Total phosphorus analysis was performed on 20 samples of corn distillers dried grains with solubles (DDGS), and three experiments were conducted to determine the bioavailability of P in different samples of DDGS varying in Lys digestibility and heat processing (autoclaving). Relative bioavailability of P was estimated from tibia ash using the slope ratio method after chicks were fed a P-deficient corn-soybean meal diet supplemented with 0.05 or 0.10% P from KH2PO4 or supplemented with 2 levels of the test DDGS (7 to 25%). The mean total P value for the 20 DDGS samples was 0.73 +/- 0.04% (SD), with an average dry matter value of 88 +/- 0.8% (SD). In experiment 1, the bioavailability coefficient for P in a random sample of DDGS relative to KH2PO4 was 69%. In experiment 2, the relative bioavailabilities of P in low digestible Lys DDGS 1, low digestible Lys DDGS 2, and high digestible Lys DDGS 3 were 102, 82 and 75%, respectively (P < 0.05). For experiment 3, the P bioavailability coefficients for a light-colored nonautoclaved DDGS and the same DDGS autoclaved at 121 degrees C and 124 pKa were 75 and 87%, respectively (P < 0.05). Our results showed that the total P content of DDGS was similar to the 0.72% value reported by the NRC (1994), but the relative P bioavailability is higher than the value estimated from NRC (1994) based on table values for total and nonphytate P content. Our results also indicated that there is substantial variability in P bioavailability among different DDGS samples and suggest that increased heat processing may increase the bioavailability of P in DDGS.
There is currently much ongoing research and interest for developing new processing technologies to produce corn distillers dried grains with solubles (DDGS). The current study evaluated a high protein (HP) distillers dried grains (DDG) and a dehydrated corn germ, which are products that can be produced by a modified dry milling process. Two chick experiments were conducted to determine the P bioavailability based on tibia ash. In addition, precision-fed rooster assays were conducted to determine TME(n) and amino acid digestibility. In the first chick assay, a P-deficient cornstarch-dextrose-soybean meal basal diet containing 0.10 to 0.13% nonphytate P was supplemented with 0.0, 0.05, and 0.10% P from KH(2)PO(4) or 7 and 14% conventional DDGS, HP DDG, and corn germ. In the second experiment, the P-deficient basal was supplemented with 7 and 14% conventional DDGS and 12.5 and 25% HP DDG. New Hampshire x Columbian female chicks were fed the experimental diets from 9 to 22 d posthatch, and bioavailability of P was estimated using the slope-ratio method where tibia ash was regressed on P intake. The total P content (90% DM basis) of the conventional DDGS, HP DDG, and corn germ were 0.76, 0.33, and 1.29%, respectively. Bioavailabilities of the P in conventional DDGS, HP DDG, and corn germ relative to KH(2)PO(4) were found to be 60, 56, and 25%, respectively. The TME(n) in conventional roosters was found to be significantly reduced for HP DDG and increased for the corn germ when compared with the conventional DDGS. The protein content (90% DM basis) of the HP DDG and corn germ was 33 and 14%, respectively, and the total lysine as a % of CP was approximately 2 times greater for the corn germ than for the HP DDG. Amino acid digestibilities in cecectomized roosters were consistently higher for the corn germ than for the HP DDG, which was similar to conventional DDGS.
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 KH(2)PO(4) 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 KH(2)PO(4) 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 degrees C for 60 to 80 min or by heating in a drying oven at 121 degrees 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 microm. 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.
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