Agriculture Reference
In-Depth Information
Nitrogen maintenance requirement (
NMR
)
and maximum of theoretical potential
for nitrogen deposition (
ND
max
T
)
Where
LAAI
is the daily intake of the limit-
ing amino acid (mg/BW
k
0.67
) needed for the
intended response level (
NR
); and
bc
-
1
is the
linear slope resulting from the regression of
the concentration of the
LAA
(
c
= g amino
acid/
100
g CP) in the feed protein on protein
quality
b
. The
bc
-
1
considered was in the
linear range, where in each trial an amino
acid was limiting. The conversion factor for
NI
based on the amino acid is given by the
equation
NI
=
16
LAAI
/
c
.
NMR
(mg/BW
k
0.67
/day) was estimated by fit-
ting an exponential function of
NI
and
NEX
(
NEX
=
NMR
·e
b·NI
).
NMR
is the result of an ex-
trapolation when the
NI
is equal to zero; e is
the basic number of the natural logarithm;
and
b
is the equation parameter that repre-
sents the slope of the exponential function. Ni-
trogen retention (
NR
, mg/BW
k
0.67
/day) is the
sum of
ND
and
NMR
, and the theoretical max-
imum for daily nitrogen retention (
NR
max
T
,
mg/BW
k
0.67
/day) is the threshold value of the
exponential function between
NI
and
ND
, i.e.:
NR
=
NR
max
T
× (
1
- e
-
b
×
NI
)
Amino acid requirements
NR
max
T
is the theoretical maximum or poten-
tial for nitrogen retention. In practice, it is
impossible for the birds to achieve this theor-
etical threshold. Consequently, graded pro-
portions of the potential (e.g. 40%, 50% and
60% of
ND
max
T
) were used to calculate the
Lys, Met and Thr requirements for pullets.
Or:
ND
=
NR
max
T
× (
1
- e
-
b
×
NI
) -
NMR
Data obtained from the four trials were used
to determine
NMR, NR
max
T
, and
ND
max
T
, the
latter being calculated as the difference be-
tween
NR
max
T
and
NMR
.
PD
max
T
was calcu-
lated as
ND
max
T ×
6.25.
Because these parameters express the
theoretical potential for protein deposition
of the genotype studied, data from the four
trials were combined for further analysis.
Statistical analysis
The Gauss method of the NLIN procedure in
SAS software (version 9.2) was used to esti-
mate the parameter values in the above
equations. This method considers the sum
of the least squares of the distances between
the model and each point.
Amino acid efficiency
The efficiencies of utilization of the test
amino acids (
bc
-1
) were calculated using
data from T2, T3 and T4, which involved
individual limiting amino acids according
to the following equation:
b
= [ln
NR
max
T
- ln (
NR
max
T
-
NR
)]/
NI
Where
b
is the slope of the exponential func-
tion resulting from graded amino acid or pro-
tein supply and indicates the dietary protein
quality independent of
NI
.
The amino acid intake needed for a
given
NR
is determined using the following
equation, as derived by transformation of
the basic function, with
NI
being replaced
by intake of the
LAA
:
Results
Nitrogen balance
We studied chickens of the Dekalb White
strain throughout the same growth periods
in each of the trials. Therefore, the results
for all of the nitrogen balance periods within
equal age periods are summarized in
Table 20.3
.
As the content of the limiting nutrient
increased, the values for the
NI
,
NEX
and
nitrogen balance (
ND
) also increased. Birds
fed L1 had lower feed intake and body
weight compared to those fed diets with
higher protein contents, and the values of
these variables were almost constant for the
latter birds.
LAAI
= [ln
NR
max
T
- ln
(
NR
max
T
-
NR
)]/
16
·
bc
-
1
