Hiroshi Kamisoyama, Kazuhisa Honda and Shin

http://www.jstage.jst.go.jp/browse/jpsa
doi:+*.,+.+/jpsa.*+**./
Copyright ῌ ,*++, Japan Poultry Science Association.
Hiroshi Kamisoyama, Kazuhisa Honda and Shin Hasegawa
Graduate School of Agricultural Science, Kobe University, Kobe 0/1ῌ2/*+, Japan
The present study was conducted to investigate the e#ects of dietary cereals such as corn, sorghum, wheat, hulled barley
and naked barley on amino acid digestibility using fistulized chickens. Chickens were fistulized to either the distal end of the
jejunum, the middle part of the ileum, the distal end of the ileum or the distal end of the rectum. The cereals were
supplemented as the sole source of protein in each experimental diet. Intestinal digesta were collected from each site of the
intestines, and the contents of amino acids were measured. There was no significant di#erence in the true digestibilities of all
measured amino acids between the sites of chicken intestines. However, the true digestibilities of +- amino acids (Asp, Thr,
Ser, Gly, Ala, Val, Met, Ile, Leu, Tyr, Phe, His and Arg) in the hulled barley group, +* amino acids (Asp, Thr, Ser, Gly, Ala,
Val, Met, Ile, Leu and Tyr) in the naked barley group, nine amino acids (Asp, Thr, Gly, Ala, Met, Ile, Leu, Tyr and Arg)
in the wheat group and five amino acids (Gly, Met, Lys, His and Arg) in the sorghum group were lower than those in the
corn group. These results clearly demonstrate that corn shows the highest amino acid digestibility among cereals used in this
study and that there is no significant e#ect of sampling site on the amino acid digestibility of the dietary cereals.
Key words: amino acid digestibility, barley, corn, sorghum, wheat
J. Poult. Sci., .2: +3ῌ,., ,*++
῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍
Introduction
Global demand of corns for feed and fuel will be increasing at a rapid pace in the near future. For example,
meeting the expected demand for meat in emerging economies will require corn usage as a feed ingredient to
increase by about -0 million tons to about /,2 million
tones/year over the next decade (Edgerton, ,**3). During this same period, biofuel production, mainly from
corn, is expected to grow by ,2 billion liters to 01 billion
liters/year (Edgerton, ,**3). Thus, several researchers
have investigated alternatives for corn in feeds for various
livestock species (Nyannor et al., ,**1; Donkin et al.,
,**3; Archimede
◊ et al., ,*+*).
Since the protein requirement of chickens is a requirement for amino acids (NRC, +33.), primary interest has
been placed on the amino acid composition of feed stu#s
for feed formulation. However, more attention has recently been given to the determination of amino acid
digestibility of feedstu#s because not all amino acid in
feedstu#s are equally digested. In addition, amino acid
digestibility has been recognized as a sensitive indicator of
biological availability of protein (Han and Parsons, +33*;
Received: June +., ,*+*, Accepted: September ,., ,*+*
Released Online Advance Publication: November ,/, ,*+*
Correspondence: Dr. S Hasegawa, Graduate School of Agricultural
Science, Kobe University, Kobe 0/1ῌ2/*+, Japan.
(E-mail: [email protected])
Lemme et al., ,**.). Thus, to evaluate the alternatives for
corn, the determination of amino acid digestibility of the
alternatives would be crucial.
To date, there is a large body of published work on
amino acid digestibility coe$cients for di#erent feed ingredients (NRC, +33.). However, the data are variable
due to di#erences in methodology used including the site
of measurement (Ten Doeschate et al., +33-; Kadim and
Moughan, +331; Ravindran et al., +333; Kadim et al.,
,**,; Kluth et al., ,**/; Rezvani et al., ,**2a, ,**2b).
Isshiki et al. (+323) established the progressive method of
intestinal fistulization in chickens for nutritional study.
This method can eliminate the e#ects of gut microflora in
the caecal/colon on the measurement of digestibility and
can be repeated without sacrificing the birds. Using this
method, we previously showed that most of the crude
protein, crude fat and nitrogen-free extract were absorbed
in the proximal part of the ileum when fistulized chickens
were fed formula diets (Kamisoyama et al., ,**3, Honda
et al., ,**3). A similar trend was observed when amino
acid digestibility was measured in the chickens fed the
formula diets (Kamisoyama et al., ,*+*, Honda et al.,
,*+*). There is evidence that the primary site for amino
acid, glucose and fatty acid absorption is the small intestine in birds (Whittow, ,***). Thus, this method is useful
to determine the amino acid digestibility of feed ingredients as alternatives for corn in chickens.
The objective of the present study was to investigate the
Journal of Poultry Science, .2 (+)
20
e#ects of dietary cereals such as corn, sorghum, wheat,
hulled barley and naked barley on amino acid digestibility
using fistulized chickens.
Materials and Methods
Birds and Surgical Procedure for Fistulation
Twenty four ,** day-old male Single Comb White
Leghorn (Ghen Corporation, Gifu, Japan) were used in
this study. The birds were divided into four groups of six
birds each. Each group was fistulized on either the distal
end of the jejunum (DJ, at the position of , cm anterior to
Meckel’s diverticulum), the middle part of the ileum (MI,
at the position of +, cm anterior to ileocecoclonic junction), the distal end of the ileum (DI, at the position of cm anterior to the ileocecoclonic junction) or the distal
end of the rectum (DR, at the position of + cm anterior to
the cloaca) as described previously (Isshiki et al., +323).
All experimental procedures followed the guidelines for
the care and use of experimental animals at the Rokkodai
Campus of Kobe University in Japan.
Postoperative Care
Fistulized birds were placed into individual cages and
fed a commercial diet (CP,+ῌ, ME ,2/ kcal/+** g diet,
Nippon Formula Feed Mfg Co., Ltd. Kanagawa, Japan)
and water ad libitum. Birds that showed a decrease in
body weight were tube-fed +* g of recovery diet (casein
+2.**ῌ, glucose /2.*,ῌ, corn starch +*.**ῌ, cellulose
,.**ῌ, vitamin mixture *.,*ῌ, mineral mixture /.0-ῌ,
choline chloride *.+/ῌ and aluminum silicate +.**ῌ) for
/ days after operation. Postoperative care and observation were the same as described previously (Isshiki et al.,
Table +.
Composition of experimental diets
Ingredients
Yellow corn
Sorghum
Wheat
Hulled barley
Naked barley
Mineral premix+ῌ
Vitamin premix,ῌ
Chromium oxide
Calculated content
Crude protein (ῌ)
Crude fat (ῌ)
Crude fiber (ῌ)
Nitorogen free extract (ῌ)
Metabolizable energy (kcal/g diet)
+ῌ
+323).
Experimental Diets
The diets were mixed at the same time using the same
batch of ingredients. The composition of the experimental
diets is presented in Table +. In all diets, the cereals served
as the sole source of protein in each diet. All cereals were
purchased from JA Nishinihon Kumiai Shiryou Co. (Kobe,
Japan). Chromium oxide was purchased from Wako Pure
Chemical Industries, Ltd. (Osaka Japan). All other chemicals were purchased from Oriental Yeast Co. Ltd. (Tokyo, Japan).
Sample Collection
Birds had free access to the experimental diets (Table +)
and water for a --day adaptation period followed by a -day collection of digesta from each site of intestines.
Digesta were collected at 3:** and +1:** and samples from
each site of intestines were pooled, mixed and dried at
//῍ for .2 hours. All birds were used repeatedly for all
di#erent dietary treatments. As the interval of the dietary
treatment, birds were fed the commercial diet for 1 days.
Chemical Analysis
Amino acid contents in dried digesta and experimental
diets were determined using an amino acids analyzer
(Hitachi 2-/ῌ/*, Hitachi Inc., Tokyo, Japan) by the standard
methods (AOAC, +33/). For the determination of Cr
concentration, diets and digesta were ashed by a wet-ash
digestion with sodium molybdate, sulfuric acid and nitric
acid. Cr concentration was determined at a wavelength of
..* nm (Bolin et al., +3/,).
Apparent digestibility of amino acid was calculated
using the Cr concentration in the diets and digesta at each
Corn
Sorghum
Wheat
(g/+** g diet)
Hulled
barley
Naked
barley
3,41
3,41
3,41
3,41
/40
+4,
*4/
/40
+4,
*4/
/40
+4,
*4/
/40
+4,
*4/
3,41
/40
+4,
*4/
14.
-4/
+40
004/
-4/
24,
-4*
+41
004-4.
++4,
+41
,4,
0/4.
-4+
342
+43
.4+
0-42
,43
34/
+42
+40
0040
,43
Provided the following quantities of microminerals per kilogram of complete diet: Cu, ,/ mg as copper
sulfate; Fe, +,* mg as iron sulfate; I, *.-* mg as potassium iodate; Mn, ,/ mg as manganese sulfate; Se,
*.-* mg as sodium selenite; and Zn, +,/ mg as zinc oxide.
,ῌ
Provided the following quantities of vitamins per kilogram of complete diet: vitamin A, +*,*-, IU as
vitamin A acetate; vitamin D-, 33, IU as D-activated animal sterol; vitamin E, 22 IU as a-tocopherol
acetate; vitamin K-, +./, mg as menadione dimethylpyrimidinol bisulphite; thiamin, +./ mg as thiamine
mononitrate; riboflavin, +* mg; pyridoxine, ..* mg as pyridoxine hydrochloride; vitamin B+,, *.*/ mg;
D-pantothenic acid, ,/ mg as calcium pantothenate; niacin, 0* mg; folic acid, +./ mg; and biotin, *.. mg.
Kamisoyama et al.: Amino Acid Digestibility of Dietary Cereals
Table ,.
Amino acid composition of experimental diets
(ῌ)
Amino
acid
Corn
Sorghum
Wheat
Hulled
barley
Naked
barley
Asp
Thr
Ser
Glu
Pro
Gly
Ala
Val
Met
Ile
Leu
Tyr
Phe
Lys
His
Arg
*4./
*4,0
*4-+4-.
*40*4-.
*4/*4-1
*4+.
*4,.
*422
*4-+
*4-/
*4,*
*4,*4-,
*4.3
*4,0
*4-.
+4/1
*40,
*4,1
*403
*4.*
*4++
*4,2
+4**
*4-,
*4.*
*4+0
*4+3
*4,0
*4/*
*4-*
*4.,4//
*42.
*4.,
*4-/
*4.*4+*
*4-+
*4/2
*4,3
*4.+
*4,3
*4,*4.1
*4/,
*4-*
*4-0
+43+
*42,
*4.*
*4-0
*4..
*4+*4,3
*4//
*4,3
*4.+
*4-+
*4+3
*4.,
*4/3
*4-0
*4.+
,4-*
+4*+
*4.,
*4.+
*4/+
*4++
*4-*40.
*4-,
*4/*
*4-1
*4,*4/,
site of the intestines by using the equation: Apparent
digestibility of amino acid (ῌ)῏+**ῌ([AAD/AAF]῎
[CrF/CrD]῎+**). In this equation, AAD is the amino
acid concentration present in the digesta at each site of the
intestines, AAF is the amino acid concentration in the diet
(Table ,), CrF is the Cr concentration in the diet, and
CrD is the Cr concentration in the digesta at each site of
the intestines. The intestinal digesta contains endogeneous
nitrogen such as digestive enzymes, mucoproteins, desquamated cells, urea, amino acids produced by cell catabolism, serum albumin and micro-organisms (R´
erat, +312).
Therefore, to calculate the true digestibility of amino acid,
the amino acid contents in digesta of chickens fed the
protein free diet (a-corn starch +*.*ῌ, corn oil -.*ῌ,
cellulose -.*ῌ, mineral mix /.*ῌ, vitamin mix +.,ῌ,
b-corn starch 10.1ῌ, chromium oxide (III) *./ῌ) were
subtracted as endogenous amino acid contents from those
of other groups.
Statistical Analysis
All data were expressed as mean῍SEM. Data were
statistically analyzed by a two-way ANOVA on dietary
treatments and sites of digestive tract. Dunnett’s post hoc
test was then performed using the values of the corn group
(Table /) as the control. Significant di#erence was set at
Pῐ*.*/. All statistical analyses were performed using the
commercial package (StatView version /, SAS Institute,
Cary, NC, USA, +332).
Results
As shown in Table -, the total amino acids contents in
digesta tended to increase at the MI (Pῐ*.*2), DI (Pῐ
*.+*) and DR (Pῐ*.-) compared to the DJ when the
chickens fed the protein free diet. These values were used
for calculation of the true digestibilities of amino acids.
Statistical analysis (two-way ANOVA) did not show
21
any significant interaction between dietary cereals and the
sites of the intestines on amino acid digestibility (data not
shown), and hence, only the results of the main e#ects
were presented in Tables . and /. As shown in Table .,
there was no significant di#erence in amino acid digestibility between the sites of intestines. However, there were
significant di#erences in amino acid digestibility between
dietary cereals (Table /). The true digestibilities of +amino acids (Asp, Thr, Ser, Gly, Ala, Val, Met, Ile, Leu,
Tyr, Phe, His and Arg) in the hulled barley group were
significantly lower than those in the corn group (Table /).
In contrast, the true digestibilities of only five amino acids
(Gly, Met, Lys, His and Arg) in the sorghum group were
significantly lower than those in the corn group (Table /).
The true digestibilities of nine amino acids (Asp, Thr, Gly,
Ala, Met, Ile, Leu, Tyr and Arg) in the wheat group and
+* amino acids (Asp, Thr, Ser, Gly, Ala, Val, Met, Ile,
Leu and Tyr) in the naked barley group were significantly
lower than those in the corn group (Table /). In both the
naked barley and the hulled barley groups, the true digestibility of total amino acids was significantly lower than
that in the corn group (Table /).
Discussion
We previously showed that most of the crude protein
(Kamisoyama et al., ,**3, Honda et al., ,**3) and amino
acids (Kamisoyama et al., ,*+*, Honda et al., ,*+*) were
absorbed in the proximal part of the ileum when fistulized
chickens were fed the casein diet. In the present study,
there was no significant di#erence in amino acid digestibility between the sites of chicken intestines. These results
suggest that most of amino acids were absorbed in the
proximal part of the ileum when chickens were fed either
the corn, sorghum, wheat, naked barley or hulled barley
diets.
In the present study, the true digestibilities of Gly, Met,
Lys, His and Arg in the sorghum group were significantly
lower than those in the corn group (Table /). The prolamin storage protein kafirins are the main form of protein
storage bodies in sorghum. The b- and g-kafirins are known
to contain a significant amount of cysteine (Weaver et al.,
+332) forming disulfide bonds in mature grains (Oria et
al., +33/). The formation of disulfide-bound complexes
has been implicated in the reduction of protein digestibility in mature sorghum grain. It is therefore possible that
the significant di#erence in the amino acid digestibility
between the sorghum and the corn group is due to the
kafirins in sorghum. Nyannor et al. (,**1) reported that
apparent total tract digestibility of nitrogen is significantly
lower in chicks fed the sorghum-soybean meal diet than
those fed the corn-soybean meal diet. However, they also
showed that weight gain, feed intake, and feed e$ciency
are not di#erent between the sorghum-soybean meal diet
and the corn-soybean meal diet. Thus, although the true
digestibilities of several amino acids of the sorghum group
are lower than those of the corn group (Table /), sorghum
could be used as a partial substitute for corn in poultry
Journal of Poultry Science, .2 (+)
22
The amount of amino acids at di#erent sites of the digestive tract of
chickens fed a protein free diet
(mg/day)
Table -.
Asp
Thr
Ser
Glu
Pro
Gly
Ala
Val
Met
Ile
Leu
Tyr
Phe
Lys
His
Arg
Total
DJ
MI
DI
DR
/+41-ῌ 14,*
--43.ῌ+*410
,14.+ῌ 243*
/-4.1ῌ /42*
,.432ῌ +4/+
,-41-ῌ 34**
-*42.ῌ ,43+
,/4-*ῌ /42+
.4.,ῌ ,40/
,/4,-ῌ -4-1
-*421ῌ ,4/*
+-41-ῌ 14-+
+0431ῌ 14-,
+-431ῌ .401
+*41.ῌ 14.,
,-412ῌ 241+
.++4+*ῌ3/42,
.04+1ῌ -4.2
.+4-+ῌ -41.
..4./ῌ 14/.
0.4*-ῌ 1402
.04**ῌ .4-+
-+4/.ῌ +413
-+4.-ῌ ,4*1
,1402ῌ+*43+
1421ῌ 2420
,24/-ῌ /42*
./4+-ῌ +4,.
+.431ῌ 043*
,,4/+ῌ .403
++4.*ῌ 04/2420ῌ ,40*
,/4--ῌ .4*0
.314,*ῌ2,4+2
/-4*.ῌ -4-2
-04/-ῌ /43.
-*4*+ῌ 14+,
/+4.2ῌ 14,+
-.41/ῌ +420
-+4.*ῌ ,401
,14//ῌ .4*+
.*4.1ῌ 34++
+*4*2ῌ 04/0
,04-/ῌ /4/3
.*42+ῌ +42*
+.4/,ῌ 140/
+24+3ῌ 2432
+-4/+ῌ 34++
3410ῌ 341,
+2432ῌ +4*.
./14.,ῌ3+41/
004,+ῌ .4,/,4/1ῌ -40/
/*423ῌ 14/3
2*42.ῌ 24./
/.402ῌ 04*.-4,+ῌ 34+2
-14,,ῌ ,4/1
0/4,/ῌ 34/.
++423ῌ /411
.*4*0ῌ 04-3
/0411ῌ *4/1
,.4,.ῌ 04+3
--40/ῌ .4/,
+/41/ῌ -4-+-40-ῌ 04+/
,14,1ῌ -4.2
01.4++ῌ2140.
Data represent the meanῌSEM of 0 birds.
DJ: the distal end of the jejunum, MI: the middle part of the ileum, DI: the distal end of the
ileum, DR: the distal end of the rectum.
Table ..
Comparison of the true digestibilities of amino acids between the sites
of chicken intestines
(ῌ)
Amino
acid
DJ
MI
DI
DR
Asp
Thr
Ser
Glu
Pro
Gly
Ala
Val
Met
Ile
Leu
Tyr
Phe
Lys
His
Arg
Total
2,4*2ῌ0400
1+4/-ῌ142*
2+41-ῌ/4,3
3,403ῌ/410
22403ῌ/43+
134.-ῌ-42,
2+4.3ῌ.4,3
2.410ῌ/4+1
114,2ῌ/4+1
2-4*2ῌ/4,2241.ῌ04*1
224*3ῌ-4.3
2241/ῌ.4.,
1343.ῌ-402
214,,ῌ/4-.
214+.ῌ-4//
2-43,ῌ.4/0
204/1ῌ041,
2*4/*ῌ/4*0
3*403ῌ24.3.410ῌ0423.4*.ῌ.43214**ῌ.431
2/4+*ῌ14/+
3,4+3ῌ-4/0
2+4**ῌ.4.*
224,0ῌ.4*3
3,4*+ῌ,4,1
3+4*2ῌ.41+
3-4-,ῌ04.3
1243,ῌ14*,
2242*ῌ-4*0
3+4.+ῌ04*+
224.2ῌ/4-0
2/4*1ῌ14,2
2-410ῌ-41.
234*-ῌ/412
3-420ῌ-4.3
3,42,ῌ04+0
2+4,*ῌ04+2-42/ῌ/412
20430ῌ/4//
12412ῌ/4-/
2043/ῌ042,
3*4,3ῌ/4/,
234.1ῌ04-*
3*4.*ῌ-413
2*4*/ῌ/4+0
224/3ῌ.4-224/3ῌ-4,/
2042/ῌ-4/.
2,4-*ῌ.42*
13423ῌ04,.
204-0ῌ.4/,
3,41+ῌ.433,41.ῌ.4-.
114*2ῌ.410
2+4-2ῌ-43,
2140*ῌ/4-114-1ῌ.4-2
2/412ῌ.403
234,3ῌ/420
224-/ῌ.4*/
234*-ῌ-42+
1140.ῌ.4*2
204*3ῌ-43*
214**ῌ-4,,
2/4*.ῌ-433
Data represent the meanῌSEM of -* birds.
DJ: the distal end of the jejunum, MI: the middle part of the ileum, DI: the distal end of the
ileum, DR: the distal end of the rectum.
diets.
Beta-glucans present in the endosperm cell walls of
barley is known to be a major cause of the suppression of
growth rate in chicks fed barley diet. This e#ect is attributed to an increase in intestinal viscosity (Burnett, +300;
White et al., +32+). In fact, Almirall et al. (+33/)
reported that dietary b-glucanase decreases intestinal vis-
cosity and increases ileal crude protein digestibility in
chicks fed barley diet. Edney et al. (+323) reported that
dietary b-glucanase was highly e#ective in improving
growth and feed conversion of broiler chicks fed on hulled
barley or hulless barley diets. In the present study, the
true digestibilities of total amino acids in the naked barley
and the hulled barley groups were significantly lower than
Kamisoyama et al.: Amino Acid Digestibility of Dietary Cereals
Table /.
23
Comparison of the true digestibilities of amino acids between dietary cereals
(ῌ)
Amino
acid
Corn
Sorghum
Wheat
Hulled barley
Naked barley
Asp
Thr
Ser
Glu
Pro
Gly
Ala
Val
Met
Ile
Leu
Tyr
Phe
Lys
His
Arg
Total
3.4,0ῌ.42*
3*4--ῌ-413/422ῌ/4+1
314.*ῌ-4+1
3/43-ῌ.4,2
3*4,-ῌ/4*,
3/4+.ῌ/422
3141.ῌ.410
3,41.ῌ-4/0
3/42-ῌ-411
314/3ῌ-43.
304*0ῌ.4+2
3043-ῌ/42,
2.4-*ῌ/4,1
3/4.-ῌ/4+/
3041+ῌ,401
3.4/-ῌ.4/3
214.+ῌ.4.2*40*ῌ/432
2143*ῌ/43.
3-4.-ῌ/41.
214/0ῌ.4-1
134*-ῌ.421*
3+412ῌ/4+.
3*4*2ῌ-40*
2+43+ῌ/432*
224/*ῌ-41,
3-433ῌ/4**
3+4*2ῌ/4,2
3,4+1ῌ,4/1,41*ῌ.4/-*
2-41.ῌ/4*/*
214,0ῌ-4./*
2042,ῌ040+
2,4/.ῌ-40.*
1242*ῌ-41/**
224-*ῌ/41/
3.43*ῌ-4,+
3/4/2ῌ-4*/
2+4+,ῌ,42**
12402ῌ,4-+**
204,*ῌ.4-/
1/4/2ῌ,43/*
20432ῌ-42-*
2342*ῌ,402*
234.*ῌ,4+.**
23430ῌ-423
2+4,*ῌ,4-3
234*/ῌ,4-*
214,/ῌ+4-3**
2/430ῌ.431
1.402ῌ14+1*
004..ῌ/40***
124+1ῌ/4*+*
234-*ῌ/4*,
234/3ῌ/421
1.41/ῌ/4*+*
1+4.2ῌ.423*
1243*ῌ/4/.*
034.,ῌ.4*3*
1/4/.ῌ/4-/*
2-402ῌ.422*
2-4/,ῌ.4.,*
2.41.ῌ/4*3*
1.4//ῌ.43*
2-4-+ῌ,40/*
2.4,0ῌ.400*
12423ῌ,4-/**
2+4+/ῌ142.*
124./ῌ/43/*
2.4/,ῌ.4.-*
3,4/+ῌ/422
3+41+ῌ/42+
2*410ῌ-42/*
1141*ῌ/4--*
204.1ῌ/4,-*
1-4.+ῌ.4/.*
2-4,/ῌ04+.*
2/4-0ῌ/4*3*
204+2ῌ.4,3*
224*1ῌ/43.
2,43-ῌ.410
2042/ῌ-4*0
214,+ῌ/4.*
2.4+0ῌ,4.**
Data represent the meanῌSEM of ,. birds.
*,**: significant with respect to the corn group (P῍*.*/ and *.*+).
those in the corn group (Table /). It is therefore possible
that b-glucans in the barley might be involved in the low
amino acid digestibility in the hulled and naked barley
groups.
The true digestibilities of nine amino acids (Asp, Thr,
Gly, Ala, Met, Ile, Leu, Tyr and Arg) in the wheat group
were significantly lower than those in the corn group
(Table /). As shown in Table +, the crude protein content
of the wheat diet (++.,ῌ) is +./-fold higher than that of
the corn diet (1./ῌ), and the crude fat content of the
wheat diet (+.1ῌ) is lower than that of the corn diet
(-./ῌ). We previously showed that dietary protein levels
(+*ῌ-*ῌ) do not influence the true digestibility of amino
acid at the DR when chickens were fed casein-corn oil diet
(Kamisoyama et al., ,*+*). We also reported that dietary
fat levels (-ῌ+*ῌ) do not influence the true digestibility of
amino acid at the DR when chickens were fed caseintallow diet (Honda et al., ,*+*). It is therefore possible
that the di#erence in the content of crude protein or crude
fat is related to the low amino acid digestibility in the
wheat group (Table /). Further study will be needed to
address this possibility.
Arabinoxylans and b-glucans are major components of
cell walls of mature wheat endosperm. Arabinoxylans
increase the viscosity of wheat-based diets in chickens and
interfere with digestion and absorption of the nutrients
(Annison and Choct, +33+). Since dietary xylanase hydrolyzes the arabinoxylans and releases the enclosed nutrients, chickens can digest the nutrients more easily and
achieve better growth performance (Choct and Annison,
+33,). On the other hand, a dietary b-glucanase is not
e#ective in improving amino acid digestibility in broiler
chicks fed on wheat-soybean meal diet (Edney et al.,
+323). It is therefore possible that arabinoxylans in the
wheat might be involved in the low amino acid digestibility in the wheat group.
In summary, we investigated the true digestibilities of
all amino acids except for tryptophan of dietary cereals at
di#erent sites of chicken intestines. Our results showed
that the true digestibilities of +- amino acids in the hulled
barley group were significantly lower than those in the
corn group. In contrast, the true digestibilities of only five
amino acids in the sorghum group were significantly lower
than those in the corn group. The true digestibilities of
nine amino acids in the wheat group and +* amino acids in
the naked barley group were significantly lower than those
in the corn group. These results clearly demonstrate that
corn shows the highest amino acid digestibility among
cereals used in this study and that there is no significant
e#ect of sampling site on the amino acid digestibility of the
dietary cereals.
Acknowledgments
This work was supported by a Grant-in-Aid (Number
+3,*2*,.) for Scientific Research (A) from the Ministry
of Education, Culture, Sports, Science, and Technology of
Japan.
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