Agriculture Reference
In-Depth Information
reducing costs, maximizing productivity
and complying with environmental legisla-
tion. In this scenario, fitting feed nutrient
supply to the nutritional requirements of
animals may considerably improve feed
efficiency.
Under practical conditions, nutri-
tional requirements are estimated using an
empirical or factorial method. The empir-
ical method uses the requirements for
maximizing or minimizing one or several
performance parameters. In the factorial
method, requirements are estimated as the
sum of maintenance and production re-
quirements. On the other hand, mathemat-
ical models are often based on the factorial
method to estimate nutritional require-
ments. These are technological tools that
allow not only growth and nutritional re-
quirements to be estimated, but also for
the different feeding scenarios applied in
different production systems to be simu-
lated. Consequently, production, environ-
mental and social aspects may be taken
into consideration when trying to estab-
lish nutritional and feeding strategies for
poultry.
Broiler growth models based on these
aspects have been developed in several
countries, such as the EFG broiler growth
model (EFG Software, 1995), the Pesti
Brill Model (Pesti
et al
., 1986) and
OMINIPRO (Fancher, 1999). These models
have been applied both in experimental
and commercial settings. In Brazil, mod-
elling is still rarely used as there are no
local models that can be applied as tools
to optimize poultry or pig production.
Aiming at filling this gap and stimulating
interest in modelling in Brazil, the Nutri-
tion and Modelling research group of
UNESP-Jaboticabal developed the Avinesp-
Model. This model estimates growth and
energy and amino acid requirements of
meat-type and egg-type chickens, as well
as simulating bird response under differ-
ent nutritional, feeding and environmen-
tal settings.
The objective of this chapter is to
present the theoretical background of
the AvinespModel, to describe its struc-
ture, to demonstrate how it was evaluated
and to discuss its implications and future
perspectives.
Theoretical Assumptions
of the Model
Feed intake is essential for animals as it
allows the animal to perform its biological
functions (Emmans, 1997). Under this con-
cept, it is assumed that the animal will try
to eat the amount of food it needs to fulfil
its requirement for the first-limiting nutri-
ent in the feed on offer (Emmans, 1997). In
a thermal-neutral environment it is assumed
that an immature animal needs energy only
for maintenance, which includes some
physical activity, as well as for protein and
lipid retention. Knowing the energy and
amino acid requirements of an animal for
maintenance and protein and lipid depos-
ition enables its nutrient requirement to be
calculated.
Maintenance and protein and lipid
deposition requirements of an animal not
subjected to nutritional restriction may be
expressed as a function of its protein weight
(Emmans, 1997) as these components and
animal growth potential are closely related
(Gous
et al
., 1999). Therefore, it seems rea-
sonable to propose that feed intake and nu-
tritional requirements of an animal can be
estimated as a function of its growth rate and
body composition.
Different genetic strains may present
differences in mature body weight expressed
in terms of protein, mature body compos-
ition (fat:protein ratio) and maturation rate
of body chemical components (water, pro-
tein, fat and ashes). These variables deter-
mine feed intake as well as energy and
amino acid requirements for the expression
of the genetic potential of each genetic strain
(Emmans, 1997, 1999).
The body changes from birth to mature
age: first, bones, viscera, feathers and muscles
are developed, and finally, the reproductive
organs. The ratio among these components
also changes as the animal ages. The math-
ematical description of these phenomena
helps to predict these changes with age
(Emmans, 1999). Therefore, the first step to
