Agriculture Reference
In-Depth Information
of AA needed to yield one unit of
ND
in the
animal. This quantity depends on the con-
tent of the test AA in the body protein being
synthesized. Moreover, it also indicates in-
directly how the individual AA is involved
in metabolic processes other than protein
synthesis for protein deposition. Conse-
quently, processes of body protein turnover
are reflected by the level of
bc
-
1
,
but only as
an undefined part of the 'black box' protein
utilization. Finally, those physiological pro-
cesses within the black box animal are part
of the recommended requirement, but are
not known in quantitative detail.
As a consequence, the slope relating
dietary concentration of the
LAA
and the
achieved
ND
(as described by model param-
eter
b
, independent of
NI
) is AA-specific
too, according to individual AA functions
and varying needs for synthesis of body
protein. Additionally, this slope is also in-
fluenced by varying AA bioavailability in
the ingredients used in the test diet. The lat-
ter factor is mostly in focus when the diet-
ary efficiency of an AA is evaluated both for
feed quality studies and for modelling AA
requirements with graded dietary AA effi-
The question arises as to whether AA
efficiency data are directly useful for deriv-
ing
IAAR
s from observed individual AA ef-
ficiency data. According to the first of our
reports dealing with this application (Lie-
bert, 2008; Samadi and Liebert, 2008) Eqn 6.8
defines the
IAAR
as derived from observed
AA efficiency data making use of lysine as
the reference AA:
IAAR
=
bc
Lys
-
1
:
bc
LAA
-
1
Table 6.7.
Summarized optimal dietary AA ratios
for growing chickens as derived from meta-analysis.
(From Wecke and Liebert, 2013.)
Optimal dietary ratios for
individual AA as related to Lys
n
Average
Standard deviation
Lysine
26
100
0
Methionine
22
40
4
Methionine +
cysteine
24
74
2
Threonine
24
66
3
Tryptophan
22
16
1
Arginine
25
105
4
Histidine
12
34
4
Isoleucine
24
69
4
Valine
21
80
4
Leucine
12
110
6
Phenylalanine
8
66
3
Phenylalanine +
tyrosine
9
120
7
is possible, the whole AA-balanced com-
plete diet needs to be diluted with starch,
and then refilled with crystalline AAs up to
the former level of the balanced AA supply,
except for the AA under study, which has to
remain in the limiting position. In principle,
the procedure has been described previously
(Fisher and Morris, 1970; Gous and Morris,
1985; Wang and Fuller, 1989; Baker, 2003).
A brief summary of current data from these
experiments is shown in
Table 6.8
. Details
of the diet construction and AA composition
are given in the full papers (Pastor
et al
., 2013;
Wecke and Liebert, 2013).
It has to be noted that the derived
IAAR
s
according to Eqn 6.8 are also a reflection of
the measured AA efficiencies typical of the
composition of the basal diet used to create
the AA-balanced control diet as the starting
point for further individual AA deletions.
Consequently, it cannot be expected that the
observed
IAAR
s will be constant, due to the
dependency of AA efficiency on both AA
absorption and post-absorptive utilization.
However, if the assumptions about the
reference
IAAR
s from meta-analysis are
valid, the deletion of added single crystal-
line AA from the refilled balanced control
diet should yield a significant decline in
dietary protein quality (
b
). Consequently,
(6.8)
However, this application needs individ-
ual AA efficiency data to be provided by
diet dilution. The first step is to develop an
AA-balanced control diet that may be used
for further individual AA dilution.
Table 6.7
summarizes the results of a meta-analysis
about
IAAR
s for growing chickens, which
was basically utilized to create such an
AA-balanced control diet (Wecke and
Liebert, 2013) using crystalline AA supple-
mentation.
In addition, before an individual AA
deletion and measurement of AA efficiency
