Agriculture Reference
In-Depth Information
estimate nutritional requirements is to de-
scribe a genotype's growth, which is usually
estimated using the Gompertz function.
Rates are expressed on a daily basis, energy
in megajoules and mass in grammes.
Body Protein Deposition Potential
Model Description
The Gompertz (1825) equation is used in
this model to describe protein deposition
based on three biologically meaningful para-
meters: maturation rate (
B
), protein mass
at a moment in time (
Pt
) and protein mass
at maturity (
Pm
). The derivative of the
Gompertz equation describes the potential
protein growth rate (
pPD
), according to Ferguson
et al
. (1994). Equation parameters are ob-
tained by fitting a non-linear model to growth
data (Hancock
et al
., 1995):
pPD
=
B
×
Pt
× ln(
Pm/Pt
) (g/day)
The model proposed here is based on a
theory that developed over time (Emmans,
1974, 1981, 1987, 1994, 1999). The general
structure of the model follows the pro-
posal of Ferguson
et al
. (1997), although
here it is used for chickens, not for pigs
(
Fig. 14.1
).
The model estimates
ad libitum
feed
intake, live weight, body composition and
nutritional requirements of broilers and
layer replacement pullets. It also estimates
the response of an average chicken to a
given feed and environment. Diet compos-
ition and chicken genotype are considered
model inputs. Actual protein and lipid
body mass are used as body state variables.
The effective energy (EE) system, as pro-
posed by Emmans (1994), is applied. Euler's
integration method was applied to solve
equations with
1-
day integration steps (
dt
).
This equation indicates that the growth rate
of an animal depends on its current state.
Potential protein deposition will only be
achieved if sufficient energy and amino
acids are supplied.
Body protein deposition potential will
be achieved only if the chicken consumes
adequate amounts of all essential nutrients;
External
effect
Animal
Maintenance
Growth
Gut capacity
Feed
Requirement
Environment
Desired intake
and growth
Constrained
intake and
growth
Actual intake and growth
Nutrient requirements
Nutritional strategies
Manure
Fig. 14.1.
General description of the AvinespModel to estimate growth and nutritional requirements.
