Agriculture Reference
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processes that do not deposit protein. For
this reason, we used only the results of the
four most deficient levels of Met+Cys and
Thr to obtain their efficiencies of utiliza-
tion. We obtained similar values to those
found in the literature for Met+Cys and an
intermediate value for Thr (Edwards et al .
1997; Edwards and Baker, 1999; Stilborn
et al ., 2010).
Edwards et al . (1997) also reported
that the efficiencies of utilization of indi-
vidual amino acids are different, as observed
in this study. One explanation for this dif-
ference is that essential amino acids have
different degradation rates. When studying
Thr requirements for maintenance in the
chick, Edwards et al . (1997) found negative
Thr retention for the groups that received
diets with 0.05, 0.10 and 0.15 of the ideal
requirements, and an efficiency of Thr util-
ization of 0.82. In another study, Edwards
and Baker (1999) observed only positive
retention in chicks fed graded levels of
Met+Cys. But in this case the efficiency
of  utilization was only 0.52, a reflection
of  the diverse functions of methionine
beyond its role in protein synthesis
(D'Mello, 2003b).
The Met+Cys intakes for maximum re-
sponse reported here are in accordance with
the findings of some other authors. The in-
take to maximize FCR exceeded that for
maximizing body weight gain (Schutte and
Pack, 1995; Baker et al ., 1996; Mack et al .,
1999) suggesting that at marginal deficien-
cies of methionine birds consume more feed
to meet their requirement. Chamruspollert
et al . ( 2002) have also reported a higher me-
thionine intake to maximize protein synthe-
sis in broiler chicks when compared to that
for maximum growth, as found in this trial,
suggesting that methionine should be sup-
plemented in starter diets so as to reach the
maximum protein synthesis and maximum
lean body yield, but that this was not as im-
portant in the grower and finisher phases, as
these requirements are very close to each
other.
However, the intake of Thr to maximize
body weight gain exceeded that for maximum
FCR. This result is contrary to the findings
of Kidd and Kerr (1997) and Baker et al .
(2002) who found that the intake required
to maximize BWG and FCR was the same.
On the other hand, Mack et al . (1999) and
Ahmadi and Golian (2010) found that in-
take of Thr had to be higher to maximize
FCR than that required to maximize BWG.
This could be due to the formulation tech-
nique used in the present trial, which re-
sulted in less change in carcass composition
over the range of Thr intakes than in the
case of Met+Cys. More energy is required
for fat deposition than for protein depos-
ition (Wallis, 1999), which may also explain
the difference in intake of Thr required to
maximize body weight gain and protein
gain, especially for female broilers, which
deposited more fat than males.
In conclusion, the efficiency of utiliza-
tion of Met+Cys and Thr as measured in
these trials for both male and female broil-
ers are, respectively, 0.56 and 0.73. The
Met+Cys intakes for minimum FCR were
231 mg/day (7.00 g/kg) and 524 mg/day
(4.68 g/kg) in the starter and grower phases,
for both males and females, and 923 mg/day
(5.27 g/kg) and 1053 mg/day (5.40 g/kg) for
females and males, respectively, in the in-
isher phase. Thr intakes were 184 mg/day
(5.58 g/kg), 612 mg/day (5.46 g/kg) and 823
mg/day (4.45 g/kg) in the starter, grower and
finisher phases, respectively, for both males
and females.
The knowledge of how broilers respond
to incremental intakes of amino acids en-
ables the nutritionist to define optimum
economic intakes of different amino acids,
but to convert these into dietary concentra-
tions for feed formulation purposes the ex-
pected food intake of broilers needs first to
be predicted.
Acknowledgements
The authors would like to acknowledge
Fundação de Amparo à Pesquisa do Estado
de São Paulo (FAPESP) for financial sup-
port for this project and scholarship.
 
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