Agriculture Reference
In-Depth Information
Materials and Methods
efficiency of utilization of amino acids ne-
cessary for protein deposition are essential
to the development of models to estimate
amino acid responses (Edwards
et al
., 1997,
1999).
Methionine + cysteine (Met+Cys) and
threonine (Thr) stand out as two of the
first three limiting essential amino acids.
Methionine has a specific role in protein
synthesis, being the first amino acid to be
incorporated into the peptide structure,
and its deficiency may inhibit this early
stage (Kino and Okumura, 1987). Thr is
important in various metabolic processes
such as protein synthesis and maintenance
of body protein turnover; it has a role in
antibody production, as well as in the
maintenance associated with the digestive
tract, where it plays an important role in
the synthesis of mucins.
There are two main approaches for study-
ing the response of poultry to essential amino
acids: the dose-response method, which
measures the response in performance to
increasing intakes of the nutrient under test;
and the factorial method, which is based on
the principle that the animal needs amino
acids to maintain vital processes and activ-
ities, as well as for growth and/or production
(Sakomura and Rostagno, 2007).
The dose-response method has trad-
itionally been used to study the responses
of poultry to increasing concentrations of
amino acids in the diet. It is useful as a
means of providing components for the fac-
torial models (D'Mello, 2003a) such as the
efficiency of amino acid utilization, and
also to evaluate the factors that influence
this efficiency, thereby contributing to the
development of generalized models of nu-
trient responses.
This chapter describes the studies
conducted at the Poultry Science Labora-
tory of the Faculdade de Ciências Agrárias
e Veterinárias (FCAV) at UNESP-Jaboticabal
that have been aimed at assessing re-
sponses of broilers to increasing levels of
Met+Cys and Thr in the diet, their effi-
ciencies of utilization for growth and
their estimated intakes for optimum re-
sponses in the starter, grower and finisher
phases.
Six trials were conducted at the Poultry Sci-
ence Laboratory of FCAV, UNESP-Jaboticabal,
designed to measure the response of broiler
chickens during three phases of growth (
1-
14
days,
15-
28 days and
29-
42 days) to dietary
amino acids.
Five hundred and sixty male and 560
female broilers (totalling 1120 broilers)
were distributed in a completely random
design, according to a
7
×
2
factorial (seven
levels of dietary amino acids and two sexes)
totalling
14
treatments, with four repli-
cates. Each experimental unit comprised
20
birds. Cobb 500 broilers were used in all
the trials. At the beginning of each trial,
birds were individually weighed and dis-
tributed such that each experimental unit had
a homogeneous weight.
The experimental diets were formu-
lated using the dilution technique. A high
protein summit diet was formulated to
contain approximately 1.2 times the di-
gestible Met+Cys and Thr levels suggested
by Rostagno
et al
. (2005) for broilers during
the respective phases, and all other essen-
tial amino acids were set at a minimum of
1.4 times their suggested levels. These
summit diets were diluted sequentially with
isoenergetic, protein-free diets (nitrogen
free) (Fisher and Morris, 1970)
(Table 17.1
),
to create a range of feeds increasing in
content of the studied amino acids (Met
+Cys:
1-
14 days: 3.05 to 10.88 g Met+Cys/
kg;
15-
28 days: 2.72 to 9.79 g Met+Cys/kg
and
29-
42 days: 2.50 to 9.03 g Met+Cys/
kg) (Thr:
1-
14 days: 1.49 to 9.96 g Thr/kg;
15-
28 days: 1.30 to 8.86 g Thr/kg and
29-
42
days: 1.20 to 8.17 g Thr/kg).
To verify whether the studied amino
acid was limiting in the dilution series, a
pilot trial for each amino acid was con-
ducted with
30
male Cobb broilers from
1
to
14 days for Met+Cys and from
7
to 21 days
for Thr. They were distributed in a com-
pletely random design with two treatments
in each trial: the lowest studied levels for
each amino acid and the control treatment.
This treatment had the same nutritional
composition as the lowest treatment in the
dilution series, but it was supplemented
