INAVI: A Practical Tool to Study the Influence of Nutritional and Environmental Factors on Broiler Performance - Nutritional Modelling for Pigs and Poultry - page 111

Two submodels of similar architecture are
included: the first for the reference condi-
tions and the second for the simulation
conditions ( Fig. 9.3 ) . The simulation sub-
model is the only one connected to the re-
sponse laws, taking into account the effects
of environmental or nutritional factors on
the parameters controlling the energy flows
in INAVI. The reference submodel is only
used to describe reference conditions, con-
sidered as 'optimal' by the user, and to cali-
brate the two parameters IM and AF de-
scribed previously.
In reference conditions, we consider that
heat production ( HP ) is the expression of an op-
timal thermal balance. The principle of homeo-
stasis implies that the animal will modify its
metabolism in order to maintain this balance.
In INAVI, the optimal thermolysis capacity of

the animal is defined as the reference HP ( HP ref )
per unit of metabolic weight (kcal/kg 0.75 ):

HP ref = MEI ref - NED ref (9.10)
Thermolysis capacity = HP ref / BW ref 0.75

(9.11)

Similarly in the simulation submodel, HP is
calculated as:

HP = MEI - NED , if MEI > MEm + EPA
HP = MEm + EPA , if MEI ≤ ( MEm + EPA )

(9.12)

The thermostat is the expression of the ther-
mal balance of the animal with regard to an
optimal situation. It quantifies 'the energy ex-
cess' to be eliminated or the 'energy deficit' to be
filled, that is, the difference between thermoly-
sis capacity and simulated HP , calculated as

Reference input
Reference conditions
(feed/environment)

Scenario to be
simulated
New conditions
(feed/environment)

Reference
feed intake

MEI ref

Submodels
Response laws between
input (feed/environment)
and SubModel 2

MEI ref Corrected MEI

Mem ref
EPA ref

Adjustment

Mem
EPA

MEdc

Medc ref

Ed ref Ed

Thermostat

NED

NED ref

Ved ref Ved

HP
ref

HP
sim

Body weight
gain ref

Body weight
gain

To tal body
weight

To tal body
weight ref

Submodel 1: Reference Submodel 2: Simulation

Reference
performances
= Calibration of common
parameters between models
1 and 2 : Maintenance and
Physical activity

Output : Simulated
performances
= Feed intake, Body weight
gain, To tal body weight,
Feed conversion

Fig. 9.3. Simplified diagram of INAVI dynamic behaviour. INAVI includes two submodels ( 1 reference and
2 simulation) allowing the adjustment of performances to the reference taking into account the simulation scenario
(set of parameters), which acts on the simulation model thanks to specific response laws. The feed intake adjustment
of the reference submodel uses a retroactive thermostat loop that corrects the metabolizable energy intake ( MEI ).