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 84

due to this deletion the observed AA effi-
ciency ( bc -1 ) is elevated indicating the change
from an adequate or excess AA supply to a
limiting supply of the individually deleted
AA in the dietary protein. The value of bc - 1 is
generally not valid for further applications
within the model if the individual AA effi-
ciency is not measured under guaranteed
limiting position. Otherwise the observed in-
crease in bc - 1 in the deleted diet alone is not
sufficient for a validated limiting position. A
significant decline in protein quality (model
parameter b ) needs to be observed to ensure
this important limiting position of the AA
under study. Misleading conclusions about
IAAR s can be expected if this precondition
for valid model application is not fulfilled.
A summary of our current results based
on several N balance studies in meat type
chickens, in which the ingredients used did

not differ much from feeding practice, is
given in Table 6.9.
As demonstrated, the observed IAAR s in
growing chickens are not yet consistent and
some earlier conclusions about IAAR s are
not supported. This is especially the case
for the branched chain AAs (BCAA), where
available requirement recommendations
are not sufficiently well founded. However,
if the current conclusions about IAAR s are
more valid than earlier assumptions, it should
be possible to prove the response in protein
utilization in the animal. Some initial studies
in growing chickens have been conducted
that deal with this important question. In spite
of the fact that data evaluation from these
experiments is still not finished, initial re-
sults indicate that the reevaluated IAAR s
( Table 6.9 ) yielded elevated dietary protein
quality data as compared to the average

Table 6.8. Summarized ideal dietary AA ratios ( IAAR s) for growing chickens as derived from current studies
with meat type chickens in two age periods. (From Wecke and Liebert, 2013.)

Lysine Threonine Tryptophan Arginine Isoleucine Valine

Starter period
Mean a 100 60 19 105 55 63

Grower period
Mean a 100 62 17 105 65 79

a Summary of three experiments.

Table 6.9. Comparison of observed IAAR s from N balance studies in growing meat type chicken depending
on age.

Pastor et al ., 2013 Wecke and Liebert, 2013

AA Average a AA-balanced diet Starter Grower Starter Grower

Lysine 100 100 100 100 100 100

Methionine 40 38

Met+Cys 74 74

Threonine 66 65 60 62

Tryptophan 16 17 19 17

Arginine 105 106 105 105

Histidine 34 34

Isoleucine 69 68 55 56 55 65

Valine 80 79 65 72 63 79

Leucine 110 110 94 106

Phenylalanine 66 66

Phe+Tyr 120 118

a According to Table 6.7.