Agriculture Reference
In-Depth Information
broiler production requires understanding
of most of the mechanisms leading to a
given level of production within a poultry
shed. The model described in this chapter,
called INAVI (as a contraction of INRA (re-
search institute) and ITAVI (extension ser-
vices)), to stress its double purpose (i.e. to
be useful for both practitioners and re-
searchers), is proposed below to contribute
to this aim.
In a nutshell, INAVI is a mechanistic,
dynamic and deterministic model that at-
tempts to integrate at the broiler scale a large
set of biological mechanisms and response
laws to nutritional and environmental para-
meters. It aims to simulate broiler growth in
contrasted conditions for a large range of
broiler breeding lines. However, as for most
models, INAVI has to be seen more as a tool to
enhance the thinking of researchers and prac-
titioners rather than as a prediction tool. The
team (M. Quentin, M. Picard, I. Bouvarel;
Quentin, 2004) that developed INAVI chose
the simplest possible representation to allow
both iteration steps and the possibility for
every stakeholder to cope with the whole
model and therefore to implement new ideas
on their own. The description and examples
given below illustrate this aspect of an 'open
to change by the user' model and underline
the never-ending process of modelling broiler
growth.
Broiler Growth in INAVI:
An Energetic Point of View
The broiler models of Hurwitz
et al
. (1978)
and Emmans (1981) use body composition
for predictions of both resource require-
ments and feed intake. The main objective
of INAVI (
Fig. 9.1
) is the simultaneous
adaptation of intake and growth with energy
use as the main driving force. The aim of the
energy model is not to calculate require-
ments but rather to describe the use of in-
gested energy for growth.
MEI
MEm
EPA
HP
MEdc
Ed
NED
Ved
Body weight gain
To tal body weight
Fig. 9.1.
Simplified energy model of INAVI. Ingested metabolizable energy (
MEI
, in kcal) becomes energy
available for growth (
MEdc
, in kcal) after withdrawing maintenance requirements (
MEm
, in kcal) and
losses for physical activity (
EPA
, in kcal). A fraction of MEdc is deposited, as net energy deposited (
NED
)
transformed in body weight gain (in grammes) accumulated in total body weight. Body weight is used to
determine
MEm
and
EPA
. The fraction of
MEdc
deposited as
NED
is defined as the efficiency of energy
deposition (Ed). Body weight gain is determined from
NED
as a function of the energy content of the
weight gain deposited (
Ved
, in kcal/g). Heat production (
HP
) is calculated by difference between
MEdc
and
NED
.
