Agriculture Reference
In-Depth Information
Optimizing nutrient density
The results from this optimization exer-
cise are specific to the conditions described,
including the ingredient prices and rev-
enues, so they should simply be viewed for
illustrative purposes and should not be
used for commercial purposes.
In this example, three broiler feeds were
again offered using the same feeding pro-
gramme as above, but with the ratios between
the amino acids and apparent metabolizable
energy (AME) fixed in these feeds. Nutrient
density was optimized for males and females
reared separately, using two revenues (base and
base + 25%), and maximizing margin over feed
cost. The results are in
Table 13.5.
The optimum nutrient densities in the
initial feeds were higher for females than for
males, but the opposite was true in the final
feeding period. The optimum therefore in-
creased with each subsequent feed in the
feeding schedule in the case of males, but
decreased in the females. By increasing rev-
enue the optimum nutrient density in-
creased in the starter feed but this had no
effect on FCR or breast meat yield.
Optimizing the feeding schedule
In this case three feeds were again offered,
with fixed (
13
MJ/kg) AME contents and
with digestible lysine contents in the starter,
grower and finisher being 13.7, 12.4 and
11.0 g/kg, respectively. The objective func-
tion was to maximize margin over feed cost
for males and females separately at three
revenues, R10, R20 and R30/kg. The results
are in
Table 13.6
.
The optimum amounts of feed in each
period for the two sexes differed, sensibly,
Table 13.4.
Effect of using different objective functions on the optimum lysine levels in the three feeds
offered and on the predicted value of each objective at the optimum for each scenario. The four objective
functions chosen (scenarios A-D) were: maximizing margin over feed cost (A), maximizing breast meat yield (B),
minimizing feed conversion ratio (FCR) (C) and minimizing N excretion (kg N/flock of
30,000
birds) (D).
Dig. lysine (g/kg) at optimum
Margin over feed cost for each scenario
Scenario
Starter
Grower
Finisher
A
B
C
D
A
Maximize margin
over feed cost
(c/bird)
14.3
10.3
9.8
3131
417
1.591
1672
B
Maximize
breast meat
14.9
10.1
9.8
3127
419
1.593
1672
C
Minimize FCR
13.7
11.4
10.5
3086
413
1.536
1706
D
Minimize N
excretion
14.6
10.1
7.6
2989
393
1.714
1598
Table 13.5.
Optimum nutrient densities (expressed as MJ AME/kg feed), days to 2.3 kg, margin over food
cost, feed conversion ratio (FCR) and breast meat yield at 2.3 kg live weight of male and female broilers at
two revenues (base, and base +
25
%); the objective function maximized was margin over feed cost.
AME (MJ/kg) at optimum ND
Revenue
Rand/kg
Days to
2.3 kg
Margin over
food cost
Breast
g
Sex
starter
grower
finisher
FCR
M
Base
11.39
11.58
11.60
34
3202
1.768
408
M
+25%
11.44
11.59
11.58
34
4302
1.768
408
F
Base
12.77
11.59
10.79
38
3200
1.827
424
F
+25%
12.82
11.55
10.73
38
4486
1.830
424
AME = apparent metabolizable energy.
