Agriculture Reference
In-Depth Information
of field data was used to calibrate the model
for seasonal temperature effects and to cal-
culate lag periods between a change in tem-
perature and the response in feed intake
and growth. Again some complex empirical
relationships were introduced; for example,
in birds less than 90 days of age the effi-
ciency of protein retention was described
by the equation:
Z
= 0.78 × exp(0.1851 - 0.01681
A
+ 0.0000962
A
2
- 0.0000001
A
3
) (1.3)
digestive tract and for 'passage ability' mak-
ing the model similar to the one described
by Emmans (1981). The model considers
mortality, stocking density effects and a de-
scription of an environmental control sys-
tem to provide a complete description of the
production process. There are many inter-
esting ideas in this paper and the authors
state that 'efforts for further qualification of
the model are aimed at using it for economic
off-line process control and in future as a
software solution for a computer-aided op-
erative on-line process control in practice'.
No evidence of such further developments
has been found in the literature.
The models described by Dänicke (1995
- available only in summary form) and
Roan and Wang (1996) have not been re-
viewed in detail in the preparation of this
chapter but are included for completeness.
Novák, L. (1996) describes a self-regulating
growth model in homeothermic animals
that has been applied to the description of
broiler growth (Novák and Zeman, 1997;
Novák
et al
., 2004). Inputs to the model in-
clude initial body mass, genetically limited
(mature) body mass and daily food intake.
Daily growth is then calculated mainly in
terms of energy transactions. Novák (2003)
describes the idea that the effects of various
stressors on growth can be represented by
increased maintenance energy require-
ments. These effects may be calibrated for
known energy transactions, for example,
for a cold environment, but in general it
appears they can be determined only by
empirical adjustment.
It is difficult to give a summary of the
broiler growth model described by King
(2001); this work illustrates very well the
problems of describing a model in the litera-
ture. The calculations of growth appear to
be driven by either user-provided feed in-
take data or empirical feed intake data based
on polynomial analysis of two pens of birds.
Intake data at
7-
day intervals are expressed
as 'Repletion Units' (
RU
), which take account
of the energy and protein content of the feed
as follows:
Where
Z
is the conversion of available pro-
tein to body protein above maintenance
and
A
= age in days. The source of this
equation, and therefore the opportunity to
evaluate it, is not described. The model was
evaluated by comparison with a large set of
commercial data. The authors describe the
model in the context of restricted feeding in
both egg laying and breeding stock. How-
ever, it is difficult to see how fully con-
trolled feeding would be considered since
the model is driven by energy intake calcu-
lated from growth. Also in breeding birds
the most important economic responses to
restricted feeding are in reproductive per-
formance and these are not considered in
this work.
The extensive works of Burlacu (G. and R.)
on modelling poultry and pig systems have
not been reviewed in the preparation of this
chapter. A broiler model for energy and
protein balance simulation is described by
Burlacu
et al
. (1990).
Grosskopf and Matthäus (1990) describe
a mathematical simulation of a complete
broiler production system with economic
evaluation on a live weight basis. A broiler
compartment calculates the growth of a sin-
gle animal, the poultry house compartment
includes climate factors and mortality and
corrects feed intake for temperature and
stocking density effects, while the economy
compartment places the results in a finan-
cial framework. The model contains a series
of mechanistic functions but the source of
the parameterization is not revealed. The
model is driven by the assumption that
birds fed
ad libitum
aim to eat enough feed
to achieve their genetic potential. This is
then adjusted for the intake capacity of the
RU
(per g diet) =
2
×
TME
+ (1.65 ×
5.739 ×
CP
) ×
Q
(1.4)
