Agriculture Reference
In-Depth Information
programme: for a given feeding schedule it
optimizes the amino acid contents and the
nutrient density of each feed, and the opti-
mum feeding schedule is determined, given
feeds of a fixed composition. These options
are described below.
these feeds in the feeding programme by
maximizing the objective function over the
entire growth period. As Fisher and Wilson
(1974) have shown, the optimum nutrient
density depends on such factors as sex, the
ratio between input and output costs, and
mixing and transport costs. These factors,
and others, may be considered by the user
in determining the optimum nutrient dens-
ity of each of the feeds in the programme.
Optimizing amino acid contents
in each feed
The optimum relationships between the es-
sential amino acids and energy change dur-
ing the growing period, and the optimizer
determines the relationship within each
specified feeding period that maximizes
(usually) or minimizes the objective func-
tion. The objective is to determine the opti-
mum amino acid to energy ratio in each of
the feeds in the feeding programme, such
that the overall performance (or objective)
is maximized. This differs from the tech-
nique previously described by Fisher and
Wilson (1974) in which the feed for each
given feeding period is optimized, because
the performance on one feed impacts on the
performance on subsequent feeds (Kyriazakis
et al
., 1991; Eits
et al
., 2003; Gous
et al
., 2012).
This is an essential prerequisite in optimiz-
ing the feeding of broilers, the optimum in
each phase changing as the feeding pro-
gramme changes.
To optimize amino acid contents the pro-
cess works only with lysine. The contents of
the other essential amino acids are controlled
by reference to an (user-defined) 'ideal' pro-
tein ratio in each phase of the programme. An
example of such ideal protein ratios is given
in Ajinomoto-Eurolysine (2013). The dietary
amino acid and energy contents may be opti-
mized simultaneously, or the user may fix
either of these while optimizing the other,
thereby increasing flexibility.
Optimizing the feeding schedule
Many broiler producers do not have the op-
portunity of having feeds mixed according
to their specifications, but are constrained
to make use of proprietary feeds. An almost
infinite variety of options is open to such
producers in designing their feeding sched-
ule, which can be based on amounts fed in
each period or on fixed feeding periods for
each feed. The optimum feeding schedule is
dependent on the composition of the feeds,
their respective prices, the revenue to be de-
rived from the sale of the broilers, and many
other biological and economic consider-
ations.
Response modifiers
A number of relationships between inputs
to and outputs from the model cannot be
simulated mechanistically. Pellet quality,
for example, which influences the mainten-
ance requirement for energy (Jensen
et al
.,
1962) may be modified by the content of fat
in the feed; lysine digestibility may be
modified by the crude fibre content (Giles
et al
., 1984); and the number of downgrades
due to hock burns, foot pad dermatitis, etc.
may be related to dietary protein content
(Nagaraj
et al
., 2007). These response modi-
fiers may be introduced empirically by the
user, who must specify the relationship be-
tween the modifier (e.g. feed fat content)
and the responder (e.g. feed fines). In this
way, the model accounts for user-defined
modifications when determining the opti-
mum feeds.
Optimizing nutrient density
Given an optimum ratio between the essen-
tial amino acids and energy within each
phase of the growing period, the program
will optimize the nutrient density in each of
