Agriculture Reference
In-Depth Information
Total amino acid concentrations in the diets
and excreta were determined by high per-
formance liquid chromatography (HPLC).
BWG (g/bird/day), digestible amino
acid intake (Met+Cysi
i
or Thr
i
, mg/day, cal-
culated from the feed intake), feed conver-
sion ratio (FCR, g/g) and the proportion of
feathers in the body weight (PF) were calcu-
lated from the measurements of body weight
and feed intake taken during each phase of
growth. The deposition of protein and lipid
(g/day) in the feather-free body and in the
feathers was determined using the compara-
tive slaughter technique. The number of
birds sampled at the beginning of each
phase was six, while two birds in each ex-
perimental unit were sampled at the end of
each phase of the trials.
The amino acid content of protein in the
feather-free body and in the feathers was meas-
ured in birds sampled at the beginning and the
end of each phase and was analysed by HPLC,
from which the amount of amino acids depos-
ited during each phase was calculated.
The efficiency of utilization of Met+Cys
and Thr was obtained by linear regression
of the amino acid deposited in the whole
body (feather-free body + feathers) on di-
gestible amino acid intake. The amino acid
intake for growth was calculated by sub-
tracting the maintenance requirement from
the total consumed. To ensure that only the
linear portion of the response was used for
this regression the lowest four levels of
Met+Cys and Thr were used.
The amino acid requirements for mainten-
ance used in the calculations were those meas-
ured by Bonato
et al
. (2011), namely
24
mg
Met+Cys/kg
0.75
/day and
50
mg Thr/kg
0.75
/day.
A statistical analysis of variance was
conducted on each of the variables measured.
Linear response plateau and quadratic poly-
nomial models were fitted to the data. To es-
timate the optimum amino acid intake both
models were used, since the point where the
quadratic curve first intersects the plateau of
the broken line is considered 'a realistic and
objective estimate of the requirement for a
population of animals' (Baker, 2003). To ex-
press optimum amino acid intakes as concen-
trations in the diet, the mean feed intakes sug-
gested by Cobb-Vantress (2009) were used,
for females and
34
g/day,
116
g/day and
195
g/day for males, during the starter, grower and
finisher phases, respectively.
Results
The mean amino acid intakes, body weight
gains, feed conversions and feather propor-
tions in broilers subjected to increasing
dietary levels of Met+Cys are presented in
Table 17.2
and of Thr are in
Table 17.3
.
Figure 17.1
illustrates the response in terms
of weight gain as a proportion of its max-
imum value, to the reduction in intake of
each amino acid.
Results of the pilot trials confirmed that
Met+Cys and Thr were the limiting amino
acids in the respective dilution series. The
addition of synthetic Met+Cys and Thr to the
feed with the lowest contents of these amino
acids improved both BWG (7.79 g/bird/day
vs 5.18 for Met+Cys and 30.1 g/bird/day vs
27.6 for Thr) and FCR (2.65 g/g vs 2.98 g/g for
Met+Cys and 2.28 g/g vs 2.45 g/g for Thr).
For Met+Cys
(
Table 17.2
)
gender influ-
enced the responses in BWG after 14 days,
but with FCR this effect was only significant
in the last phase. The reduction to 0.19 of
the maximum Met+Cys intake in the starter
phase reduced BWG to 0.36 of the max-
imum response. For the grower and finisher
phases, reducing Met+Cys intake to approxi-
mately 0.32 of the maximum, regardless of
sex, reduced BWG to 0.48 and 0.54 of the
maximum gain for both males and females,
respectively, in the grower phase, and to
0.65 and 0.57 of the maximum gain for both
males and females, in the finisher phase.
These responses are illustrated in
Fig. 17.1
.
Gender differences in the responses in
BWG in the Thr trial (
Table 17.3
) are appar-
ent in all phases, but no such effect was ob-
served in FCR. A reduction to 0.06 of the
maximum Thr intake resulted in a reduc-
tion to 0.13 of maximum BWG in the starter
phase, regardless of sex. In the grower and
finisher phases, reducing Thr intake to ap-
proximately 0.13 of the maximum reduced
BWG to 0.20 of maximum gain, regardless
of sex during grower phase, and to 0.30 and
0.28 of maximum gain for males and females,
respectively, in the finisher phase.
