Agriculture Reference
In-Depth Information
used as an assessment of quality of any dietary
protein based on the AA pattern of a reference
protein considered to be 'ideal'. Thus, know-
ledge of the optimal dietary AA pattern in
broiler diets is continuously being improved
by the use of several procedures with differ-
ent physiological bases and accuracy.
Conventionally EAA requirements have
been assessed by dose-response studies
using the graded supplementation tech-
nique (Baker and Han, 1994; Mack
et al
.,
1999; Baker
et al
., 2002). However, this
method is expensive and time-consuming
(Rollin
et al
., 2003) because multiple assays
are needed. Therefore, another practical
method was developed to measure the com-
position of the EAAs in the ideal protein
required for swine (Fuller
et al
. 1989; Wang
and Fuller, 1989) and this was later adapted
for broilers (Gruber
et al
., 2000; Roth
et al
.,
2001). The AA dilution method relies on
a single experiment to determine optimum
ratios of all EAAs. This method is based
on the concept that the reduction of a non-
limiting AA has no effect on nitrogen (N)
deposition. Thus, the changes in N depos-
ition measured on removal of a proportion
of each EAA in turn are used to calculate a
dietary AA pattern in which all EAAs were
equally limiting. The advantage of this
method is that all AA ratios are determined
simultaneously using the same stock of ani-
mals and the same balanced diet (Green and
Hardy, 2002). Consequently this allows bet-
ter uniformity and consistency, facilitating
the precision needed to determine the opti-
mum AA ratios.
For practical use, Rollin
et al
. (2003)
proposed an equation to determine the AA
requirement that is described by a broken
line regression. Although it was suggested
that the utilization of a limiting EAA is well
described by a non-linear model (Fatufe
et al
., 2004; Samadi and Liebert 2008), the
inflection point of a broken line model can
predict minimal requirement values that are
desirable for calculating EAA ratios (Baker,
2003). This method also assumes that the
efficiencies of the EAAs are similar independ-
ent of their dietary concentration. Actually,
it is known that the efficiency of utilization
of the dietary AA is an important factor
that affects amino acid requirements (Sama-
di and Liebert, 2006, 2007). Considering an
equal protein deposition, the AA require-
ment is only dependent on the efficiency of
its utilization (Samadi and Liebert, 2008). In
this way, it is possible to compare the effi-
ciency of utilization of individual AAs directly
to evaluate the optimal AA ratio (Samadi
and Liebert, 2008). This procedure to derive
a scale of optimal AA ratios within one ex-
periment is still under evaluation.
N deposition can be assessed when using
the dilution method either by the N balance
technique, where deposited N is obtained
from the difference between N intake and
N excretion, or by comparative slaughter,
where deposited N corresponds to the diffe-
rence in body N of broilers between the start
and the end of the experimental period.
However, the undetected and additive losses
of feed and excreta can overestimate N de-
position when using the N balance technique,
and losses from the comparative slaughter
technique can lead to errors in the opposite
direction (Just
et al
., 1982). Studies compar-
ing both techniques indicate that the diffe-
rence between these estimations of nitrogen
deposition is variable (Just
et al
., 1982), but
the description of its influence on the deter-
mination of the EAA pattern has been exam-
ined in only a small number of studies
(Zhengling, 2001).
In this context, the objective of the pre-
sent study was to compare two approaches
using the AA dilution method, comparative
slaughter and the N balance technique, to
re-evaluate the actual assumptions of an ideal
ratio between the EAAs: lysine for male
Cobb 500 broilers over three periods of
growth (
6
to 21 days,
22
to 37 days and
38
to
53 days).
Materials and Methods
One N balance trial was performed per age
period (I:
6
to 21 days, II:
22
to 37 days and
III:
38
to 53 days) using male Cobb 500
broilers. The experimental design consisted
of
12
experimental diets and ten replicates
per treatment. This study included two
approaches for determining the optimum
