Download Ileal endogenous amino acid flow response to nitrogen

Ileal endogenous amino acid flow response to nitrogen-free diets
with differing ratios of corn starch to dextrose in broiler chickens
C. Kong and O. Adeola1
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2054
ABSTRACT An experiment was conducted to determine response in digestibility of DM and the AA composition of ileal endogenous flow of 26-d-old broilers
to nitrogen-free diets (NFD) formulated with different
ratios of corn starch to dextrose. A total of four hundred eighty 3-wk-old broiler chickens were used in a 4-d
trial to estimate ileal endogenous flow (IEF) of amino
acid (AA). The ratios of dextrose to corn starch investigated were 0:849, 283:566, 566:283, or 849:0 for diet
numbers 1, 2, 3, or 4, respectively. All diets contained
a calculated dietary electrolyte balance of 115 mEq/kg
and chromic oxide (5 g/kg) as an indigestible marker.
The birds received a standard starter diet from d 1 to
22 posthatch. On d 22 posthatch, all the birds were
weighed and allocated to 4 treatments in a randomized
complete block design. On d 26 posthatch, birds were
asphyxiated with CO2 and ileal digesta was collected.
Ileal DM digestibility was lowest in diet 1 (77.9%) and
increased as the proportion of corn starch in the diet
decreased. The IEF for all the indispensable AA were
different (P < 0.01) among diets with the exception of
Thr, which was not (P = 0.07). The respective IEF of
AA (mg/kg of DMI) in birds fed diets 1, 2, 3, or 4 were
630, 664, 646, or 1,235 for Lys, 173, 172, 177, or 361 for
Met, and 68, 74, 70, or 166 for Trp. For the dispensable
AA and total AA, IEF of most AA except for Cys and
Pro was highest (P < 0.01) in diet 4. Ileal endogenous
flow of Pro was not different among diets. Diet 4 had
the lowest (P < 0.01) IEF of Cys, whereas there was
no difference among other diets. In conclusion, the data
from the current study show that the variation in proportion of corn starch and dextrose in a nitrogen-free
diet may affect estimates of ileal endogenous flows of
N and AA.
Key words: amino acid, broiler chicken, digestibility, endogenous amino acid flow, nitrogen-free diet
2013 Poultry Science 92:1276–1282
http://dx.doi.org/10.3382/ps.2012-02835
INTRODUCTION
It is well known that the majority of amino acid
(AA) absorption takes place in the small intestine rather than the hindgut, where significant microbe-induced
alteration of AA composition occurs by microorganisms
(Ravindran et al., 1999). Therefore, ileal digestible AA
is preferred for formulating poultry diets.
Extensive research has been conducted to estimate
apparent ileal AA digestibility in poultry (Ravindran
et al., 2005; Kong and Adeola, 2010), but apparent ileal digestibility does not account for endogenous AA
contribution to ileal digesta and consequently leads
to underestimation of AA digestibility in low-protein
ingredients (Stein et al., 2007). There are several approaches available to correct for endogenous amino acid
losses in poultry including feeding of the nitrogen-free
diet (NFD, Furuya and Kaji, 1989), the regression
©2013 Poultry Science Association Inc.
Received October 9, 2012.
Accepted January 24, 2013.
1 Corresponding author: [email protected]
method (Kluth and Rodehutscord, 2009), the peptide
alimentation (enzyme hydrolyzed casein) method (Ravindran and Hendriks, 2004), and feeding of highly digestible protein (HDP, Adedokun et al., 2008). Each of
these methods has some advantages and disadvantages.
Among methods, feeding of NFD may be the preferred
method due to its simplicity in methodology, even
though this method suffers from disadvantages such
as nonphysiological feeding and underestimation of endogenous losses of amino acids (Donkoh and Moughan,
1999; Stein et al., 2007). For pig study, Jansman et al.
(2002) concluded that estimates of basal endogenous
AA in pigs fed NFD are similar or only slightly lower
compared with values from either feeding HDP or the
regression method. This conclusion might be extended
to broilers, and indeed, Adedokun et al. (2007c, 2008)
found that standardized ileal AA digestibility corrected
by NFD or HDP method did not differ for most plant
feedstuffs, even though endogenous losses derived from
NFD method were slightly lower compared with values
from the HDP method.
Nitrogen-free diets have been commonly formulated
with corn starch and dextrose or sucrose as major in-
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ENDOGENOUS AMINO ACID FLOW IN BROILERS
gredients (approximately 85% of NFD), and corn starch
to dextrose or sucrose ratio varies (7:1 to 1:7) in poultry studies (Adedokun et al., 2007c, 2008; Golian et
al., 2008). Even though basal endogenous losses of AA
are theoretically independent of dietary composition,
there is still concern about the influence of ingredient
composition of NFD for animals in terms of its estimation. Because of this, Stein et al. (2007) suggested a
standard NFD diet to estimate basal endogenous AA
losses in pigs. However, there is a scarcity of data on
the variation in AA composition of basal endogenous
losses in broiler chickens fed NFD of varying ingredient
composition. Thus, the objective of the current study
was to determine the response in digestibility of DM
and the AA composition of ileal endogenous flow of
26-d-old broilers fed NFD formulated with different ratios of corn starch to dextrose.
MATERIALS AND METHODS
Broilers
A total of five hundred thirty 1-d-old male Ross 708
broiler chickens were tagged, weighed as a group, and
assigned to cages. All birds received standard broiler
starter diet for 21 d from d 1 to 22 posthatch. The regular starter diet was formulated to contain the following
per kilogram: 3,143 kcal of ME, 226 g of CP, 10 g of Ca,
7.2 g of P, 4.7 g of nonphytate P, 14.3 g of total Lys,
and 8.3 g of total Met. On d 22, four hundred eighty
birds were weighed individually, grouped into 12 blocks
by BW, and randomly allocated to 4 dietary groups in
each block with 10 birds/cage in a randomized complete block design using the Experimental Animal Allotment Program of Kim and Lindemann (2007).
Diets
Ingredient composition of the diets is shown in Table
1. The experimental diets consisted of 4 NFD and the
ratio of dextrose to corn starch investigated in the NFD
were 0:849, 283:566, 566:283, or 849:0 for diet numbers
1, 2, 3, or 4, respectively. All diets contained calculated
dietary electrolyte balance of 115 mEq/kg, and SolkaFloc, soybean oil, monocalcium phosphate, MgO, and
limestone at 50, 35, 22, 0.9, and 17 g/kg, respectively.
Vitamin-mineral premix was supplemented according
to NRC (1994) requirements, and chromic oxide was incorporated into diets (5 g/kg) as an indigestible marker.
Management
Broilers were housed in electrically heated battery
cages (model #SB 4 T, Alternative Design Manufacturing, Siloam Spring, AR) in an environmentally controlled room. Battery temperature on d 1 to 8, 8 to 15,
Table 1. Ingredient composition of the experimental diets
Dietary treatment number
Item
Corn starch:dextrose
Ingredient, g/kg
Corn starch
Dextrose
Solka-Floc1
Soybean oil
Monocalcium phosphate
Limestone
Sodium bicarbonate
Potassium chloride
Magnesium oxide
Potassium carbonate
Choline chloride
Vitamin-mineral premix2
Chromic oxide premix3
Total
Calculated nutrient and energy
Protein, g/kg
TME, kcal/kg
Ca, g/kg
nPP,4 g/kg
Electrolyte balance,5 mEq
1Purified
1
2
3
4
849:0
 
849.1
0.0
30
35
22
17
7.5
3
0.9
3
2.5
5
25
1,000
 
0
3,870
9.98
4.62
114.8
566:283
 
566.1
283.0
30
35
22
17
7.5
3
0.9
3
2.5
5
25
1,000
 
0
3,774
9.98
4.62
114.8
283:566
 
283.0
566.1
30
35
22
17
7.5
3
0.9
3
2.5
5
25
1,000
 
0
3,678
9.98
4.62
114.8
0:849
 
0.0
849.1
30
35
22
17
7.5
3
0.9
3
2.5
5
25
1,000
 
0
3,581
9.98
4.62
114.8
cellulose (International Fiber Corp., North Tonawanda, NY).
the following per kilogram of diet: vitamin A, 5,484 IU; vitamin D3, 2,643 IU; vitamin E, 11 IU;
menadione sodium bisulfite, 4.38 mg; riboflavin, 5.49 mg; d-pantothenic acid, 11 mg; niacin, 44.1 mg; choline chloride, 771 mg; vitamin B12, 13.2 µg; biotin, 55.2 µg; thiamine mononitrate, 2.2 mg; folic acid, 990 µg; pyridoxine
hydrochloride, 3.3 mg; I, 1.11 mg; Mn, 66.06 mg; Cu, 4.44 mg; Fe, 44.1 mg; Zn, 44.1 mg; Se, 300 µg.
3Prepared as 1 g of chromic oxide added to 4 g of Solka-Floc.
4nPP = nonphytate phosphorus.
5Calculated as K + Na – Cl in mEq.
2Supplied
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Kong and Adeola
and 15 to 26 were maintained at 35, 32, and 27°C, respectively. Birds were provided ad libitum access to water and experimental diets from d 22 to 26. On d 26, all
of the birds were euthanized by CO2 asphyxiation and
ileal digesta was collected from the distal two-thirds
section of ileum (portion of the small intestine from
Meckel’s diverticulum to approximately 1 cm anterior
to the ileo-cecal junction) by flushing with distilled water. Collected ileal samples from 10 birds within a cage
were pooled and stored in a freezer at −20°C for further
analyses of Cr, N, and AA. All protocols used in the
study were approved by the Purdue University Animal
Care and Use Committee.
Chemical Analysis
At the completion of the experiment, diet samples
were ground to pass through 0.5-mm screen using a
mill grinder (Retsch ZM 100, GmbH & Co. K.C., Haan,
Germany) and freeze-dried ileal digesta samples were
ground using a coffee grinder. Dietary and ileal digesta samples were analyzed for AA, Cr, and DM at the
University of Missouri Experiment Station Chemical
Laboratory [method 982.30 E (a, b, c), AOAC, 2006].
Duplicate proximate analyses were performed on diets
and ileal digesta samples. Dry matter analysis of samples was performed by drying the samples in a drying
oven at 105°C for 24 h (method 934.01, AOAC, 2006).
Chromium concentration in the diets and ileal samples
was determined using the method of Fenton and Fenton (1979). Nitrogen was determined using combustion
method (model FP2000, Leco Corp., St. Joseph, MI),
using EDTA as a calibration standard. Samples for AA
analysis were prepared using a 24-h hydrolysis in 6 N
hydrochloric acid at 110°C under an atmosphere of nitrogen. For Met and Cys, performic acid oxidation was
done before acid hydrolysis. Samples for Trp analysis
were hydrolyzed using barium hydroxide. Amino acids
in hydrolyzates were determined by cation-exchange
chromatography coupled with postcolumn ninhydrin
derivatization.
Calculations
Apparent ileal digestibility (AID) of DM and ileal
endogenous N and AA flow (IEF, mg/kg of DM intake)
in broiler chickens was
AID (%) = [1 − (Cri /Cro ) × (N o /N i )] × 100;
IEF (mg/kg of DMI) = (Cri /Cro ) × ( N o ),
where Cri is the concentration of chromium in the diet
in grams per kilogram of DMI; Cro is the concentration
of chromium in the ileal digesta in grams per kilogram
of DM output; No is the concentration of DM, N, or AA
in the ileal digesta in mg/kg of DM; Ni is the concentration of DM, N, or AA in the diet in milligrams per
kilogram of DM.
Statistical Analysis
Apparent ileal DM digestibility and IEF of N and
AA in broilers fed NFD formulated with different proportion of corn starch and dextrose were compared by
using the GLM procedure of SAS Institute Inc. (2006).
Level of significance was set at 5% and when a significant effect was indicated, treatment means were separated using Tukey’s test.
RESULTS
The analyzed N, AA, and crude fiber contents of the
4 diets and ingredients used in the current study are
presented in Table 2. The analyzed N contents in the
diet 1, 2, 3, 4, corn starch, and dextrose were 0.8, 0.6,
0.4, 0.3, 0.8, and 0.3 g/kg, respectively. The analyzed
individual AA contents in the 4 experimental NFD
were less than 0.4 g/kg of diet and crude fiber contents
ranged between 3.4 and 3.6%.
Apparent ileal DM digestibility and basal endogenous
N and AA losses of broilers fed NFD with different proportion of corn starch and dextrose are shown in Table
3. Apparent ileal DM digestibility was lowest in diet 1
(77.9%, P < 0.01) and increased as the proportion of
corn starch in the diet decreased.
Ileal endogenous N flow was highest (P < 0.01) in
diet 4 (3,169 mg/kg of DMI), but there were no significant differences among other diets. The IEF for all the
indispensable AA were different (P < 0.01) among diets
with the exception of Thr, which was not (P = 0.07).
The respective IEF of AA (mg/kg of DMI) in birds fed
diets 1, 2, 3, or 4 were 630, 664, 646, or 1,235 for Lys,
173, 172, 177, or 361 for Met, and 68, 74, 70, or 166 for
Trp. For the dispensable AA and total AA, IEF of most
AA except for Cys and Pro was highest (P < 0.01) in
diet number 4. Ileal endogenous flow of Pro was not
different among diets (P = 0.15). Diet 4 had the lowest
(P < 0.01) IEF of Cys, whereas there was no significant
difference among other diets.
Table 4 shows the ratio of individual AA to lysine
in IEF of broilers fed NFD with different proportions
of corn starch and dextrose. Tryptophan (0.11 to 0.13)
and Glu (2.12 to 1.73) are the least and the most abundant AA in IEF for all the dietary treatments, respectively.
DISCUSSION
Because of the existing limitations for AID and TID,
which include lack of additivity and a need to represent
specific endogenous losses, respectively, there has been
a growing consensus that standardized ileal AA digestibility is more reliable data for estimating available
AA contents in feed ingredients and diets for poultry
(Lemme et al., 2004). However, it should be noted that
values for SID are affected by the estimates of basal
endogenous losses, which is not dependent on composition of diet but dependent on feed intake. Depending
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ENDOGENOUS AMINO ACID FLOW IN BROILERS
Table 2. Analyzed amino acids, CP, and fiber composition of the experimental diets and ingredients (as-fed basis)
Dietary treatment
Item
Corn starch:dextrose
N, g/kg
Crude fiber, %
Indispensable amino acid, g/kg
Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Trp
Val
Dispensable amino acid, g/kg
Ala
Asp
Cys
Glu
Gly
Pro
Ser
Tyr
Total AA, g/kg
Ingredient
1
2
3
4
849:0
0.8
3.6
566:283
0.6
3.6
 
0.1
0.0
0.1
0.3
0.1
0.0
0.1
0.1
0.0
0.1
 
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.1
2.7
283:566
0.4
3.4
 
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.1
 
0.1
0.1
0.1
0.1
0.1
0.1
0.0
0.0
1.5
0:849
0.3
3.5
 
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
 
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.8
0.1
0.1
0.1
0.4
0.1
0.1
0.2
0.1
0.0
0.2
0.2
0.2
0.2
0.1
0.1
0.2
0.1
0.1
3.5
on dietary AA intake, the relative importance of basal
endogenous losses on total ileal flows varies and is most
pronounced when dietary AA intake is low, indicating magnification of difference in digestibility possibly
caused by variation of basal endogenous losses. There-
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Corn starch
Dextrose
0.8
1.2
 
0.1
0.0
0.1
0.3
0.1
0.1
0.2
0.1
0.0
0.2
 
0.2
0.2
0.1
0.1
0.1
0.2
0.1
0.1
2.6
0.3
1.7
 
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
 
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.2
fore, there has been a demand to measure the basal
endogenous AA losses correctly, and several methods
have been suggested (Lemme et al., 2004; Ravindran et
al., 2004). Among methodologies, due to the simplicity, the NFD feeding method has been widely used to
Table 3. Ileal DM digestibility and ileal endogenous N and amino acid flow of broilers fed N-free diets with different proportions of
corn starch and dextrose
Dietary treatment
Item
1
Corn starch:dextrose
Ileal digestibility, %
DM
Ileal endogenous flow, mg/kg of DMI
N
Indispensable amino acid
Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Trp
Val
Dispensable amino acid
Ala
Asp
Cys
Glu
Gly
Pro
Ser
Tyr
Total AA
n1
849:0
a–cWithin
1Number
77.9c
2
3
566:283
283:566
82.9b
86.3a
4
 
SEM
P-value
0:849  
88.0a
 
0.87
<0.01
2,075b
2,212b
2,055b
3,169a
 
201
<0.01
575b
248b
541b
875b
630b
173b
500b
804
68b
660b
598b
256b
556b
893b
664b
172b
523b
772
74b
674b
586b
248b
533b
876b
646b
177b
511b
728
70b
648b
1,019a
415a
855a
1,450a
1,235a
361a
826a
966
166a
1,013a
 
 
 
 
 
 
 
 
 
 
77
28
60
103
93
22
56
65
11
72
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
0.070
<0.01
<0.01
572b
1,015b
1,085a
1,337b
653b
675
711b
390b
12,779b
12
572b
1,063b
944a
1,362b
666b
655
708b
402b
12,692b
12
550b
1,023b
871a
1,314b
627b
628
680b
395b
12,109b
12
905a
1,637a
549b
2,131a
949a
830
1,026a
637a
17,544a
12
 
 
 
 
 
 
 
 
 
 
63
110
78
146
63
66
73
39
1,172
 
<0.01
<0.01
<0.01
<0.01
<0.01
0.150
<0.01
<0.01
<0.01
 
a row, means without a common superscript differ.
of replicate cages with 10 birds per cage.
1280
Kong and Adeola
Table 4. Ratio of individual amino acid to lysine in ileal endogenous flow of broilers fed N-free diets with different proportions of
corn starch and dextrose
Published data1
Current data
Item
Corn starch:dextrose
Age, d
Indispensable amino acid
Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Trp
Val
Dispensable amino acid
Ala
Asp
Cys
Glu
Gly
Pro
Ser
Tyr
1Ratios
1
2
849:0
566:283
26
3
4
283:566
0:849
 
 
0.91
0.39
0.86
1.39
1.00
0.27
0.79
1.28
0.11
1.05
0.90
0.39
0.84
1.34
1.00
0.26
0.79
1.16
0.11
1.02
0.91
0.38
0.83
1.35
1.00
0.27
0.79
1.13
0.11
1.00
0.83
0.34
0.69
1.17
1.00
0.29
0.67
0.78
0.13
0.82
 
 
 
 
 
 
 
 
 
 
0.91
1.61
1.72
2.12
1.04
1.07
1.13
0.62
0.86
1.60
1.42
2.05
1.00
0.99
1.07
0.61
0.85
1.58
1.35
2.04
0.97
0.97
1.05
0.61
0.73
1.33
0.44
1.73
0.77
0.67
0.83
0.52
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Adedokun et al.,
2007a
Golian et al.,
2008
Ravindran et al.,
2004
169:640
21
 
0.93
0.40
0.90
1.39
1.00
0.28
0.85
1.51
NA3
1.18
762:802
21
 
1.33
0.53
1.16
1.72
1.00
0.38
2.43
2.51
0.41
1.56
0:819
35
 
1.34
0.76
1.37
2.10
1.00
0.48
1.37
2.45
0.45
2.00
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
calculated as basal endogenous losses of individual amino acid divided by respective Lys loss.
2Sucrose.
3Not
available.
estimate basal endogenous AA losses in poultry, and
corn starch and dextrose are commonly used as major
ingredients to formulate NFD (approximately 85% of
NFD). However, the ratio of corn starch to dextrose
or sucrose varies (7:1 to 1:7) in several poultry studies
(Adedokun et al., 2007c, 2008; Golian et al., 2008). The
variability in formulation of NFD may influence the estimation of the basal endogenous AA losses (Adedokun
et al., 2011) and consequently the estimation of AA digestibility. The results obtained from current 4-d study
showed that the variation in proportion of corn starch
and dextrose in the experimental diet affected endogenous AA flow at the terminal ileum of 26-d-old broiler
chickens, but primarily only when the diet contained no
cornstarch and only dextrose.
In the current study, analyzed individual AA contents of 4 NFD used ranged 0 to 0.4 g/kg, which were
very low and close to the formulated value at 0 g/kg.
Because of the residue from starch production, the
source of AA in the NFD is mainly corn starch, which
is confirmed by the analyzed AA composition of the
corn starch and dextrose that were used in this study.
Results from current study showed that apparent ileal DM digestibility increased from 77.9 to 88.0% as
the proportion of corn starch in NFD decreased from
849.1 to 0 g/kg. This might be, in part, related to the
difference in chemical structure between corn starch
and dextrose. Starch is a polysaccharide consisting of
a large number of glucose units joined by glycosidic
bonds, whereas dextrose is a simple monosaccharide as
the D form of glucose. Because 2 main components of
starch are amylose and amylopectin, which are interconnected by an α-1, 6 linkage (Moran, 1982), they
would be digested into small molecules before absorption but dextrose can be rapidly absorbed without any
enzyme assimilation. In addition, we observed that
the amount of ileal digesta collected decreased as corn
starch amount in the diet decreased as supported by
DM digestibility. Thus, it could be hypothesized that
the difference in the chemical structure and the digestion and absorption process of major energy sources
(corn starch and dextrose) in NFD is responsible for
the differences in the ileal DM digestibility of broilers fed NFD formulated with a different corn starch to
dextrose ratio.
Ileal endogenous flow of N and all AA except for Thr,
Cys, and Pro was highest (P < 0.01) in diet 4 with a
dextrose to corn starch ratio of 849:0. Ileal endogenous
flow of Thr and Pro was not different among diets. Diet
4 has the lowest (P < 0.01) IEF of Cys, whereas there
was no difference among other diets. It could be speculated that the obtained results in the current study
may be, in part, attributed to the inefficient digestive
enzyme reutilization by the birds. Digestive enzymes
are one of the sources of endogenous proteins and excess digestive enzyme might be reused as either a component of other endogenous proteins after degradation
and absorption or a recycled enzyme after the conservation process (Rothman et al., 2002). Because diet 4 did
not have any starch to be digested, secreted pancreatic
α-amylase might not be used in digestion and therefore
not reused by the aforementioned processes otherwise
ENDOGENOUS AMINO ACID FLOW IN BROILERS
excreted and would thus account for endogenous AA
losses. In addition, higher DM digestibility in diet 4
might affect ileal endogenous flow in concert with the
inefficient digestive enzyme reutilization. Undigested
dietary DM could dilute AA in ileal digesta and consequently lower IEF. However, it remains unclear why
diet 4 produced the lowest ileal endogenous Cys loss.
Glutamic acid was the most abundant AA in the IEF
followed by Asp and Thr, which is in agreement with
those reported with 21-d-old broilers fed NFD (Adedokun et al., 2007a,b; Golian et al., 2008). Those abundant AA together accounted for 18.4, 19.1, 19.2, and
21.5% of the total AA flows for diets 1, 2, 3, and 4,
respectively, and these values were very close to the results from our previous study (Kong and Adeola, 2012)
in which corresponding proportion was 20.2% for broilers. Because endogenous AA losses originate from several sources, including salivary and digestive secretion,
epithelial cell turnover as well as mucin secretion in
the gut (Nyachoti et al., 1997; Ravindran and Bryden,
1999), the AA composition of the IEF would be dependent on the AA composition of these sources. Muus
(1954) determined that Glu and Asp were abundant
in the human α-amylase, and Stilborn et al. (2010)
showed that Glu was the most abundant AA in the
feather-free whole chicken body. In addition, mucins accounted for approximately 11% of endogenous protein
in ileal digesta of pigs with Thr contributing 30% to
mucin protein (Lien et al., 1997).
The ileal endogenous AA flow of broilers with the
using of NFD feeding method has been reported by
several researchers (Adedokun et al., 2007a,b; Golian
et al., 2008). In those studies, the ileal endogenous total AA flow varied from 3,935 to 4,368 mg/kg of DMI,
which are lower relative to flows obtained in the current study. This difference may be, in part, due to differences in dietary electrolyte balance. The calculated
electrolyte balance of 115 mEq for 4 NFD used in the
current study is lower than the values calculated in
the above studies (217 to 250 mEq). Because of water consumption, Adedokun et al. (2011) suggested an
electrolyte balance of 108 mEq for NFD. As discussed
by Adedokun et al. (2011), an attempt to meet requirement of electrolyte balance of 250 mEq resulted in high
water consumption due to high Na+ concentration of
NFD (over 0.5%) relative to the requirement (0.2%).
This high water consumption and resultant watery ileal
digesta and excreta might affect the ileal endogenous
flow. Furthermore, neither high water consumption nor
watery excreta were observed in the current study.
Basal endogenous AA losses have been considered one
of primary components of the maintenance AA requirement and due to predominant proportion of mucin protein in these losses, it should more reflect Thr requirement than other components such as basal turnover of
body protein and integumental losses (Moughan, 1999).
In the current study, the Leu in relation to Lys in the
IEF was the highest indispensable AA followed by Thr
except for diet 4. Data from published literature also
1281
showed that relatively higher Thr in relation to Lys in
IEF compared with other indispensable AA (Ravindran
et al., 2004; Adedokun et al., 2007a; Golian et al., 2008).
Moreover, it is interesting to note that indispensable
AA profile in relation to Lys in the IEF determined
with diets 1 to 3 in the current study was fairly comparable (average CV < 4.1) to the respective ratios determined previously in the same laboratory (Adedokun
et al., 2007a), whereas there were inconsistent results
between laboratories (Ravindran et al., 2004; Golian
et al., 2008), which might be as a result of differences
in methodology. These results indicated that the AA
composition in relation to Lys in IEF might be stable
across studies if methodology for IEF remains similar.
The variation in basal endogenous AA losses between
and within laboratories likely resulted from differences
associated with feed ingredients, diet composition and
mixing, and sampling and processing methods as well
as analytical methods (Adedokun et al., 2011). Results
from current study also confirmed the difference in the
IEF of AA caused by the variation of ingredient composition in NFD within the same laboratory. As discussed
above, the impact of variation in IEF observed in the
current study could vary. For example, the respective
variation for Lys between diet 4 and average of other 3
diets was 588 mg/kg of DMI (1,637 vs. 1,049 mg/kg of
DMI) and this difference would change the SID of Lys
for SBM (2.96% Lys; 88.4% DM, NRC, 1994) and corn
(0.26% Lys; 88% DM, NRC, 1994) by 1.76 and 19.93%,
respectively. However, Adedokun et al., (2007a) showed
that the variation in estimates of basal endogenous
could be controlled when a standard protocol, including feeding, sampling, and sample processing, was used
for the estimation across studies. In terms of standard
NFD, it still remains unclear which diet in the current
study should be used for estimating the representative
basal endogenous AA losses of broilers. But it would be
still worth having standard NFD to minimize any possible variation in IEF of AA between studies until more
information become available (Adedokun et al., 2011).
The current study showed that the composition of
energy sources in a NFD may affect estimates of IEF of
N and AA as well as apparent ileal DM digestibility of
broilers fed NFD formulated with different proportions
of corn starch and dextrose in the diets. Therefore, it
would be necessary to use a standard NFD for estimating the IEF of broilers to minimize any variation from
using different NFD across experiments.
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