey litter ash residue (produced in fluidized-bed reactor) have been evaluated for phosphorus bioavailability utilizing a turkey growth assay with bone ash as the response criterion. Availabilities obtained were 80.6, 87.5, 77.6, and 72.4% in comparison to availability from calcium phosphate monobasic monohydrate at 100. Although the values with the litter ash supplements were significantly (P<.05) lower than the standard, this material shows promise as a source of phosphorus in poultry nutrition. (