Ileal digestibility of amino acids in pea protein isolates, wheat-corn distillers dried grains with solubles, and short-season corn fed to broiler chicks

Ileal digestibility of amino acids in pea protein isolates, wheat-corn distillers dried grains with solubles, and short-season corn fed to broiler chicks N. K. Nandha,* T. A. Woyengo,* R. L. Payne,† and C. M. Nyachoti*1 *Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2; and †Evonik Industries, Kennesaw, GA 30144 ABSTRACT The apparent ileal digestibility (AID) of amino acids (AA) in 4 pea protein isolates [PPI; experiment (Exp.) 1], 5 wheat- and corn-derived distillers grains with solubles (wcDDGS; Exp. 2), and 5 shortseason corn (Exp. 3) samples for broiler chickens were determined. In addition, a reference wheat sample was included in each experiment to measure the repeatability of the ileal digestibility assay used. Birds (n = 180 for Exp. 1 and n = 216 for Exp. 2 or 3) were fed test diets from d 15 to 21 of age. Reference wheat and PPI were included in test diets at 91.7 and 25%, respectively, as the sole source of AA, whereas wcDDGS and corn were combined with wheat in test diets at 47.7% test ingredient (wcDDGS or corn) and 51% wheat as the sources of AA. Chromic oxide at 0.3% was added in all diets as

the indigestible marker. Each test diet was randomly assigned to 6 cages of 6 male birds each. On d 21, birds were killed and ileal digesta were collected to determine the AID of AA. The mean AID values for indispensable AA ranged from 86.0% (Thr) to 94.7% (Arg) for PPI, 50.7% (Lys) to 79.8% (Leu) for wcDDGS, and 73.9% (Thr) to 95.3% (Arg) for corn. Overall, the CV range for AID of AA was widest for wcDDGS (8.1% for Met to 29.4% for Lys) followed by corn (3.0% for Met to 10.7% for Thr) and then PPI (2.7% for Lys to 6.1% for Thr). For wcDDGS and corn, the within-sample variation (assay condition) was more than between-sample variation (feed differences), whereas the reverse was true for PPI. No differences were detected in the AID of CP and AA for reference wheat among experiments.

Key words: broiler, ileal amino acid digestibility, pea protein isolate, wheat and corn-derived distillers grains with solubles, corn 2013 Poultry Science 92:184–191 http://dx.doi.org/10.3382/ps.2012-02498

INTRODUCTION

and corn are available for formulating poultry feeds in North America. Peas have high protein content (Bandegan et al., 2011). However, AA digestibility in peas for nonruminants such as poultry is limited by antinutritional factors such as fiber, trypsin inhibitors, and tannins (Fan and Sauer, 1999; Gabriel et al., 2008). To make pea proteins more attractive for use in nonruminants, pea protein isolates (PPI) that are almost devoid of these antinutritional factors have been obtained from peas (Fredrikson et al., 2001). The digestibility of AA in PPI for pigs has been determined (Le Guen et al., 1995); however, no such data are available for poultry. In recent years, increased use of ethanol as a biofuel has led to large availability of DDGS, which can be used in formulation of poultry diets. Studies have demonstrated that DDGS can be incorporated at modest levels into poultry diets without deleterious effects on bird performance (Thacker and Widyaratne, 2007; Wang et al., 2007; Youssef et al., 2008). In modern ethanol plants, cereal feedstock is exposed to more controlled processes of heating and drying (Światkiewicz and Koreleski, 2008), thereby yielding more valuable

Amino acids (AA) are the second most expensive nutrients in practical poultry diets after energy and if not supplied in correct dietary amounts, they can contribute to environmental pollution due to excessive nitrogen excretion. Therefore, to minimize the cost of feeding and the potential negative impact of AA on the environment as well as ensure optimal and more predictable growth performance, it is critical to closely match dietary AA supply with requirements. This can be achieved if the available AA contents in feedstuffs used to formulate poultry diets are known. Amino acid digestibility assay is a more practical method of estimating AA availability in feedstuffs than other methods (Stein et al., 2007). Pea, corn, and wheat by-products from the ethanol industry (dried distillers grains with solubles; DDGS), ©2013 Poultry Science Association Inc. Received May 25, 2012. Accepted September 30, 2012. 1 Corresponding author: [email protected]

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DDGS (often referred to as new generation DDGS). Amino acid digestibilities of old generation corn- and wheat-derived DDGS fed to poultry have been determined (Fastinger et al., 2006; Thacker and Widyaratne, 2007; Bandegan et al., 2009), but there are no reports on digestibility of AA in DDGS produced from modern ethanol plants that use blends of corn and wheat (wcDDGS) as a fermentable cereal base. In addition, little information is available on factors (feed or bird) that affect the overall CV that is associated with the digestibilities of AA in DDGS samples. Corn is the most widely used cereal in poultry diets. It was thought to be the most consistent cereal in terms of nutrient value. It has, however, been demonstrated that field location and corn heat unit (unit of heat that is available for growth and development of corn) rating of corn cultivars can affect the nutrient composition of corn (Opapeju et al., 2007). Increased production of high-yielding, low-corn-heat-unit-rated cultivars (short-season corn) in Manitoba has increased the potential of the corn to be used in broiler diets. However, digestibilities of AA in short-season corn for broilers have not been determined. Therefore, it is critical to evaluate CP and AA digestibilities and their associated variability among corn grown in different regions. The objective of the current study was to determine the apparent ileal digestibility (AID) of CP and AA and their associated CV in PPI, wcDDGS, and shortseason corn samples fed to broiler chicks.

MATERIALS AND METHODS Diets Four PPI (Nutri-pea Ltd., Portage La Prairie, Manitoba, Canada), 5 wcDDGS (from Husky’s Mohawk Ethanol plant at Minnedosa, Manitoba, Canada), and 5 corn samples grown in different regions of Manitoba were assayed in 3 separate experiments: one experiment for each feedstuff. The PPI samples were collected from 4 different processing periods; wcDDGS samples were collected from 5 different fermentation batches with different grain source and processing days; and corn samples were obtained from 5 different locations in Manitoba. In addition, a sample of reference wheat (AC Barrie) obtained from a local farm was included in each experiment to measure the repeatability of ileal digestibility assays used. Test diets in experiment (Exp.) 1 contained PPI (25%) as the sole source of AA. Test diets in Exp. 2 contained 51% wheat and 47.7% wcDDGS as the sources of AA, whereas diets in Exp. 3 contained 51% wheat and 47.7% corn as the sources of AA. The reference wheat assayed in each experiment was included at 91.7% as the sole source of AA. All diets contained chromic oxide (0.3%) as an indigestible marker and were balanced for minerals and vitamins as per NRC (1994) recommendations.

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Birds and Conduct of Experiment The experimental protocol was reviewed and approved by the Animal Care Protocol Management and Review Committee of the University of Manitoba, and birds were cared for according to the guidelines of the Canadian Council on Animal Care (CCAC, 2009). One hundred eighty 1-d-old male broilers chicks were used in Exp. 1, whereas two hundred sixteen 1-d-old male broilers chicks each were used in Exp. 2 and 3. The birds (Ross 308, Aviagen) were obtained from a local hatchery (Carlton Hatchery, Grunthal, Manitoba, Canada) and were housed in Petersime battery brooders (Petersime Incubator Co., Gettysburg, OH) in a room with continuous fluorescent lighting. Room temperature was maintained at 32, 28, and 24°C during wk 1, 2, and 3, respectively. From d 1 to 14, birds were fed a commercial starter diet (FeedRite, Ridley Inc., Winnipeg, Manitoba, Canada) in the form of crumbles (3,100 kcal/kg, 19% CP). On d 14, birds were weighed and distributed (6 birds/cage) into 30, 36, and 36 cages with similar BW for Exp. 1, 2, and 3, respectively. Six replicate cages were randomly assigned to each of the test diets and fed from d 15 to 21 of age. Birds had free access to feed and water throughout the study period. On d 21, birds were killed by cervical dislocation and the digesta samples from the ileum (from Meckel’s diverticulum to a point 4 cm proximal to the ileocecal junction) were collected by gently squeezing the contents of the ileum into sample bags. Digesta from birds within a cage were pooled into 1 bag and frozen immediately after collection and subsequently freeze-dried. The dried ileal digesta were stored in airtight bags at −4°C until required for chemical analysis.

Chemical Analysis Raw feed ingredients, test diets, and digesta samples were finely ground using a coffee grinder (CBG5 Smart Grind; Applica Consumer Products Inc., Shelton, CT). Dry matter was determined according to the method of AOAC International (2000, procedure 934.01), and CP (N × 6.25) was determined using the Leco N analyzer (model CNS-2000, Leco Corp., St. Joseph, MI). Amino acid concentrations of the diet and digesta were determined by Evonik Industries (Hanau, Germany) using ion-exchange chromatography with postcolumn derivatization with ninhydrin (Llames and Fontaine, 1994). Sulfur-containing AA (Met and Cys) were first oxidized with performic acid, which was subsequently neutralized with sodium metabisulfite (Commission Directive, 1998). Amino acid concentrations were quantified with the internal standard method by measuring the absorption of reaction products with ninhydrin at 570 nm. Chromium was analyzed after the samples were ashed at 600°C for 12 h in a muffle furnace, using inductively coupled plasma mass spectrometry (ICP-

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AES Vista, Varian, Palo Alto, CA) according to AOAC International (2005, procedure 985.01).

Table 1. Dry matter, CP, and amino acid (AA) composition of reference wheat fed to broiler chicks

Digestibility Calculations

Item

The AID estimates of protein and AA in PPI (Exp. 1) and in the reference wheat were calculated using the direct method (Fan and Sauer, 1995) as follows:

AID =

(AA/M)d − (AA/M)id , (AA/M)d

where (AA/M)d = ratio of AA to marker concentration in diet and (AA/M)id = ratio of AA to marker concentration in ileal digesta. Because difference method is more appropriate than direct method for feedstuffs with poor palatability or with low protein content (Fan and Sauer, 1995), the diets used in Exp. 2 and 3 were a wheat-based diet in which wheat as the sole source of protein, and a wheat- and test ingredient- (wcDDGS or corn) based diet in which wheat and the test ingredient were the sole sources of protein. Thus, the AID coefficients of protein and AA in wcDDGS (Exp. 2) or corn (Exp. 3) were determined by the difference method (Fan and Sauer, 1995), with the wheat-based diet as the basal diet, using the following equation: DA = (DD − DB × SB)/SA, where DD = AID of an AA in the test diet (%); DB = AID of an AA in the wheat (%); SB = contribution level of an AA from the wheat to the test diet, SB = 1 − SA (decimal percentage); DA = AID of an AA in the test feed ingredient (wcDDGS or corn; %); and SA = contribution level of an AA from the test feed ingredient (wcDDGS or corn) to the test diet (decimal percentage).

Statistical Analysis Digestibility data were analyzed using the GLM procedure (SAS software release 9.1, SAS Institute Inc., Cary, NC) as a completely randomized design. The nested procedure was applied to further analyze the random feed samples and bird/cage subsampling effects on the total variation observed. For a better demonstration of variability, the components of total CV (%) associated with the AID for each AA across different feed samples are included as variance due to the samples (σs2 ) and cages within samples (σe2 ).

RESULTS AND DISCUSSION Crude protein and AA concentrations in the reference wheat sample are presented in Table 1, whereas the CP and AA contents in PPI, wcDDGS, and corn are presented in Table 2. The CP and AA concentra-

DM CP (N × 6.25) Indispensable AA  Arg  His  Ile  Leu  Lys  Met  Phe  Thr  Val Dispensable AA  Ala  Asp  Cys  Glu  Gly  Pro  Ser

% DM basis 94.9 15.3   0.59 0.34 0.40 0.98 0.38 0.31 0.72 0.49 0.50   0.58 0.74 0.36 4.96 0.59 1.58 0.69

tions in the reference wheat compared well with the values for the wheat assayed previously in our laboratory (Bandegan et al., 2009). The CP and AA contents in PPI were higher than published values of CP and AA in whole pea (Owusu-Asiedu et al., 2002; Ravindran et al., 2005; Bandegan et al., 2011), which was due to the dilution of protein in the whole peas with starch and other components present in pea. Also, the CP and AA contents in PPI were higher than published values of CP and AA in pea protein concentrate (Valencia et al., 2009). The PPI used in the current study was prepared using a wet process, which mainly concentrates proteins, whereas the pea protein concentrates used in the study of Valencia et al. (2009) were produced using a dry process (air classification technique), which concentrates proteins as well as antinutritional factors (Gueguen, 1983). Therefore, the lower CP and AA contents for pea protein concentrate compared with the PPI was due to the dilution of protein with the antinutritional factors. Leucine, Arg, and Lys were the most abundant indispensable AA, whereas Met was the least abundant indispensable AA in PPI. Other studies (Igbasan et al., 1997; Ravindran et al., 2005; Bandegan et al., 2011) have also reported similar AA profiles in whole peas, implying that the removal of starch and antinutritional factors from peas by the wet process does not affect AA acid composition of the resulting PPI. The CP and AA concentrations of corn samples were similar to the values that were reported in previous studies (Ravindran et al., 1999; Opapeju et al., 2007). The CP and AA levels in wcDDGS were closer to values reported for corn DDGS (Fastinger and Mahan, 2006; Fastinger et al., 2006; Stein et al., 2006) than for wheat DDGS (Bandegan et al., 2009). The DDGS assayed in the current study was derived from a blend of approximately 75% corn and 25% wheat, so the similarity between

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Table 2. Dry matter, CP, and amino acid (AA) composition in pea protein isolate (PPI) distillers dried grains with solubles derived from a blend of wheat and corn (wcDDGS) and corn fed to broilers, % DM basis1 PPI1 Item DM CP Indispensable AA  Arg  His  Ile  Leu  Lys  Met  Phe  Thr  Val Dispensable AA  Ala  Asp  Cys  Glu  Gly  Pro  Ser

wcDDGS2

Corn3

Range

Mean

CV%

 

Range

Mean

CV%

 

Range

Mean

CV%

94.6 to 95.3 84.4 to 86.0

94.9 84.9   6.40 1.91 3.51 6.52 5.64 0.80 4.16 2.68 3.52   3.42 8.90 0.78 14.3 2.88 3.25 3.75

0.30 0.89   8.60 8.99 14.4 6.84 5.92 2.57 6.39 4.83 12.93   3.52 5.45 7.33 4.28 8.34 4.41 4.90

   

92.8 to 93.5 30.7 to 31.9   1.17 to 1.27 0.89 to 0.94 1.36 to 1.44 3.61 to 3.95 0.79 to 0.85 0.71 to 0.79 1.58 to 1.61 1.11 to 1.22 1.53 to 1.59   2.07 to 2.27 1.89 to 1.98 0.64 to 0.71 6.43 to 7.24 1.21 to 1.25 2.64 to 2.79 2.39 to 1.52

93.1 31.4   1.23 0.92 1.40 3.76 0.82 0.75 1.60 1.16 1.57   2.15 1.96 0.67 6.84 1.23 2.73 1.44

0.40 1.45   2.93 2.15 2.80 3.65 2.65 4.13 0.74 3.12 1.41   3.85 1.79 3.83 4.43 1.49 2.15 3.48

   

88.0 to 90.5 6.22 to 7.51   0.30 to 0.38 0.20 to 0.28 0.25 to 0.32 1.01 to 1.18 0.20 to 0.26 0.18 to 0.28 0.37 to 0.47 0.28 to 0.39 0.31 to 0.36   0.57 to 0.75 0.47 to 0.62 0.15 to 0.24 1.44 to 1.94 0.25 to 0.30 0.66 to 0.83 0.32 to 0.46

89.9 6.77   0.34 0.23 0.29 1.12 0.23 0.21 0.42 0.35 0.34   0.66 0.55 0.19 1.69 0.28 0.77 0.40

0.90 8.06   9.50 11.8 9.88 9.21 9.06 18.0 11.9 13.2 5.74   14.2 12.5 19.2 14.4 8.24 12.9 15.3

5.85 1.76 2.98 6.19 5.34 0.77 3.98 2.54 3.04

to to to to to to to to to

7.15 2.14 4.18 7.14 6.11 0.82 4.53 2.85 4.10

3.28 to 3.54 8.35 to 9.54 0.72 to 0.85 13.5 to 14.9 2.67 to 3.22 3.08 to 3.43 3.53 to 3.97

 

 

                               

 

 

                               

1Four

different samples of PPI were analyzed. different samples of wcDDGS were analyzed. 3Five different samples of corn were analyzed. 2Five

wcDGGS used in the current study with corn DDGS is not surprising. The CP and AA contents in wcDDGS were higher than respective contents in wheat and corn samples, and this was because of the fermentation of starch into alcohol and carbon dioxide, which are removed to leave behind concentrated amounts of other nutrients. Other studies (Thacker and Widyaratne, 2007; Lan et al., 2008; Bandegan et al., 2009) also reported a 2- to 3-fold higher AA content in DGGS than in grains from which the DDGS were derived. The AID of CP and AA in reference wheat, and in PPI, corn, and wcDDGS are presented in Tables 3 and 4, respectively. The AID of CP and AA of the reference wheat were similar to the values reported by Bandegan et al. (2009) for the same variety of wheat fed to broiler chicks. The AID of CP and AA of the reference wheat were also similar to the AID coefficients reported by others (Huang et al., 2005; Ravindran et al., 2005) for wheat fed to broilers. The AID coefficients in the reference wheat were determined in each of the 3 independent experiments to assess the repeatability of the broiler ileal digestibility assay. No differences (P < 0.05) were detected in the AID of CP and AA among experiments. The variance components showed higher variation from within assays rather than between assays. Thus, these findings prove the reproducibility of the ileal digestibility assay used in our laboratory and confirm that the digestibility values obtained in different experiments are comparable. Similar conclusions have also been previously drawn in our laboratory (Bandegan et al., 2009). In PPI, Thr was the least digestible AA, whereas Lys and Arg were the most digestible AA among the indispensable AA. The higher AID of Lys and Arg for PPI

could partly have been due to a higher content of these AA in PPI. Apparent ileal digestibility of an AA is positively related to dietary content of the AA (Fan et al., 1994). The low digestibility of Thr in PPI could be attributed to the fact that it is a major indispensable AA in gut secretions (Siriwan et al., 1993; Ravindran and Hendriks, 2004; Ravindran et al., 2005). Bandegan et al. (2011) have also reported Thr as the least digestible AA and Lys and Arg as the most digestible AA in whole pea fed to broilers. No published data are available on AA digestibility for PPI fed to broilers. The AID of CP and AA in PPI were higher than the values reported for whole peas (Bandegan et al., 2011) and for pea protein concentrates (Valencia et al., 2009) fed to broilers. This is attributed to the fact that PPI is almost devoid of antinutritional factors such as fiber, phytic acid, and tannins, which are known to reduce CP and AA digestibilities in nonruminants such as poultry (Cowieson et al., 2006; Ravindran et al., 2006; Woyengo and Nyachoti, 2012). Arginine, Leu, and Met were the most digestible indispensable AA, whereas Thr was the least digestible indispensable AA in corn. The higher AID of Leu could have been due to its high concentration in corn (Table 2), whereas the lower AID of Thr could have been due to its high concentration in the gut secretions as described above. However, it is difficult to explain the higher AID of Arg and Met because their content in corn was low (Table 2). Nonetheless, Adedokun et al. (2008) also reported Arg, Leu, and Met to be the most digestible indispensable AA, and Thr to be the least digestible indispensable AA in regular corn fed to broilers. However, the AA digestibility values for corn in the current study were higher than those reported by Ad-

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Table 3. Apparent ileal CP and amino acid (AA) digestibilities and their associated CV determined in broiler chicks fed diets containing a reference wheat sample in 3 different assays1 Variance component3

Assay

Items CP Indispensable AA  Arg  His  Ile  Leu  Lys  Met  Phe  Thr  Val Dispensable AA  Ala  Asp  Cys  Glu  Gly  Pro  Ser 1Same

1

2

3

Average

CV,2 %

85.0

84.0   79.4 84.2 85.7 86.4 76.2 89.1 87.3 74.1 82.1   77.3 75.6 86.4 94.5 79.0 93.1 83.1

86.6   81.9 84.8 87.2 87.8 78.6 90.1 88.4 77.0 83.7   80.2 77.1 87.3 95.1 81.0 93.6 84.8

85.2   80.8 84.8 86.0 86.9 77.3 89.9 87.8 74.8 82.5   78.7 76.4 86.4 94.8 80.0 93.4 83.5

3.2   3.8 3.2 3.2 2.3 3.9 1.9 2.4 5.2 3.1   4.1 5.2 3.1 0.8 3.0 0.8 3.0

81.0 85.4 85.0 86.3 77.2 90.5 87.6 73.4 81.6 78.6 76.5 85.6 94.9 80.0 93.5 82.7

Between assays σs2

( )

28.1   3.2 0.0 10.6 7.9 2.2 9.1 0.0 31.8 13.5   18.2 0.0 6.8 16.3 3.4 0.0 21.4

Within assays σe2

( )

71.9   96.8 100.0 89.4 92.2 97.8 90.9 100.0 68.3 86.5   81.8 100.0 93.2 83.7 96.6 100.0 78.6

P-value 0.09   0.34 0.67 0.24 0.28 0.36 0.26 0.56 0.07 0.21   0.16 0.40 0.29 0.18 0.34 0.46 0.14

sample of wheat was fed to 6 cages per assay (each with 6 birds). σe2 − σs2

× 100%, where σs2 = variance due to samples; σe2 = variance due to cages within samples; and γ = average. γ 3Percentage contribution to the total variation calculated as σ2 / σ2 + σ2 and σ2 / σ2 + σ2 for samples and cages within samples, respectively. s s e e s e 2Total

CV =

(

)

edokun et al. (2008), which could partly have been due to differences in the cultivars used as has been reported previously (Opapeju et al., 2007) or due to differences in the methods used to determine AA digestibility. The difference method was used in the current study, whereas Adedokun et al. (2008) used the direct method to determine AA digestibility. Most of the digestibility data available for corn have been determined either

(

)

in cecectomized roosters (Sibbald, 1979; Green et al., 1987) or in grower-finisher broilers (Huang et al., 2005, 2006), and hence it is difficult to compare AA digestibility values obtained in 3-wk-old broilers with those obtained using older birds. In wcDDGS, Leu, Met, and Phe had the highest AID values, whereas Lys and Thr had the lowest estimates. A similar trend was reported in our previous studies

Table 4. Apparent ileal CP and amino acid (AA) digestibilities for pea protein isolate (PPI), distillers dried grains with solubles derived from a blend of wheat and corn (wcDDGS), and corn samples fed to broilers PPI1 Item CP Indispensable AA  Arg  His  Ile  Leu  Lys  Met  Phe  Thr  Val Dispensable AA  Ala  Asp  Cys  Glu  Gly  Pro  Ser 1Four

wcDDGS2

Range

Mean

85.8 to 94.0

90.6   94.7 92.5 90.7 92.0 94.5 90.8 92.2 86.0 89.1   89.6 91.9 72.6 94.6 88.1 89.2 88.9

89.2 85.5 85.5 87.6 90.9 86.3 87.7 77.8 83.9

to to to to to to to to to

96.8 94.6 93.5 95.0 96.8 95.1 95.0 90.6 93.2

84.2 87.6 58.9 90.3 78.4 83.1 82.7

to to to to to to to

94.0 94.6 82.5 96.9 92.6 91.8 92.9

 

 

                                 

Corn3

Range

Mean

61.2 to 70.1   71.3 to 79.8 60.1 to 73.2 63.8 to 72.2 76.5 to 82.1 44.3 to 59.4 76.7 to 83.1 74.6 to 80.3 56.0 to 63.5 63.3 to 71.5   71.7 to 79.8 50.1 to 61.0 59.5 to 67.2 77.8 to 82.9 55.5 to 64.5 73.5 to 80.8 64.2 to 70.8

65.1   75.4 67.7 68.0 79.8 50.7 79.6 77.2 59.0 67.4   76.1 54.7 62.6 80.2 59.2 77.1 67.2

 

 

                                 

Range

Mean

77.9 to 86.2   92.7 to 99.9 88.8 to 93.7 85.7 to 92.5 92.3 to 95.8 84.1 to 92.0 93.6 to 97.1 88.1 to 93.0 69.8 to 80.0 85.5 to 92.4   90.9 to 95.0 84.6 to 92.2 81.2 to 87.8 91.8 to 96.9 79.5 to 89.3 86.9 to 92.2 82.3 to 89.2

82.1   95.3 90.7 88.4 93.8 87.6 95.2 89.8 73.9 88.1   92.8 87.7 83.5 94.4 83.0 89.7 84.8

different samples of PPI were fed to 144 birds housed in 24 cages (each with 6 birds) to give 6 replicates per sample. different samples of wcDDGS were fed to 180 birds housed in 30 cages (each with 6 birds) to give 6 replicates per sample. 3Five different samples of corn were fed to 180 birds housed in 30 cages (each with 6 birds) to give 6 replicates per sample. 2Five

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with wheat DDGS fed to broilers (Bandegan et al., 2009). However, the AID of AA for wcDDGS used in the current study were generally higher than the AID of AA for wheat DDGS fed to broilers in the study of Bandegan et al. (2009), but lower than the AID of AA for light-colored corn DDGS (similar in color to the one used in the current study) fed to broilers in the study of Adedokun et al. (2008). It should be noted that pentose sugars react more with AA than hexose sugars during Maillard reaction (Rizzi, 2003). Wheat has a higher content of pentose sugars (arabinose and xylose) than corn (Choct, 1997), implying that the impact of high drying temperatures on AA digestibility is higher for wheat DDGS than for corn DDGS. The DGGS used in the current study was derived from a mixture of corn and wheat. Therefore, the higher AA digestibility for corn DDGS used in the study of Adedokun et al. (2008) and lower AA digestibility for wheat DDGS used in the study of Bandegan et al. (2009) compared with AA digestibility of DGGS used in the current study could be attributed to the fact that the DGGS used in the current study was derived from a mixture of corn and wheat. In the current study, Lys had the lowest digestibility in wcDDGS, which was consistent with results of others (Martinez-Amezcua and Parsons, 2007; Bandegan et al., 2009). This implies that Lys is the AA whose

availability is most affected by the process of producing ethanol and its coproducts from cereal grains. Apparent ileal digestibility is a function of bird (as a source of variation) and feed ingredient composition (Ravindran et al., 2005; Huang et al., 2005, 2006; Adedokun et al., 2009). Therefore, variations in feed utilization among birds and variations in nutritional composition among feed samples would contribute to variations in AA digestibilities. Hence, it is as important to report CV associated with digestibility coefficients as it is to report digestibility values. The CV and its components associated with the AID estimates of AA in PPI, wcDDGS, and corn are presented in Table 5. Of the 3 feed ingredients assayed, the CV range was widest for wcDDGS, which could be attributed to the wcDDGS having high fiber content and being subjected to high temperatures during ethanol production. High dietary fiber content can cause variation in feed intake and consequently digestibility of nutrients among birds consuming the same sample, whereas AA availability in feedstuffs can vary with processing temperature. Threonine, Lys, and Arg were the most variable indispensible AA in corn, whereas Lys, His, and Thr were the most variable AA in wcDDGS. Similarly, Thr, Lys, and Arg have been observed to be the most variable indispensible AA in wheat (Bandegan et al., 2011), whereas Lys, His, and Thr have been observed to be the most

Table 5. Coefficient of variation associated with apparent ileal digestibility of CP and amino acid (AA) in broiler chicks fed diets containing pea protein isolate (PPI), distillers dried grains with solubles derived from a blend of wheat and corn (wcDDGS), and corn samples PPI1

wcDDGS2

Variance component CV%4,5

Item CP Indispensable AA  Arg  His  Ile  Leu  Lys  Met  Phe  Thr  Val Dispensable AA  Ala  Asp  Cys  Glu  Gly  Pro  Ser

3.7   4.4 4.1 3.7 3.3 2.7 4.6 3.2 6.1 4.6 5.4 2.9 13.5 2.7 4.8 4.5 4.7

Between samples

Within samples

72.0   62.7 69.9 65.7 69.5 69.5 64.2 66.4 79.1 74.3   73.0 72.1 73.1 70.8 71.9 75.8 82.0

28.0 28.0 37.3 30.1 34.3 30.5 30.5 35.8 33.6 20.9 25.7   27.0 27.9 26.9 29.2 28.1 24.2 18.0

Corn3

Variance component

                                   

CV%

Between samples

Within samples

14.8   12.3 18.4 12.9 7.3 29.4 8.1 8.6 16.7 13.5   9.6 21.1 12.1 6.6 18.6 8.8 12.0

14.5   20.9 24.5 14.3 15.2 24.4 24.0 7.7 8.3 67.4   22.4 14.8 0.0 9.5 13.5 14.8 8.9

85.5   79.1 75.5 85.7 84.8 75.6 76.0 92.3 91.7 32.6   77.6 85.2 100.0 90.5 86.5 85.2 91.1

Variance component

                                     

CV%

Between samples

Within samples

8.6   7.0 5.5 6.3 3.2 7.9 3.0 5.6 10.7 6.5   3.9 6.8 6.7 4.0 9.7 4.5 6.6

41.1   29.2 12.1 41.8 33.5 32.1 26.6 10.6 42.9 35.2   29.9 40.0 44.1 40.7 40.4 44.8 42.9

58.9   70.8 87.9 58.2 66.5 67.9 73.4 89.4 57.1 64.8 70.1 60.0 55.9 59.3 59.6 55.2 57.1

1Four

different samples of PPI were fed to 144 birds housed in 24 cages (each with 6 birds) to give 6 replicates per sample. different samples of wcDDGS were fed to 180 birds housed in 30 cages (each with 6 birds) to give 6 replicates per sample. 3Five different samples of corn were fed to 180 birds housed in 30 cages (each with 6 birds) to give 6 replicates per sample. 2Five

σe2 − σs2

× 100%, where σs2 = variance due to samples; σe2 = variance due to cages within samples; and γ = respective mean of the PPI γ or wcDDGS or corn samples as shown in Table 4. 4Total

CV =

5Percentage

(

)

(

)

contribution to the total variation calculated as σs2 / σs2 + σe2 and σe2 / σs2 + σe2 for samples and cages within samples, respectively.

190

Nandha et al.

variable AA in wheat DDGS (Bandegan et al., 2009). In PPI, Thr, Val, and Arg were the most variable indispensable AA, which is contrary to the results of Bandegan et al. (2011) showing Met, Ile, Leu, and Val to be the most variable indispensable AA in whole peas. Thus, it appears that the process of producing PPI from pea can cause changes in CV associated with AID coefficients of AA for PPI. Variance components of the CV for both wcDDGS and corn showed that withinsample variation (assay condition) was more than between sample variation (feed differences), whereas the reverse was true for PPI. The higher within variation for wcDGGS could have been due to its high fiber content. Similar results have been reported previously by Bandegan et al. (2009) for wheat DDGS fed to broilers. The variability in starch, protein, fiber, and AA content of corn (Song et al., 2004) could have resulted in variation in feed intake by birds, and therefore, greater within sample variation than between sample variation. The presence of antinutritional factors in peas is considered a great contributor to variability observed in the nutritive value of various samples. Therefore, the higher between samples than within-sample variation associated with the AID of each AA in PPI could have been due to the fact that it was devoid of most of the antinutritional factors. It should be noted that in the current study, birds were killed by cervical dislocation, which can result in considerable struggle by the bird as it dies, and hence mixing of digesta between intestinal segments and mucosal shedding. Also, in the current study, ileal digesta was obtained by manually squeezing it out of ileum, which may remove gut lining and mucosa along with digesta as suggested by Poureslami et al. (2012). Thus, the killing of birds by cervical dislocation and the manual squeezing of ileal digest may also have partly contributed to the CV reported in the study. In summary, Thr was the least digestible indispensable AA in PPI and corn, and the second least digestible indispensable AA in wcDDGS (after Lys). Lysine and Arg were the most digestible AA among the indispensable AA in PPI, whereas Arg, Leu, and Met were the most digestible indispensable AA in corn. In wcDDGS, Leu, Met, and Phe were the most digestible indispensable AA. Threonine, Lys, and Arg were the most variable indispensible AA (with regard to the digestibility) in corn, whereas Lys, His, and Thr were the most variable AA in wcDDGS. In PPI, Thr, Met, and Val were most variable indispensable AA. Overall, the CV range for AA digestibility was wider for wcDDGS than for corn or PPI. For wcDDGS and corn, the within-sample variation (assay condition) was more than between-sample variation (feed differences), whereas the reverse was true for PPI.

ACKNOWLEDGMENTS The authors thank Harry Muc (University of Manitoba, Winnipeg, MB, Canada) for his technical assis-

tance. The authors also thank Evonik Industries and the Natural Sciences and Engineering Research Council of Canada (NSERC) for funding this research.

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