Phosphorus retention in corn, spray dried plasma protein, soybean meal, meat and bone meal, and canola meal using a precision-fed rooster assay.

Four experiments were conducted to evaluate the precision-fed rooster assay for determining excreta phosphorus retention values for 5 feed ingredients in which roosters were precision-fed the ingredients and excreta were collected quantitatively for 48 h. The first rooster assay determined the effects of increasing P intakes on excreta P retention values for corn. This assay involved feeding either 20 g of corn or 20 g of corn supplemented with increasing amounts of KH2PO4 to provide total P intakes of 51 to 351 mg and non-phytate P intakes of 16 to 316 mg. The excreta P retention value for corn fed alone was 75% but decreased greatly when non-phytate P intakes were 76 mg or higher for the corn diets containing added KH2PO4. The second precision-fed rooster assay involved feeding increasing amounts of spray dried plasma protein (SDPP) (5 to 20 g) which provided non-phytate P intakes of 61 to 242 mg. Excretion of P increased and excreta P retention values decreased from 94 to 60% as SDPP intake increased from 5 to 20 g. Experiment 3 determined excreta P retention values for solvent extracted dehulled soybean meal (SBM) (24 g intake) and also the effect of increasing intakes of SDPP (5 to 10 g) and meat and bone meal (MBM) (1.5 to 10 g) on their excreta P retention values. The excreta P retention value for SBM was 41%. Excreta P retention values for SDPP again decreased as P intake increased. Excreta P retention values for MBM were low (27 to 35%) at all intakes. In Experiment 4, roosters were tube-fed 8, 16, or 24 g of canola meal and excreta P retention values varied from 23 to 35% among intake levels. The results of this study indicated that excreta P retention values often varied greatly among different levels of ingredient and non-phytate phosphorus intake and suggest that the precision-fed assay may be useful for determining bioavailability of P only if non-phytate P intakes are low. In addition, the assay may not be accurate for ingredients which contain high Ca levels such as MBM.

Phosphorus bioavailability in increased-protein, reduced-fiber canola meal, conventional canola meal, and soybean meal fed to crossbred chicks.

Three experiments were conducted to evaluate 3 increased-protein, reduced-fiber canola meals (CM) (CMA, CMB, and Test CM), 2 conventional CM (CCM), and 2 soybean meals (SBM). For determination of P bioavailability in CM and SBM, a P-deficient cornstarch-dextrose-SBM basal diet was fed as Diet 1. The latter basal diet was then supplemented with 0.05 and 0.10% P from KH2PO4 or 12.5 and 25% of a CM or SBM. In addition, the effect of phytase enzyme on bioavailability of the P in CMA, Test CM, and one of the CCM was determined using P-deficient 45% CM-cornstarch-dextrose diets (0.11 to 0.15% non-phytate P), with a CM as the only source of dietary P. Additional diets contained 0.05 and 0.10% added P from KH2PO4 or 125 to 500 units phytase added per kg of diet. Crossbred chicks (New Hampshire X Columbian) were fed the experimental diets from 8 to 21 d post hatch in all experiments, and bioavailability of P was estimated using the slope ratio method in which tibia ash was regressed on supplemental P intake. A linear increase in tibia ash was observed as the P level increased by the addition of KH2PO4, CMA, CMB, or SBM. Based on the mean values of tibia ash in mg/tibia and tibia ash %, the mean bioavailabilities of P in the 3 increased-protein, reduced-fiber CM, 3 CCM, and 2 SBM relative to KH2PO4 were 18, 15, and 39%, respectively. A linear increase in weight gain and tibia ash was observed with addition of KH2PO4 or phytase to the P-deficient CM diets. It was estimated that 125 or 250 units/kg microbial phytase resulted in approximately 0.05 and 0.10% P being released from CM, respectively. In conclusion, the bioavailablity of the P in the new increased-protein, reduced-fiber CM was similar to that of CCM. Furthermore, phytase substantially and similarly increased the bioavailability of P in both types of CM.