In vitro prediction of phosphorus availability in feed ingredients for swine

The percentage of phosphorus (P) dialyzability was determined in 10 plant-origin and 4 animal-origin feed ingredients using an in vitro procedure that simulates the digestive system of growing swine. The test feed ingredients included alfalfa meal, barley, canola meal, corn, grain sorghum, oats, rice bran, soybean meal, wheat, wheat bran, menhaden fish meal, meat and bone meal, spray-dried blood meal, and dry whey. Repeatability of the in vitro procedure was tested for each ingredient using quadruplicate samples. The in vitro P dialyzability percentages were correlated with published in vivo P availability values for swine. Results showed that P dialyzability with the in vitro procedure was highly repeatable (>96%). For the 10 plant-origin feed ingredients, significant correlations (r =; 0.72-0.88) were found among the in vitro P dialyzability percentages and the published in vivo P availability values. For the four animal feed ingredients, however, the in vitro dialyzability percentages obtained were poorly correlated (r = -0.26 to 0.70, p > 0.3-0.7) with published in vivo P availability values. In conclusion, the in vitro P dialyzability procedure presented here is a valid alternative to conducting in vivo studies far ranking plant-origin feed ingredients in P availability. Fine grinding of the ingredients and the addition of acid phosphatase increased the validity of this in vitro procedure.