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

Abstract

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 48h. The first rooster assay determined the effects of increasing P intakes on excreta P retention values for corn. This assay involved feeding either 20g of corn or 20g of corn supplemented with increasing amounts of KH2PO4 to provide total P intakes of 51 to 351mg and non-phytate P intakes of 16 to 316mg. The excreta P retention value for corn fed alone was 75% but decreased greatly when non-phytate P intakes were 76mg 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 20g) which provided non-phytate P intakes of 61 to 242mg. Excretion of P increased and excreta P retention values decreased from 94 to 60% as SDPP intake increased from 5 to 20g. Experiment 3 determined excreta P retention values for solvent extracted dehulled soybean meal (SBM) (24g intake) and also the effect of increasing intakes of SDPP (5 to 10g) and meat and bone meal (MBM) (1.5 to 10g) 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 24g 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.