INAVI: A Practical Tool to Study the Influence of Nutritional and Environmental Factors on Broiler Performance - Nutritional Modelling for Pigs and Poultry - page 117

commercial broilers of 28 days of age be-
tween 15°C and 32°C. They showed that a
decrease of 1°C in temperature resulted in
an increase of 2.3% in HP ( Fig. 9.5d ). Equa-
tion 9.10 is then multiplied by this VF to
estimate the thermolysis capacity in simula-
tion conditions.

(<0.5 mm) content (%), level of primary
limiting amino acid (%).
Environmental conditions: average indoor
temperature (°C), average indoor relative hu-
midity (%), animal density (birds/m²) and
air speed (m/s).

Step 2: calibration of the model

physical activity . When reared in cold con-
ditions (i.e. below 'optimal' temperature),
broilers spend more time feeding, which in-
creases their physical activity (and helps to
produce heat). Because data were missing,
the effect of cold on physical activity was
adjusted from the equations of Howlider
and Rose (1987). In INAVI, a decrease of
10°C below 'optimal' temperature induced
an increase in physical activity of 40%.
Above 'optimal' temperature, we considered
that the decrease in physical activity with
increasing temperature was of the same order
of magnitude (Fig. 9.5d) .
Hurwitz et al . (1980) measured the effect
of the ambient temperature on maintenance
requirements of broilers from 4 to 9 weeks of
age. The influence was found to be linear
with a decrease in MEm of 1.32% when tem-
perature is increased by 1°C (Fig. 9.5d) .

The calibration step is essential in the use of
INAVI in order to fit two parameters (index
of maintenance, IM , and the activity factor, AF )
according to the reference performances ob-
served by the user. These two parameters are
considered to be representative of the geno-
type and will be used to calculate reference
heat production, which is necessary for the
adaptation of feed intake by the thermostat.
The calibration is carried out with VEN-
SIM ® , whereby the user modifies the values
of IM and AF manually with cursors in order
to fit the reference performances calculated
by the model to the reference performances
observed by the user ( Fig. 9.6 ) . After that,
obtained values of IM and AF must be manu-
ally noted in the Excel sheet to be used later
for the simulations.

Step 3: simulations

From the Conceptual Model to a
Practical Tool: Evaluation of
Performances in New Conditions,
a Three-step Simulation

The simulation process requires the descrip-
tion of the simulation conditions in the
same Excel sheet. To that purpose, the user
must fill out two tables containing feed char-
acteristics and environmental conditions of
the simulation (with the same variables as
for the description of reference conditions).
The simulation is then launched from VEN-
SIM ® and takes only a few seconds.

Step 1: description of reference
and simulation conditions

A Microsoft Excel ® sheet is used to describe
the reference conditions. The studied age
period and the reference physical activity (%),
which is considered to be representative of
the genotype, are first described.
Three tables are then filled out to de-
scribe, on a daily basis, the reference condi-
tions:

Examples of Simulations

Two examples are given to illustrate how
INAVI might be used to assess the impact
of nutritional and environmental factors
on broiler performances (growth, intake). In
order to easily compare these simulations,
the reference scenario will be identical for

Daily performances: feed consumption
(g) and weight gain (g).
Feed characteristics: ME content (kcal/
kg), crude protein content (%), fine particles