Basics and Applications of an Exponential Nitrogen Utilization Model (‘Goettingen Approach’) for Assessing Amino Acid Requirements in Growing Pigs and Meat Type Chickens Based on Dietary Amino Acid Efficiency - Nutritional Modelling for Pigs and Poultry - page 76

(I) ND max T = 3660 mg

3500

(II) ND max T = 2741 mg

2500

(III) ND max T = 1936 mg

1500

10- 25 days (I)
30- 45 days (II)
50- 65 days (III)

500

ND max T = NR max T ( 1 - e -NI · b ) - NMR

0 1000 2000 3000 4000 5000 6000

0.6 7

Daily nitrogen intake (mg/BW kg )

- 500

Fig. 6.2. Prediction of the ND max T of male meat type chickens (Ross 308) depending on age and making use
of diets with graded protein supply. (From Samadi and Liebert, 2008.)

animal protection regulations. As a conse-
quence the aim is not only to maximize diet-
ary protein content, but in addition to achieve
a high voluntary food intake. Incidentally,
the diet construction for this type of N re-
sponse experiment needs to fulfil a further
compromise: to ensure that the response to
protein utilization is not limited by other diet-
ary factors, the energy to protein ratio should
be held constant, but this is difficult to achieve.
An example of diet construction is given in
Tables 6.1 and 6.2 in which the difficulties in
preventing a decline in the energy to protein
ratio with high dietary protein contents are
demonstrated. Both of the tables demonstrate
that graded protein supply results in several
changes in dietary nutrient composition; starch
supply declines dramatically as the protein
content increases and has to be compensated
for by increasing fat supplementation to pre-
vent a significant loss of energy supply in the
diets.
As demonstrated in Table 6.3 , this prin-
ciple has also been applied in current studies
with male modern genotype meat type chick-
ens by Pastor et al . (2013). Diet formulation
for such experiments remains a compromise
between meeting the need for energy and
ensuring the efficient utilization of the graded
dietary protein supply. However, its success

depends on both the food intake pattern and
the concentration of energy in the diet.
Finally, these examples demonstrate how
it could be possible to achieve a response
curve to graded dietary protein supply that
is not under the influence of limiting factors
such as energy supply. A physiologically
based control is provided in an experiment
when the observed model parameter reflect-
ing dietary protein quality independent of
protein intake ( b ) remains unchanged. If
this precondition is fulfilled, the individual
N balance data can be utilized to estimate
the threshold value of NR max T and hence
ND max T . For this estimation several iteration
steps of the Levenberg-Marquardt algorithm
(Moré, 1977) within the program package
SPSS (19.0.0 windows) are required.
The N balance experiments of Pastor
et al . (2013) could demonstrate no significant
effect on parameter b ( Table 6.4 ) , indicating
that dietary protein quality in this study
was not limited by any factor other than
lysine supply. Under that precondition the
further application of the estimated thresh-
old value ND max T is justified, and valid-
ated estimates of the theoretical potential
from current investigations can be expected,
as demonstrated in Fig. 6.3 (Pastor et al .,
2013).