Phosphorus Bioavailability, True Metabolizable Energy, and Amino Acid Digestibilities of High Protein Corn Distillers Dried Grains and Dehydrated Corn Germ E. J. Kim, C. Martinez Amezcua, P. L. Utterback, and C. M. Parsons 1 Department of Animal Sciences, University of Illinois, Urbana 61801 ABSTRACT 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-dextrosesoybean 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 Columbian Key words: high protein distillers dried grains with solubles, corm germ meal, phosphorus, chick INTRODUCTION Corn distillers dried grains with solubles (DDGS) is a coproduct of the ethanol industry and has traditionally been fed primarily to ruminants due to its high fiber content and variability of nutrients (Singh et al., 2005). Poultry diets must be formulated precisely, and research has shown that observed nutrient profiles of recent samples of DDGS vary from earlier reported values (Spiehs et al., 2002; Gibson and Karges, 2006). The DDGS can be a good source of protein, but it has been shown to be highly variable. One major cause of the protein and amino acid variability is that the solid and liquid streams of DDGS production are not highly regulated (Belyea et al., 1998). One amino acid of particular concern is lysine. During the drying process, high temperatures can dam- 2008 Poultry Science Association Inc. Received July 20, 2007. Accepted January 5, 2008. 1 Corresponding author: poultry@uiuc.edu 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. 2008 Poultry Science 87:700 705 doi:10.3382/ps.2007-00302 age proteins and cause a reduction in available amino acids, especially lysine. This is mainly due to the reaction of lysine with carbohydrates, specifically reducing sugars (Cromwell et al., 1993; Spiehs et al., 2002). Previous research has shown that the color of DDGS and lysine digestibility may be correlated, a darker brown color being indicative of the greater occurrence of the Maillard browning reaction and less available lysine (Fastinger et al., 2006). The DDGS can also be a good source of P, but P bioavailability is highly variable. The NRC (1994) for poultry reports that 54% of total P is nonphytate, but research has shown that bioavailability values can vary over a wide range (Singsen et al., 1972; Whitney et al., 1999). Martinez Amezcua et al. (2004) reported P bioavailability values between 69 to 102%, with an average of 82%. Lumpkins and Batal (2005) reported similar estimated bioavailability values of 68 and 54% for 2 samples of DDGS. The bioavailability of P for poultry is important because it is essential for growth and metabolism and is one of the most expensive nutrients in poultry diets. Any P that is not utilized will be excreted and can cause detrimental environmental effects. 700
EVALUATION OF DISTILLERS DRIED GRAINS WITH SOLUBLES 701 Because ethanol production is expected to increase exponentially in the next 5 yr, the production of DDGS will increase proportionately. As ethanol demand increases, the industry is creating new production technologies that will maximize production of ethanol from corn. One approach is to fractionate the corn before processing so that nonfermentable fractions of the corn are removed before fermentation (Singh et al., 2005). Because the corn is fractionated before fermentation, the nutrient profile of DDGS will change and new coproducts or modified DDGS will be produced (Singh et al., 2005). Because the nonfermentable fractions, bran, pericarp fiber, and germ, are removed before fermentation, the modified product will contain higher protein levels and decreased levels of fiber and can be marketed as high protein (HP) DDG without solubles (Gibson and Karges, 2006). Thus, these processing modifications create 2 new products that can be used in poultry feed, namely HP DDG and dehydrated corn germ. It is important to determine the nutritional value of these new products for poultry. The objectives of this study were to determine the bioavailability of P, TME n, and amino acid digestibilities for HP DDG and corn germ in comparison to a conventionally processed (CONV) DDGS. MATERIALS AND METHODS Nutrient Analysis Samples of the HP DDG, dehydrated corn germ, and CONV DDGS were obtained from POET Nutrition, Sioux Falls, ND. The HP DDG and corn germ were produced using modified dry grind technologies similar to those described by Singh et al. (2005). The HP DDG and corn germ were produced in the same modified ethanol plant, whereas the CONV DDGS was produced at a separate facility that utilized the same equipment for ethanol production except for the specialized equipment to fractionate the corn kernel before fermentation. The samples were analyzed for DM (930.15), crude fat (920.39), CP (990.03), and total P (965.17 and modified 985.01) using the AOAC International (2000) procedures. Chick Experiments for P Bioavailability Two chick experiments were conducted with chicks to determine P bioavailability. All animal housing, handling, and euthanasia were approved by the University of Illinois Animal Care and Use Committee. New Hampshire Columbian females were used in both experiments. The chicks were housed in thermostatically controlled starter battery cages with raised wire floors in an environmentally controlled room with light provided continuously. From d 1 to 9 posthatching, chicks received a nutritionally complete corn and soybean meal-based starter diet (NRC, 1994) containing 23% CP and 3,100 kcal of ME/kg. On d 9 after hatching, following an overnight period of feed removal, chicks were weighed, wingbanded, and assigned to treatment groups so that their Table 1. Composition of the phosphorus deficient basal diet 1 Amount Ingredient (%) Cornstarch/dextrose (2:1 ratio) to 100 Soybean meal 47.37 Soybean oil 5.00 Limestone 1.63 NaCl 0.40 Vitamin mix 2 0.20 Mineral mix 3 0.15 Choline chloride 60% 0.10 DL-Met 0.25 Bacitracin-MD premix 4 0.040 1 Calculated to contain 23% CP, 3,300 kcal/kg of TME n, 0.10% nonphytate P, 0.75% Ca, 1.4% lysine, and 0.91% methionine + cystine. 2 Provided per kilogram of diet: retinyl acetate, 4,400 IU; cholecalciferol, 25 g; DL- -tocopheryl acetate, 11 IU; vitamin B 12, 0.01 mg; riboflavin 4.41 mg; D-pantothenic acid, 10 mg; niacin, 22 mg; menadione sodium bisulfite, 2.33 mg. 3 Provided as milligrams per kilogram of diet: manganese, 75 from MnSO 4 H 2 O; iron, 75 from FeSO 4 H 2 O; zinc, 75 from ZnO; copper, 5 from CuSO 4 5H 2 O; iodine, 0.75 from ethylene diamine dihydroiodide; selenium, 0.1 from Na 2 SeO 3. 4 Contributed 13.75 mg/kg of bacitracin methylene disalicylate (5.5%). initial weights were similar among treatment groups. Four replicate groups of 5 chicks were fed experimental diets from 9 to 22 d of age. Feed and water were provided for ad libitum consumption. At the end of the experiment, all chicks were euthanized with CO 2 gas and the right tibia bone was collected, autoclaved, cleaned, dried at 105 C, weighed, and dry-ashed at 600 C to determine bone ash. Experiment 1 consisted of 9 treatments. Diet 1 was a P-deficient basal diet that provided a calculated 0.1% nonphytate P (Table 1). Diets 2 and 3 were the same as the basal diet plus an additional 0.05 and 0.10% of P from KH 2 PO 4, respectively. Diets 4 and 5, 6 and 7, and 8 and 9 were the basal diet that was supplemented with 7 and 14% of the CONV DDGS, HP DDG, and corn germ, respectively. The ingredient supplementations to the basal diet were in place of cornstarch and dextrose. Body weight gain, feed consumption, feed efficiency, and tibia bone ash in milligrams per tibia and as a percentage were measured. A second chick P bioavailability assay was conducted to confirm the results of P bioavailability of HP DDG from the previous chick assay. The second experiment consisted of 7 treatments. Diet 1 was the same P-deficient basal diet used in experiment 1 except that it was supplemented with a small amount of KH 2 PO 4 to provide a calculated 0.128% nonphytate P. Diets 2 and 3 were the basal diet plus an additional 0.05 and 0.10% of P from KH 2 PO 4, respectively. Diets 4 and 5 were the basal diet supplemented with 7 and 14% of the CONV DDGS. Diets 6 and 7 were the basal diet supplemented with 12.5 and 25% of the HP DDG. The higher levels of HP DDG compared with experiment 1 were used in attempt to produce a larger tibia ash response from this ingredient. The ingredient supplementations to the basal diet were in place of cornstarch and dextrose. Body weight gain, feed con-
702 KIM ET AL. Table 2. Dry matter, fat, protein, and TME n contents of conventional distillers dried grains with solubles (DDGS), high protein distillers dried grains (DDG), and dehydrated corn germ 1 Dry matter Fat Protein 2 TME n Sample (%) (%) (%) (kcal/g of DM) Conventional DDGS 91.9 10.0 25.3 3.554 b High protein DDG 91.1 2.9 44.1 2.957 c Corn germ 95.4 19.1 14.9 4.336 a a c Means within a column with no common superscript differ significantly (P < 0.05). 1 All values except TME n are presented on an air-dry basis. Values for dry matter, fat, and protein are means of duplicate analyses. 2 Means for 5 conventional roosters. sumption, feed efficiency, and tibia bone ash in milligrams per tibia and as a percentage were measured. TME n and Amino Acid Digestibility Two precision-fed rooster assays, one with conventional and one with cecectomized Single Comb White Leghorn roosters, were conducted. After 24 h of feed withdrawal, 5 cecectomized roosters and 5 conventional roosters were precision-fed approximately 20 g of CONV DDGS, HP DDG, or corn germ. Excreta were then collected for 48 h. Feed and excreta from conventional roosters were analyzed for N as described previously and for gross energy using an adiabatic bomb calorimeter standardized using benzoic acid and TME n as described by Parsons et al. (1992). Excreta from cecectomized roosters were analyzed for amino acids at the University of Missouri-Columbia experiment Station Chemical Laboratories [method 982.30 E (a, b, c); AOAC International, 2000] and amino acid digestibility coefficients were calculated. Endogenous corrections for energy and amino acids were made by using roosters that had been fasted for 48 h. Statistical Analysis Data from the chick assays were initially analyzed using the ANOVA procedure of SAS (SAS Institute, 1990) for completely randomized designs. Statistical significance of differences among individual treatments was assessed using the least significant difference test (Carmer and Walker, 1985). Data were further analyzed for the P bioavailability using multiple linear regression by regressing the dependent variable of tibia bone ash (mg/ chick) on the independent variables of supplemental P intake (g/chick) from KH 2 PO 4 and the CONV DDGS, HP DDG, and corn germ. Bioavailability of P in the test samples relative to the standard KH 2 PO 4 was then estimated using the slope-ratio method (Finney, 1978). The TME n and amino acid digestibility values were analyzed by ANOVA using the SAS system, and differences among means were assessed using the least significant difference test. RESULTS AND DISCUSSION Nutrient composition of the CONV DDGS, HP DDG, and corn germ are presented in Table 2. The TME n in conventional roosters was found to be significantly increased in the corn germ when compared with the HP DDG and the CONV DDGS. The increased TME n for corn germ can be attributed mainly to the increased crude fat content, which was higher for the corn germ in comparison to the CONV and HP DDG. The CP content was increased from 25% for CONV DDGS to 44% for the HP DDG. The latter increase in protein was due to the removal of the germ and pericarp fiber. The corn germ had a lower CP of 15% when compared with the 2 DDGS samples. This difference was expected because the germ contains a lower concentration of protein and a higher concentration of fat than the endosperm (Shukla and Cheryan, 2001). Table 3. Growth performance from 9 to 22 d tibia ash for chicks in first P bioavailability assay, experiment 1 1 Tibia ash Dietary Weight Feed Gain:feed treatment gain (g) intake (g) (g/kg) (mg/tibia) 2 (%) 1. Basal diet (B) 285 d 444 d 640 323 f 33.3 e 2. B + 0.05% P 3 306 c 474 c 645 408 c 36.9 b 3. B + 0.10% P 3 322 ab 503 ab 640 495 a 41.2 a 4.B+7%DDGS-CONV 4 306 c 481 bc 637 367 e 34.9 de 5. B + 14% DDGS-CONV 4 328 a 511 a 640 443 b 38.3 b 6.B+7%HPDDG 4 286 d 438 d 654 327 f 33.7 e 7. B + 14% HP DDG 4 313 bc 487 abc 643 370 de 34.9 de 8.B+7%corn germ 306 c 473 c 647 365 e 34.7 de 9. B + 14% corn germ 314 abc 500 abc 631 394 cd 35.7 cd Pooled SEM 5 10 12 9 0.5 a f Means within a column with no common superscript differ significantly (P < 0.05). 1 Means represent 4 pens of 5 chicks per treatment; average initial weight was 101.6 g. 2 Multiple regression of tibia ash (Y; mg) on supplemental P intake (g) from KH 2 PO 4 (X 1 ), DDGS-CONV (X 2 ), HP DDG (X 3 ), and corn germ (X 4 ) yielded the equation: Y = 319 + 353 ± 22X 1 + 212 ± 20X 2 + 203 ± 50X 3 +87 ± 12 X 4 (R 2 = 0.90). The (±) values are standard errors of the regression coefficients. 3 From KH 2 PO 4. 4 DDGS-CONV = distillers dried grains with solubles produced by a conventional dry grind process; HP DDG = high protein distillers dried grains.
EVALUATION OF DISTILLERS DRIED GRAINS WITH SOLUBLES 703 Table 4. Growth performance from 9 to 22 d of age and 21 d tibia ash for chicks in the second P bioavailability assay, experiment 2 1 Tibia ash 2 Dietary Weight Feed Gain:feed treatment gain (g) intake (g) (g/kg) (mg/tibia) (%) 1. Basal diet (B) 267.5 d 408.2 c 656 b 303.3 f 34.4 e 2. B + 0.05% P 3 285.4 bc 435.8 ab 656 b 378.7 bc 38.5 bc 3. B + 0.10% P 3 310.3 a 452.0 a 687 a 436.8 a 41.2 a 4.B+7%DDGS-CONV 4 288.0 bc 430.6 ab 669 ab 336.7 de 36.7 d 5. B + 14% DDGS-CONV 4 308.0 a 451.2 a 683 a 403.1 b 39.3 ab 6. B + 12.5% HP DDG 274.2 d 408.5 c 672 ab 316.4 ef 35.3 cd 7. B + 25% HP DDG 290.8 b 427.1 bc 681 a 358.3 cd 37.9 cd Pooled SEM 5 7 8 10 0.4 a f Means within a column with no common superscript differ significantly (P < 0.05). 1 Means represent 4 pens of 5 chicks per treatment; average initial weight was 86.1 g. 2 Multiple regression of tibia ash (Y; mg) on supplemental P intake (g) from KH 2 PO 4 (X 1 ), DDGS-CONV (X 2 ), and HP DDG (X 3 ) yielded the equation: Y = 297 + 322 ± 20X 1 + 214 ± 21X 2 + 202 ± 30X 3 (R 2 = 0.91). The (±) values are standard errors of the regression coefficients. 3 From KH 2 PO 4. 4 DDGS-CONV = distillers dried grains with solubles produced by a conventional dry grind process; HP DDG = high protein distillers dried grains. Growth performance and tibia ash data are presented in Tables 3 and 4 for the 2 chick P bioavailability assays. In both experiments, a linear increase in weight gain and tibia ash (mg/tibia and %) was observed as the P level was increased by supplementation of KH 2 PO 4. There was also a linear increase in weight gain and tibia ash parameters for the added levels of CONV DDGS, HP DDG, and corn germ. Total P content and P bioavailability values for the 2 experiments are presented in Table 5. The corn germ had higher total P than the CONV DDGS, and the HP DDG contained lower P than the CONV DDGS. The germ fraction contains approximately 90% of the total phytic acid in the corn kernel, whereas the endosperm fraction contributes less P (Martinez Amezcua, 2005). The multiple regression and slope-ratio methods to estimate bioavailability of the P in CONV DDGS, HP DDG, and corn germ yielded regression equations with R 2 values of 0.90 and 0.91 (Table 3 and 4 footnotes). In experiment 1, the bioavailability coefficient for the P in corn germ was much lower than those for CONV DDGS and HP DDG. The decreased P bioavailability coefficient in the corn germ is probably due to majority of the P still being bound by phytic acid because the meal did not undergo fermentation by yeast, as did the CONV and HP DDG. Likewise, the P bioavailability coefficient for HP DDG was similar to CONV DDGS because both products underwent the same fermentation process. When the bioavailability coefficients are multiplied by the total P values, the HP DDG and corn germ were calculated to contain lower levels of bioavailable P than the CONV DDGS. These decreases were due to the reduced P content for HP DDG and the lower P bioavailability for corn germ. Another partial explanation for the decreased P bioavailable content in the HP DDG and corn germ may be attributed to differences in drying conditions for the conventional DDGS in comparison to the HP DDG and the corn germ because they were produced in different plants. Previous studies have shown that variations in drying can affect P bioavailability in DDGS (Martinez Amezcua et al., 2004, Gibson and Karges, 2006). The reasons for or the mechanisms for the effects of drying or heating on P bioavailability are unknown. In experiment 2 where higher levels of HP DDG were fed to obtain greater responses in growth and tibia ash, the results were similar to those obtained in experiment 1. The P bioavailability coefficients and bioavailable P content were slightly higher in experiment 2, but the values for HP DDG relative to conventional DDGS were almost identical to those obtained in experiment 1. Total amino acid levels, amino acid digestibility coefficients, and digestible amino acid concentrations are presented in Table 6. On a total amino acid concentration basis, HP DDG had consistently higher amino acids in comparison to the CONV DDGS and corn germ due to the increased protein content discussed earlier. Although its total amino acid levels were lower, the corn germ contained a relatively high level of lysine and when lysine was calculated as a%of protein, it was found to be almost 2 times greater in corn germ than in the HP DDG. The germ fraction of the corn is the portion of the kernel that contains the majority of the albumin and globular Table 5. Bioavailability of the P in conventional distillers dried grains with solubles (DDGS), high protein distillers dried grains (DDG), and dehydrated corn germ samples Experiment Total Bioavailability Bioavailable and sample P (%) coefficient 1 (%) content 2 (%) Experiment 1 Conventional DDGS 0.76 60 a 0.46 High protein DDG 0.33 58 a 0.19 Corn germ 1.29 25 b 0.32 Experiment 2 Conventional DDGS 0.76 66 0.50 High protein DDG 0.33 63 0.21 a,b Means within a column with no common superscript differ significantly (P < 0.05). 1 Calculated by the slope-ratio method using the multiple linear regression equations in footnote 4 of Tables 3 and 4. 2 Bioavailable content = total P bioavailability coefficient.
704 KIM ET AL. Table 6. Total amino acids, amino acid digestibility coefficients, and digestible amino acid concentrations for conventional distillers dried grains with solubles (DDGS), high protein distillers dried grains (DDG), and dehydrated corn germ Conventional DDGS High protein DDG Corn germ Amino Digestibility Digestible Digestibility Digestible Digestibility Digestible Pooled acid Total coefficient content 1 Total coefficient content Total coefficient content SEM 2 Asp 1.61 77.1 c 1.24 2.27 83.8 b 1.90 1.15 91.9 a 1.06 1.4 Thr 0.96 78.6 b 0.75 1.27 83.1 b 1.06 0.53 90.3 a 0.48 1.8 Ser 1.10 84.5 b 0.93 1.46 87.9 ab 1.28 0.57 93.8 a 0.53 2.0 Glu 3.61 88.1 b 3.18 6.02 92.4 a 5.56 1.88 95.0 a 1.79 1.1 Pro 1.93 87.9 b 1.70 3.19 92.5 a 2.95 0.89 95.2 a 0.85 1.4 Ala 1.77 87.1 b 1.54 2.62 91.0 a 2.38 0.88 91.3 a 0.80 0.9 Cys 0.51 81.3 b 0.41 0.78 91.9 a 0.72 0.31 96.6 a 0.30 2.3 Val 1.28 83.5 b 1.07 1.80 86.8 ab 1.56 0.73 90.5 a 0.66 1.3 Met 0.53 84.4 b 0.45 0.81 90.2 a 0.73 0.27 91.1 a 0.25 0.9 Ile 1.03 85.0 b 0.88 1.35 86.3 b 1.17 0.42 91.0 a 0.38 1.3 Leu 2.98 91.2 a 2.72 4.69 93.7 a 4.39 0.98 92.8 a 0.91 1.0 Tyr 1.02 89.9 a 0.92 1.38 91.6 a 1.26 0.39 93.7 a 0.37 1.5 Phe 1.25 88.1 a 1.10 1.83 91.0 ab 1.67 0.56 91.9 a 0.51 1.2 Lys 0.88 73.9 b 0.65 0.95 73.1 b 0.69 0.80 91.0 a 0.73 1.8 His 0.69 79.8 b 0.55 1.00 85.7 a 0.86 0.42 86.1 a 0.36 1.3 Arg 1.12 88.1 b 0.99 1.38 90.8 b 1.25 1.12 96.5 a 1.08 1.0 Trp 3 0.17 90.9 a 0.15 0.22 89.8 a 0.20 0.14 1.1 a c Means within a row with no common superscript differ significantly (P < 0.05). 1 Digestible content = total bioavailability coefficient. 2 Pooled SEM calculated for digestibility coefficients. Digestibility coefficients are means for 5 cecectomized adult roosters. 3 Trp excreta value for corn germ was too low to be analyzed. proteins as well as the structural proteins, which are high in lysine (Shukla and Cheryan, 2001). When digestibility coefficients were calculated, they were significantly higher for the HP DDG and corn germ than for the CONV DDGS for many amino acids. The higher amino acid digestibility for the HP DDG may have been at least partially due to its lower fiber content compared with CONV DDGS. The reason for the general higher amino acid digestibility of the corn germ is unknown. The digestibility coefficient for lysine was higher for corn germ than for CONV and HP DDG. Lysine is an essential amino acid of particular concern because it has been reported to be highly variable in content and digestibility for CONV DDGS (Cromwell et al., 1993; Spiehs et al., 2002). The higher lysine digestibility of the dehydrated corn germ may be a result of less heat damage during drying when compared with the CONV and HP DDG. Indeed, the corn germ had a lighter color than the CONV and HP DDG. The reason for CONV DDGS having significantly lower digestibility values than the HP DDG for several amino acids is unknown. When both samples were evaluated visually, the HP DDG was lighter in color than the CONV DDGS. Fastinger et al. (2006) concluded that lighter color DDGS samples had more lysine and less variation in lysine digestibilities, whereas darker samples had reduced and more variable lysine digestibility. In this current study, lysine digestibilities were not significantly different for the CONV DDGS and HP DDG, suggesting that heat damage was not the reason for differences in some of the amino acid digestibility coefficients. In addition, the negative effects of heat damage during drying are usually specific to lysine and not the other amino acids. 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