Biological values of phosphorus from various sources for young turkeys.

Two experiments, each utilizing 540 turkeys, were conducted to determine the biological value of phosphorus from 13 different sources when compared with that from dicalcium phosphate (dihydrate, purified) as a standard. Each phosphorus source was added to a basal diet composed of 44% ground yellow corn and 52% dehulled soybean meal to supply .09, .18, .27, or .45% inorganic phosphorus. Each of 60 diets, which included duplicates of the standard source, was fed to a pen of 9 male poults from 1 day to 3 weeks of age in each experiment. Body weight and toe ash measurements of poults collected at 3 weeks of age were used in nonlinear (exponential) bioassays to obtain relative biological values of phosphorus from various sources. With the dicalcium phosphate standard set at 100%, the average relative biological values of three samples from each of commercial monocalcium phosphate (21% P), dicalcium phosphate (18.5% P), and defluorinated phosphate were 93, 81, and 70%, respectively. Four samples of experimental defluorinated phosphate averaged 75%. Differences of about 5% between values were required for statistical significance, indicating significant differences among these biological values of phosphorus from the various phosphate sources in diets of young turkeys.

Bioavailability of phosphorus in various phosphate sources using body weight and toe ash as response criteria.

The relative bioavailability values of P from seven sources were determined using male chickens fed a basal corn-soybean meal diet (.40% total P and 1.10% Ca) with varying levels of test and standard phosphates from 0 to 3 wk of age. Each of seven test phosphates was added to the basal diet at .05, .08, .12, .17, .23, and .32% levels. In addition, standard diets were formulated by adding the same levels of P plus .44 and .60% levels from dicalcium phosphate dihydrate (CaHPO4.2H2O) to the same basal diet. Each of the 42 test diets was fed to two pens of 10 chicks each, and each of the standard diets was fed to six pens of 10 chicks each. Three-week body weight gain and percentage ash of dried toe data were fitted with nonlinear (asymptotic and sigmoidal) regression equations, and the ratios of regression coefficients were used to determine the bioavailability of various test phosphates relative to the reference standard. Based on the asymptotic regression equation of body weight gain and on the sigmoidal regression equation of toe ash on the percentage of P added to the diets from the seven phosphate sources, the average relative bioavailability of the P (compared with the standard given a value of 100%) was as follows: Lucaphos-48, 88.4%; Lucaphos-40, 95.1%; Rukana, 83.7%; Cefkaphos-N, 104.8%; phosphoric acid, 93.0%; monocalcium phosphate monohydrate [Ca(H2PO4)2.H2O], 111.8%; and Biophos, 92.0%. A difference of 7.7% units for the average bioavailability of the P was required for significance (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of various response criteria in assessing biological availability of phosphorus for broilers.

The relative bioavailability of P from seven sources was determined in relation to a standard dicalcium phosphate dihydrate (CaHPO4.2H2O) in a 21-d assay involving 1,320 broiler male chicks using several response criteria. The seven sources (Lucaphos-48, Lucaphos-40, Rukana, Cefkaphos-N, phosphoric acid, monocalcium phosphate monohydrate, or Biophos) were added to the basal diet (.40% total P and 1.10% Ca) at levels to supply .05, .08, .12, .17, .23, and .32% P. Two additional levels (.44 and .66%) of P from dicalcium phosphate dihydrate were included for the standards. The criteria selected to evaluate included tibia ash, tibia specific gravity, tibia shear force, toe shear force, and metatarsal shear force. Other criteria: weight, length, diameter, and volume of tibia; weight, volume, and specific gravity of metatarsus; and weight, volume, and specific gravity of toe were not selected because their response to increasing P levels were inconsistent and quite variable. Nonlinear (asymptotic and sigmoidal) regression equations were fitted to the data than linear equations. The ratios of regression coefficients were used to determine the bioavailability of various test phosphates relative to the reference standard. The results indicated that the response criteria used for the determination will considerably influence the relative bioavailability estimates of a P source. Body weight gain and toe ash percentage were found to be an equally or a more sensitive criteria for assessment of P availability than tibia ash. Tibia specific gravity, tibia shear force, toe shear force, and metatarsal shear force were of limited value as response criteria in P bioavailability assays based on standard error and difference required for significance.