Agriculture Reference
In-Depth Information
Table 19.2.
Proportion of summit basal used with the corresponding protein-free basal in the lysine (Lys),
methionine + cysteine (Met+Cys) and threonine (Thr) trials and the concentrations of limiting amino acid in
the resultant feed.
Summit basal
Levels
a
Trial
Lys
Met+Cys
Thr
Lys
Met+Cys
Thr
1
1.00
1.00
1.00
9.09
8.95
7.48
2
0.90
0.89
0.90
8.18
7.92
6.73
3
0.70
0.77
0.70
6.36
6.89
5.24
4
0.60
0.62
0.60
5.46
5.51
4.49
5
0.50
0.46
0.50
4.55
4.14
3.74
6
0.40
0.31
0.35
3.64
2.75
2.62
7
0.30
0.15
0.25
2.73
1.37
1.87
Control
+0.91
b
+1.39
b
+1.16
b
a
Digestible amino acid in g/kg.
b
Amount of amino acid added to control treatment.
to calculate egg output (g/bird/day). At the
end of each experiment all the birds were
weighed.
The data were analysed using a com-
pletely random design. All the variables had
their residuals tested for normality and
homoscedasticity using a Cramer-Von Mises
and Levene test. Data were analysed using
SAS PROC GLM 9.2 (SAS, 2008). The Read-
ing model (Fisher
et al
., 1973) was fitted to
the egg output and amino acid intake data
using EFG Software (2003) to obtain the
relevant coefficients of response according
to the model. Because the correlation between
egg output and body weight in laying hens
(
r
E
.
BW
) is close to zero (Fisher
et al
., 1973) a
simplified version of the Reading model was
used in this case:
Reading model describes the point of trunca-
tion, which cuts off an area equal to
ak
in one
tail of the normal distribution of egg output.
That is, it is the number of standard deviations
above the mean that omits an area equal to
ak
in one tail, where
k
= marginal cost of
1
mg
amino acid (Brazilian Reais (R) $/mg)/
marginal revenue of
1
g of egg output (R$/g).
Results
In all three experiments, responses obtained
with the control diet were significantly higher
than with treatment
7,
the lowest dilution in
the series, confirming that the amino acids
tested were limiting in the respective basal
diets evaluated.
The levels of the amino acids influenced
both feed intake and production as shown in
Table 19.3
. The maximum feed intakes in the
three assays were
106
g/bird/day,
105
g/bird/
day and
104
g/bird/day for Lys, Met+Cys and
Thr, respectively, these intakes occurring on
the fourth-highest level of amino acid con-
tents in each case. The mean intakes at the
lower amino acid levels were 0.32, 0.64 and
0.71 of the highest value observed, respect-
ively. However, higher inclusions of the three
test amino acids resulted in a reduction of
only 0.01, 0.03 and 0.06 of the highest intake
recorded.
Only the three lowest levels of each
test amino acid resulted in significant
mg
day
=×
A
a EbBW
+
×
opt
max
+
xa E
2
×σ
2
+ b
22
⋅σ
BW
max
E
max
= mean maximum egg output, g/day; σ
E
max
=
standard deviation of
E
max
;
BW
= mean body
weight, kg; σ
BM =
standard deviation of
BW
;
a
= intake of amino acid required per gramme
of egg output, mg;
b
= intake of amino acid
required per kilogramme of body weight, mg.
The optimum intake of the amino acid
(mg/bird/day) is that which leaves a proportion,
ak
, of the individual requirements unsatisfied
