Effect of increased heat processing and particle size on phosphorus bioavailability in corn distillers dried grains with solubles

Previous studies have reported that increased heat processing and feeding larger particle size ingredients may increase the bioavailability of phytate P in some feedstuffs. Therefore, one chick experiment was conducted to determine the effect of various increased heat processing treatments on bioavailability of P in corn distillers dried grains with solubles (DDGS), and 2 chick experiments were conducted to determine the effect of particle size on bioavailability of P in DDGS. In addition, one precision-fed cecectomized rooster assay was conducted to evaluate the effects of increased heating on amino acid digestibility. For the chick experiments, a P-deficient cornstarch-dextrose- soybean meal basal diet containing 0.10% nonphytate P was supplemented with 0.0, 0.05, or 0.10% P from KH₂PO₄ or 1 of 2 levels of DDGS. Diets were fed from 8 to 22 d of age, and P bioavailability relative to the P in KH₂PO₄ was estimated using the standard curve or slope-ratio methods with tibia ash as the response variable. Increased heating of DDGS by autoclaving at 124 kPa and 121°C for 60 to 80 min or by heating in a drying oven at 121°C for 60 min significantly increased relative P bioavailability in DDGS (from 70 to as high as 91%) in several treatments. Amino acid digestibility, however, was greatly reduced by increased heating in most cases, particularly for Lys. Relative bioavailability of P was not significantly affected by DDGS particle sizes ranging from 542 to 837 μm. Our results indicated that increased heating of DDGS increased bioavailability of P but decreased digestibility of amino acids, particularly Lys, and that bioavailability of P was not affected by particle size.