The Relation of Dietary Particle Size to Phosphorus Availability in Purified Diets

SINCE most natural feedstuffs contain some phosphorus, purified diets are frequently used in assaying phosphates to determine the relative availability of the phosphorus they contain. However, when some phosphates were fed to chicks or poults in purified diets, bone ash of the experimental animal was not as high as when the same level of phosphate was fed in diets made up of practical ingredients (Scott et al., 1962; Carlson et al., 1964; Griffith et al., 1966). These results caused the postulation of an anti-rachitic factor in the practical ingredients, but Griffith (1968a, b) found that grinding practical ingredients to a powder destroyed the “anti-rachitic” factor and concluded that the anti-rachitic effect of soybean meal and hulls was due to size of the particles making up the diet rather than to a chemical compound. Further work supporting this view was reported by Griffith (1969). The experiments reported below were undertaken to…