Agriculture Reference
In-Depth Information
indications about the efficacy of protein util-
ization processes as a whole (NPU) or limited
to post-absorptive utilization (BV). The latter
was achieved by relating N retention data to
the uptake of truly digested feed protein. In
addition, measurement of the balance of the
gastrointestinal tract (GIT) as a parameter of
nutrient digestibility provided additional
information about nutrient efficiency at the
absorption level.
In principle, this was the situation when
the basic concept for the 'Goettingen ap-
proach' was developed by Gebhardt (1966)
in the last century, based on N balance experi-
ments with the laboratory rat. A significant
background for this research was the observed
limitation for applying traditional proced-
ures to describe the complex protein value
of individual feedstuffs or protein mixtures
independent of the actual level of dietary
protein supply. Similar problems with pro-
tein evaluation systems for human nutrition
were an additional driving force at this time.
Consequently, first developments of the basic
approach of Gebhardt (1966) were focused
on standardization of individual protein val-
ues to improve comparability of feed protein
sources. This application is still in use but
is currently more interesting for evaluation
of the complex protein value of mixed feeds.
However, the field of applications for the
approach was, in the meantime, significantly
extended and also adapted to the current
expectations of research in protein nutrition
of food-producing animals. Details of these
developments and applications are described
subsequently. However, it will not be pos-
sible to outline in detail how the different
issues of the current procedure differ from
other approaches that are in use. Conse-
quently, further descriptions will be focused
on important steps of development and ap-
plications of the exponential N utilization
model as basically proposed by Gebhardt
(1966), but will not include a discussion as
related to other procedures. Actually, studies
have been initiated to provide amino acid
requirement data by simultaneous applica-
tions of both supplementation technique
and the Goettingen approach. However, the
results are still under investigation and will
be discussed below.
Exponential N Utilization Model
('Goettingen Approach')
Background for developments
The basic scenario is illustrated in
Fig. 6.1,
showing that the traditional procedures may
evaluate a low quality feed protein at a low
level of uptake as equal to a high quality
Retention : Intake
High dietary protein quality
Low dietary protein quality
Dietary protein supply
Fig. 6.1.
Effect dietary protein supply on observed net protein utilization (NPU) and consequences for
derived dietary protein quality depending on protein supply.
