Agriculture Reference
In-Depth Information
300
250
200
150
Lys
Thr
Met
200
50
0
0
0 0 0 0 0 0 0 0
Required AA intake (
LAAI
)
90
100
110
120
130
140
150
Fig. 6.5.
Amino acid requirement curves for juvenile male Nile Tilapia (
Oreochromis niloticus
),
NR
and
LAAI
in terms of mg/BW
k
0.67
/day. (From Liebert, 2009.)
available procedures to derive optimal or ideal
dietary AA ratios (
IAAR
s). Today, most of the
published
IAAR
recommendations are derived
from results of quantitative AA requirement
studies (supplementation technique) or from
supplementation studies in which the opti-
mal ratio of lysine to an individual AA under
study is measured by adding graded levels of
the test AA (Emmert and Baker, 1997). Max-
imal response based on varying criteria is
used to indicate the
IAAR
to lysine as a refer-
ence. Such procedures are widely distributed
for evaluation of ideal/optimal dietary AA ra-
tios, but possess similar disadvantages to the
supplementation technique in general. Con-
sequently, the varying ratio between native
and supplemented AA is a factor of influence
that cannot be easily eliminated. Taking into
account any assumed difference in ileal di-
gestibility is not a sufficient tool.
Generally, according to our procedure,
results from modelling AA requirements can
also be utilized to improve the database about
the
IAAR
s depending on species, age, geno-
type, sex and other factors. Observed require-
ments can be related to lysine needs within
species, genotype, sex and age at equal levels
of desired performance.
In addition, it is also possible to obtain
this information about
IAAR
s directly from
measured
bc
-
1
data. What is the physiological
meaning of the model parameter 'AA effi-
ciency'? In fact, it is a reflection of the quantity
A disadvantage of our approach is that an as-
sessment of dietary AA efficiency is only jus-
tified for the AA in the limiting position.
Compared to the simultaneous measurement
of ileal digestibility for several individual
AAs, this restriction acts really as a disadvan-
tage of the procedure. However, it is a physio-
logical fact of the fundamental 'law of the
minimum' that only the utilizable part of
LAAI
is able to respond in
ND
in the animal.
Otherwise, the physiological meaning of ileal
disappearance rate of individual AAs for feed
evaluation is questionable. In addition, the N
losses from digestive processes of food pro-
ducing animals are much lower as compared
to the metabolic N losses from deficiencies of
post-absorptive utilization processes. When
accounting for these facts the disadvantage is
more apparent. In addition, evaluation of
feed treatment effects on individual AA effi-
ciency, which may include much more than
effects on digestibility only (e.g. heat dam-
aged lysine), needs special methods to reveal
more complex impacts. This is an important
additional field of application for AA
efficiency- based investigations.
Ideal amino acid ratios (IAARs) based
on dietary amino acid efficiency
In the most recent application of the 'Goettin-
gen approach' we started to improve currently
