Agriculture Reference
In-Depth Information
Fig. 1.1.
An example of the look-up facility in INAVI. Allows modification of the coefficient of adjustment
of the effective temperature (Output data) as a function of air velocity (Input data) for temperatures higher
than 26°C. (The underlying relationships were based on the results of Yahav
et al.
(2001); taken from
Quentin (2004).)
'homeorhetic regulations in the decisional
system constitute <pull> driving forces that
define the genetic potential of the animal as
a dynamic balanced state controlled by both
protein and lipid retention in the body com-
partments of the operational system'. Pro-
tein and lipid retention in carcass, viscera
and feathers are controlled by defined frac-
tional rates of synthesis and degradation.
Deviations from the desired (balanced) body
weight gain of the genetic potential are con-
trolled by homeostatic regulations that act
to limit the difference between actual growth
and the balanced state (as defined by the
homeorhetic regulations) and the flows of
nutrients (fatty acids, amino acids, glucose
and 'energy' as acetyl-CoA) among the com-
partments of the operational system. The
development of the model is discussed by
Rivera-Torres
et al
. (2010).
This model appears to be driven by the
'genetic' parameters governing the rates of
protein and lipid turnover. These are inputs
to the model and the turkey is assumed to
eat food to achieve this potential growth. To
that extent the model derives from the theory
proposed by Emmans (1981). The calcula-
tion of turnover also leads to the determin-
ation of feed intake in energetic terms and
these parameters also control the <pull>
driving forces of the 'decisional' compartment
of the model. Experiments to determine
these important 'genetic' parameters are not
described and the authors state that 'model
calibration was mostly performed manually'.
This seems to have been done to give model
outputs that correspond to experimental
data. Although this was done separately for
male and female turkeys, it is not clear how
the parameters would be adjusted for differ-
ent genotypes or to allow for genetic changes
in the future. Of the
42
parameters used in
the model,
22
were assumed to be constant
and derived from a variety of sources,
15
were
estimated manually from the data as above
and
5,
which describe the diet, are user-
defined. The determination of the tissue
turnover parameters is very critical since
the sensitivity of model outputs to changes
in parameter values is quite high. Thus a
±5% change in the two parameters of car-
cass protein anabolism changed estimated
