INTRODUCTION. E. J. Kim, P. L. Utterback, and C. M. Parsons1. Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana 61801

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1 Comparison of amino acid digestibility coefficients for corn, corn gluten meal, and corn distillers dried grains with solubles among 3 different bioassays E. J. Kim, P. L. Utterback, and C. M. Parsons1 Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana ABSTRACT The objective of this study was to determine standardized AA digestibility of corn, corn gluten meal, and 3 distillers dried grains with solubles (DDGS) using the precision-fed cecectomized rooster assay (PFR), the standardized ileal AA broiler chicken assay (SIAAD), and a newly developed precision-fed ileal broiler chicken assay (PFC). For the PFR, cecectomized roosters were precision-fed approximately 30 g of feed sample, and excreta were collected 48 h postfeeding. For the SIAAD, 16-d-old broilers were ad libitum fed a semi-purified diet containing the feed samples as the sole source of protein from 17 to 21 d, with ileal digesta collected at 21 d. For the PFC, 22-d-old broiler chickens were precision-fed 10 g of feed and ileal digesta were collected at 4 h postfeeding. For corn, the PFC yielded significantly higher digestibilities than the SIAAD and PFR for several AA. For corn gluten meal, the PFR yielded significantly higher values than the PFC for the majority of the AA, with the SIAAD yielding intermediate values. When 3 DDGS samples were evaluated, the PFR produced higher digestibilities than the PFC for all 3 DDGS samples for most of the AA. When comparing the PFR and the SIAAD, the PFR yielded higher values than the SIAAD for one DDGS, whereas there was generally no significant difference between these 2 methods for the other 2 DDGS samples. The results of this study indicate there were differences among standardized AA digestibility values for the PFR, SIAAD, and PFC in some instances. The differences among methods were not consistent; however, the PFR yielded higher digestibility values than the PFC for 4 of the 5 ingredient samples. Key words: amino acid digestibility, corn, corn gluten meal, distillers dried grains, poultry 2012 Poultry Science 91 : INTRODUCTION Cereal grains, such as corn, are primarily used in poultry diets as a source of carbohydrates and energy; however, due to the high inclusion rate, corn often contributes substantially to the total protein in poultry diets. The high starch content of corn has made it a desirable feedstock for ethanol production. Recently passed legislation has increased ethanol production from corn (Singh et al., 2005). The large increase in ethanol production is also creating a proportional increase in corn distillers dried grains with solubles (DDGS). Corn gluten meal (CGM) is another important coproduct derived from corn that is produced through the wetmilling process. The CGM has been used in poultry diets due to its high protein content (NRC, 1994), high energy content, and high level of xanthophylls (Peter et al., 2000). Methionine or sulfur AA are the first limiting amino acids (AA) in a corn-soybean meal diet for poultry (Fernandez et al., 1994), and CGM has been 2012 Poultry Science Association Inc. Received April 9, Accepted September 1, Corresponding author: poultry@illinois.edu found to be a highly available source of Met (Sasse and Baker, 1973). However, CGM has an imbalanced AA profile, being severely deficient in Lys, Trp, and Arg (Peter et al., 2000). When evaluating AA digestibility of feedstuffs, the precision-fed cecectomized rooster assay (PFR) is a widely accepted method for poultry (Parsons et al., 1982; Ravindran and Bryden, 1999). The largest disadvantage of this assay is the need to surgically modify adult roosters to remove the ceca (Parsons et al., 1982). In addition, there is some concern that this rooster assay may not accurately estimate AA digestibility for growing broilers due to differences in physiology of an adult animal compared with a growing animal (Ravindran and Bryden, 1999; Garcia et al., 2007). Consequently, the standardized ileal AA digestibility chick assay (SIAAD) was developed using 3-wk-old broilers (Lemme et al., 2004). The SIAAD bioassay involves collection of digesta from the ileum section of the small intestine of broiler chickens (Payne et al., 1968). This type of assay is more expensive, time-consuming, and labor intensive than the PFR (Garcia et al., 2007). Therefore, a new precision-fed ileal chick assay (PFC) was developed (Kim et al., 2011). In this type of assay, 3-wk-old broilers are fasted, precision-fed a feedstuff, 3141

2 3142 Kim et al. Table 1. Composition of the experimental diets used in the SIAAD 1 (as-fed basis) Diet 2 Ingredient (%) Corn Corn gluten meal DDGS 1 DDGS 2 DDGS 3 Cornstarch Dextrose Test feed ingredient Solka-Floc Soybean oil Vitamin premix Mineral premix Choline chloride NaCl Limestone Dicalcium phosphate Chromic oxide SIAAD = standardized ileal chick assay; DDGS = distillers dried grains with solubles. 2 All diets were calculated to contain 20% CP, 0.50% available P, and 1.00% Ca, except the corn diet. 3 Purified cellulose, International Fiber Corp., North Tonawanda, NY. 4 Provided per kilogram of diet: retinyl acetate, 4,400 IU; cholecalciferol, 25 μg; dl-α-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. 5 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. and ileal digesta are collected 4 h postfeeding. The PFC should provide a precision-feeding assay with chicks that is rapid, cost-effective, and complementary to the SIAAD due to fewer animals and smaller amounts of feed ingredients required, while hopefully yielding digestibility values that are similar to the SIAAD and PFR. Therefore, the objective of this study was to determine and compare AA digestibility determined for corn, CGM, and 3 DDGS samples using the PFR, SIAAD, and PFC. MATERIALS AND METHODS Feed Sample Analysis A corn, CGM, and 3 DDGS samples were obtained. The 3 DDGS samples were obtained from different ethanol plants. All test feed ingredients were evaluated for N and AA before feeding [AOAC International, 2006: method 990.3, E (a, b, c), respectively] at the Experiment Station Chemical Laboratories, University of Missouri Columbia. SIAAD All animal care, handling, and euthanasia procedures for this and subsequent experiments were approved by the University of Illinois at Urbana-Champaign Animal Care and Use Committee. This assay was conducted using procedures modified from Adedokun et al. (2008). Male Ross Ross 308 broiler chicks were obtained at 1 d of age from a commercial hatchery and fed a cornsoybean meal diet until d 16 that met all nutrient requirements of the NRC (1994). After overnight fasting, the birds were weighed individually and randomized to 5 dietary treatments, with 5 birds per pen, 4 replicate pens per dietary treatments. The experimental diets were formulated to contain approximately 20% CP (with the exception of the corn diet, which was approximately 7% CP), with each of the feedstuffs supplying the entire CP in the diets. Chromic oxide was added to all diets as an indigestible marker at 0.30% of the diet, with all diets being fed in mash form. Compositions of the experimental diets are presented in Table 1. The birds were fed the 5 experimental diets for a 5-d period. On d 21, birds were killed by CO 2 asphyxiation and ileal digesta were collected. PFR A precision-fed rooster assay utilizing cecectomized Single Comb White Leghorn roosters was conducted (Parsons, 1985). After 24 h of feed withdrawal, 20 cecectomized roosters were randomly allocated to groups of 4, for each of the 5 feed ingredients. Each rooster was then precision-fed 30 g of one of the feed samples. All feed ingredients were weighed out to 30 g, but due to differences in sample bulk, not all 30 g were fed for some samples; in the latter cases, all leftover feed was saved and weighed to calculate an exact feed intake. Excreta were then quantitatively collected for a period of 48 h. Endogenous corrections for AA were made using excreta collected from 6 roosters during a fasting period of 48 h. PFC A precision-fed chick assay was conducted following methodology presented by Kim et al. (2011). Eighty Male Ross Ross 308 broiler chicks were obtained at 1 d of age and fed a standard starter diet until d 21. Feed was removed from the birds for an overnight period of at least 8 h to ensure the lower gastrointestinal tract was emptied of feed residues. Chicks were individually

3 weighed and randomized into 20 replicate groups, each containing 4 chicks: 4 groups or 16 total chicks per test ingredient. Each chick was then precision-fed 10 g of one of the 5 feed samples mixed with 0.3% chromic oxide, based on the treatment randomization. Each replicate group was then placed into a battery cage, and the chicks were allowed free access to water during this time. Four hours after feeding, the chicks were euthanized via CO 2 asphyxiation and ileal digesta were collected and pooled per replicate group. Sampling, Ileal Digesta, and Excreta Processing For the SIAAD and the PFC, the contents of the ileum were considered to be the portion of the small intestine from the Meckel s diverticulum to the approximately 1 cm proximal to the ileo-cecal junction. The ileal digesta from birds within pens or groups were pooled, frozen, and stored at 20 C until they were processed. For the rooster assay, the excreta collected were also frozen and stored at 20 C until processing. All ileal and excreta samples were lyophilized, ground by using a mortar and pestle, and then sent to the University of Missouri Experiment Station and Chemical Laboratories for AA and chromium analysis (only SIAAD and PFC digesta were analyzed for chromium; AOAC International, 2006: method , ICP method). Calculations Amino acid digestibility for the SIAAD and PFC were calculated using the following formulas by Moughan et al. (1992). The apparent ileal AA digestibility coefficients obtained from the SIAAD were standardized by using ileal endogenous AA (IEAA) flow values from 21-d-old broiler chicks fed a nitrogen-free diet (Adedokun et al., 2007). The apparent ileal AA digestibility coefficients obtained from the PFC were standardized using IEAA values from chicks precision-fed a nitrogenfree diet (Kim et al., 2011). For the SIAAD, the diet was the semi-purified diet with the feed ingredient as the sole source of protein. The diets for the PFC and PFR were the feed ingredient itself. Values from the PFR were standardized using an endogenous AA calculated from fasted roosters. Apparent ileal AA digestibility = [1 (chromium in diet/chromium in digesta) (AA in digesta/aa in diet)] 100. Standardized ileal AA digestibility, % = apparent digestibility + [(IEAA flow, g/kg of DM intake)/(aa in the diet or feed ingredient, g/kg of DM intake)] 100. AMINO ACID DIGESTIBILITY COMPARISONS For the rooster assay, standardized AA digestibility values were calculated with the following formula: standardized AA digestibility, % = {[AA intake (mg) AA in excreted (mg) + endogenous AA (mg)]/aa intake (mg)} 100. Statistical Analysis All AA digestibility data from all assays were analyzed by using PROC GLM (SAS, 2004) as a completely randomized design. For the PFR, experimental unit was the individual rooster with 4 per feed ingredient. For the SIAAD and PFC, the experimental unit was the replicate group (pen), which was 4 in both instances. Differences among treatment means were determined by using the PDIFF option in the least squares means (LSMEANS) procedure of GLM. The level of significance was set at P RESULTS AND DISCUSSION 3143 Total AA concentrations for the corn, CGM, and DDGS samples are presented in Table 2 and standardized AA digestibility coefficients for the 5 samples are presented in Tables 3 and 4. Values for Gly are not presented in this study due to formation of Gly from uric acid during acid hydrolysis and therefore yielding inaccurate digestibility values in the PFR. Total Trp levels are presented in Table 2, but digestibility coefficients are not presented for Trp due to levels being too low to be detected in both ileal chick assays. When the corn sample was fed in the 3 assays, there was a greater variability (larger SEM) in the SIAAD AA digestibility values when compared with the PFR and PFC (Table 3). When comparing the PFC to the other 2 methods, it generally yielded numerically higher AA digestibility values with the difference being significant (P 0.05) for Ile and Lys. The PFC value for Met was also only significantly higher than the SIAAD value. Whereas the PFC yielded higher digestibilities, there were no differences between the PFR and SIAAD for any of the other AA. The increased AA digestibility for the PFC for corn may be at least partially due to an overestimation of the endogenous correction being used to standardize the AA coefficients, which resulted in an overestimation of calculated AA digestibility (Ravindran and Bryden, 1999; Kadim et al., 2002; Lemme et al., 2004). For example, standardized Met digestibility was calculated to be in excess of 100% for the PFC. Because corn is low in CP and AA levels (resulting in low intake), any error in the IEAA correction will have a large effect on AA digestibility values (Ravindran et al., 2005). Several studies have indicated that at low protein/aa intake, apparent digestibility estimates will be lower due to greater proportion of the endogenous protein present at the terminal ileum (Fan et al., 1994; Angkanaporn

4 3144 Kim et al. Table 2. Total amino acid (AA) concentrations (%) in corn, corn gluten meal (CGM), and 3 corn distillers dried grains with solubles (DDGS) samples, as-fed basis Item Corn CGM DDGS 1 DDGS 2 DDGS 3 Indispensable AA Arg His Ile Leu Lys Met Phe Thr Trp Val Dispensable AA Ala Arg Asp Cys Glu Pro Ser Tyr CP et al., 1997; Ravindran et al., 2005). Moter and Stein (2004) reported that as feed intake increased, IEAA flow was found to decrease when expressed relative to DM intake in growing pigs. The above studies indicate that IEAA flow can be affected by several factors and can have a large effect on AA digestibility values. Standardized AA digestibility of CGM was greater (P 0.05) for the PFR and SIAAD than the PFC for most of the AA. Lysine was an exception in which there were no differences among assays. The PFR also yielded significantly greater digestibility values for several AA when compared with the SIAAD. For DDGS, total AA concentrations varied among the 3 samples (Table 2). For example, total Lys content ranged from 0.67% (DDGS 2) to 1.01% (DDGS 1). When calculated as a percentage of CP, the Lys/CP ratio for DDGS 1 and 2 were 3.7 and 2.5%, respectively, suggesting increased heat damage or overheating of DDGS 2 compared with DDGS 1 (Martinez Amezcua and Parsons, 2007; Stein et al., 2009). When comparing AA digestibility values among the DDGS samples (Table 4), the PFR consistently yielded higher digestibility values for DDGS 1 when compared with the PFC, with the SIAAD generally yielding intermediate values. The SIAAD also Table 3. Comparison of standardized amino acid (AA) digestibility coefficients (%) for corn and corn gluten meal determined by 3 different methods Corn Corn gluten meal Item SIAAD 1 SEM PFC 2 SEM PFR 3 SEM SIAAD SEM PFC SEM PFR SEM Indispensable AA Arg ab b a 0.7 His 85.3 a a b a b a 0.7 Ile 85.6 b a b a b a 0.5 Leu a b a 0.2 Lys 74.4 b a b Met 89.1 b a ab b c a 0.2 Phe a b a 0.3 Thr b b a 0.8 Val b c a 0.5 Mean Dispensable AA Ala a b a 0.2 Asp b c a 0.4 Cys a b a 0.9 Glu b c a 0.2 Pro b c a 0.4 Ser a b a 0.7 Tyr 87.0 ab a b b c a 0.4 Mean a c Means within a row within sample with no common superscripts are significantly different (P 0.05). 1 SIAAD = standardized ileal chick assay; mean of 4 replicate pens of 5 broiler chickens. 2 PFC = precision-fed ileal chick assay; mean of 4 replicate pens of 4 broiler chickens. 3 PFR = precision-fed cecectomized rooster assay; mean of 4 individual roosters.

5 AMINO ACID DIGESTIBILITY COMPARISONS 3145 Table 4. Comparison of standardized amino acid (AA) digestibility coefficients (%) for 3 different corn distillers dried grains with solubles (DDGS) samples determined by 3 different methods DDGS 1 DDGS 2 DDGS 3 Item SIAAD 1 SEM PFC 2 SEM PFR 3 SEM SIAAD SEM PFC SEM PFR SEM SIAAD SEM PFC SEM PFR SEM Indispensable AA Arg 77.6 ab b a b b a His 74.4 a b a b b a a b ab 0.8 Ile 72.7 ab b a c b a Leu 82.1 ab b a b c a a b a 0.9 Lys 61.7 b b a b a a Met 78.4 b b a c b a Phe 80.9 a b a a b a a b a 1.1 Thr 66.4 ab b a b b a Val 71.7 ab b a b b a Mean Dispensable AA Ala 80.7 ab b a a b a a b a 1.0 Asp 67.9 a b a b b a a b a 1.6 Cys 72.7 a b a b c a a b a 2.7 Glu 79.1 ab b a b c a a b a 1.2 Pro 80.2 a b a a b a a b a 1.2 Ser 77.1 a b a a b a Tyr 81.6 ab b a a b a Mean a c Means within a row within sample with no common superscripts are significantly different (P 0.05). 1 SIAAD = standardized ileal chick assay; mean of 4 replicate pens of 5 broiler chickens. 2 PFC = precision-fed ileal chick assay; mean of 4 replicate pens of 4 broiler chickens. 3 PFR = precision-fed cecectomized rooster assay; mean of 4 individual roosters.

6 3146 Kim et al. yielded higher values than the PFC for DDGS 1 for several AA. The PFR and SIAAD values did not differ, with the exception of Met, which was significantly lower. Lysine digestibility was also significantly lower for the SIAAD. For DDGS 2, the PFR again yielded significantly higher digestibilities than the PFC for all AA evaluated with the exception of Lys. Values for the PFR were also higher than those for the SIAAD for several AA. Differences between the SIAAD and PFC were not consistent. The SIAAD yielded a very low digestibility value for Lys (37%), which was lower (P 0.05) than the other 2 methods. The low Lys digestibility may be due to an unusually high Lys concentration in the ileal digesta; reanalysis of the digesta sample confirmed the value. When standardized AA digestibilities were determined for DDGS 3, values for the PFR and SIAAD were significantly higher than the PFC for several AA, but there were no differences among methods for most of the practically important indispensable AA such as Met, Cys, Lys, and Thr. Lysine has always been an AA of particular interest in DDGS samples due its high variability in concentration and digestibility (Lumpkins and Batal, 2005; Batal and Dale, 2006). In this current study, there was again a wide variation of in total Lys concentration and digestibility among the samples and also among digestibility methods. As mentioned earlier, total Lys content was found to range from 0.67% (DDGS 2) to 1.01% (DDGS 1; Table 2). The NRC (1994) reports a total Lys content of 0.75% in DDGS, which falls within the range of our analyzed values. Similar results have been reported in earlier studies. Batal and Dale (2006) reported total Lys content in 8 DDGS samples to range from 0.39 to 0.86%, with an average Lys digestibility of 69.6%. Fastinger et al. (2006) reported total Lys content of 5 DDGS samples to range from 0.48 to 0.76%, with an average Lys digestibility of 76.6%. More recently, Pahm et al. (2009) reported total Lys content of 7 DDGS samples to range between 0.65 to 0.94%, with an average of 0.77% and Lys digestibility averaging 61.4%. The DDGS 1 in the current study had a Lys digestibility that ranged from 58% (PFC) to 70% (PFR), whereas DDGS 2 had the lowest Lys digestibility at 37% (SIAAD), but yielded higher values for the other assays (58% for both the PFC and the PFR). The lowest range or variation in Lys digestibility among methods was observed for DDGS, with values ranging from 64% (PFR) to 66% (SIAAD and PFC). All 3 DDGS samples were commercially available samples and were obtained from different ethanol plants. All 3 samples were observed to be different in color. Of the 3 samples evaluated in this study, DDGS 2 had the darkest color and also had the lowest Lys digestibility, particularly for the SIAAD. The latter DDGS also had the lowest Lys/CP ratio. These results suggest that the DDGS 2 may have been more heat damaged than DDGS 1 and 3. It has been proposed that the color of the DDGS may be indicative of lower Lys content and digestibility (Ergul et al., 2003; Fastinger et al., 2006). The darker color may indicate increased levels of Maillard reaction products, which are produced from the reaction between a reducing sugar and a free amino group, usually the epsilon amino group of Lys, during heat treatment. During the dry-grind processing scheme, the wet distillers grains are mixed with the solubles fraction, which contains a high concentration of reducing sugars, and the mixture is then dried at high temperatures to decrease the moisture content of the wet grains and solubles (Kwiatkowski et al., 2006). This part of the ethanol production process is not highly regulated and can produce DDGS of varying color due to differences in drying temperature and length (Belyea et al., 2004). Whereas the drying processes and solubles contents for our 3 DDGS samples are unknown, variation among these 2 variables may account for all or part of differences in Lys content and digestibility observed in the current study. Several differences in standardized AA digestibility values were observed among the 3 methods and the reasons for the differences are unknown. The differences among methods were not consistent, although the PFR generally yielded digestibility values that were higher than the PFC. Digestibility values determined with the PFR and SIAAD were generally not significantly different. Some other studies or reviews have reported that digestibility values for several ingredients are often higher when based on excreta collection versus ileal digesta collection (Ravindran and Bryden, 1999; Garcia et al., 2007; Adedokun et al., 2009). Of course, a large part of the reason for the higher values in excreta collection assays using conventional chickens is microbial degradation/metabolism of AA in the hindgut (primarily ceca). However, excreta digestibility values for cecectomized roosters were also reported to often be higher than ileal values in the Garcia et al. (2007) and Adedokun et al. (2009) studies and also in the current study. One possible reason, particularly for differences between the rooster and chick assays, is the difference in collection sites (excreta versus ileal). In the current study, ileal digesta were collected from Meckel s diverticulum to 1 cm proximal to the ileo-cecal junction. Several studies have indicated a difference in ileal AA digestibility based on site of sampling in the ileum (Kadim and Moughan, 1997; Kluth et al., 2005; Rezvani et al., 2008). These studies have indicated that there is disappearance of AA from the proximal ileum and that AA digestibility values determined from collection of ileal digesta that includes the proximal ileum (as is usually done) may be underestimated. In other words, some AA in the proximal ileum would have disappeared or would have been digested if they had been allowed to traverse the central and distal ileum. The latter may at least partially explain why AA digestibility values were sometimes higher in the PFR assay (excreta collection) than in the SIAAD and PFC (proximal, central, and distal ileal digesta collection) in the current study.

7 Another possible reason, although unlikely, for the differences between the rooster and chick assays is bird age. It has been shown that N and AA digestibility in very young chicks is lower than in older chicks (Noy and Sklan, 1995; Batal and Parsons, 2002; Adedokun et al., 2008). This effect of age, however, is only for the first 10 to 15 d, with N and AA digestibility not changing with age after that time. Because the chicks used for AA digestibility in the current study were 21 d of age, it is unlikely that bird age accounted for a substantial amount of the difference in AA digestibility between chicks and roosters. In conclusion, all of the methods evaluated herein (PFR, SIAAD, and the new PFC) seem to be acceptable methods for determining AA digestibility in poultry because although differences were sometimes observed among assays, these differences were not consistent. 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