Agriculture Reference
In-Depth Information
their reproductive organs) pullets need an ad-
equate supply of nutrients during growth; the
supply of amino acids is particularly import-
ant for body protein synthesis.
To achieve the optimal content and dietary
ratio of amino acids it is necessary to deter-
mine both the efficiency of amino acid util-
ization and the rate of protein deposition
(Baker
et al
., 2002). Several methodologies
have been proposed to determine these
parameters (Emmans, 1989; Martin
et al
., 1994;
Edwards and Baker 1999; Sakomura and Ros-
tagno, 2007). However, these procedures util-
ize large numbers of animals and require the
slaughter of a relatively large number of birds
to measure their responses. Researchers at
Georg-August-University in Goettingen, Ger-
many, have proposed another approach. They
have published studies based on factorial
models using dose-response parameters
obtained in nitrogen balance trials (Samadi
and Liebert, 2006 a,b, 2007a,b, 2008; Liebert,
2008, 2013; Wecke and Liebert, 2013).
This approach makes use of a non-linear
mathematical model to estimate the efficiency
of amino acid utilization (
bc
-1
) taking into ac-
count the theoretical maximum for daily ni-
trogen deposition (
ND
max
T
) and the nitrogen
maintenance requirement (
NMR
) for deter-
mination of amino acid requirements.
Most studies have been conducted using
broiler chickens (Samadi and Liebert, 2006b,
2007a,b, 2008; Wecke and Liebert, 2013),
swine (Thong and Liebert, 2004; Wecke and
Liebert, 2009, 2010) or fish (Liebert, 2009).
However, up to now no studies have been
performed using pullets. The current study
was designed to determine the amino acid
requirements of pullets based on the Goettin-
gen approach.
the nitrogen maintenance requirement (
NMR
)
and the theoretical maximum for daily ni-
trogen retention (
NR
max
T
). The last three NB
trials were performed both to determine the
efficiency of lysine (Lys), methionine (Met)
and threonine (Thr) utilization (
bc
-1
) and to
estimate the requirements for these amino
acids of Dekalb White pullets in various
growth phases (I:
14
to 28 days; II:
56
to 70 days;
and III:
96
to 112 days). The procedures
applied in this study are in accordance with
earlier reports (Thong and Liebert, 2004;
Samadi and Liebert, 2006a, b, 2007a,b, 2008;
Liebert, 2008, 2009; Wecke and Liebert,
2009, 2013) performed to estimate the
NMR
,
NR
max
T
, efficiency of amino acid utilization
and amino acid requirements making use of
NB trials.
Animals, housing and experimental design
A total of 360 Dekalb White birds was used
in the trials. Management of the pullets and
the lighting programme used followed the
recommendations of the pullet management
guide. The experimental design was com-
pletely randomized, with six treatments and
five replicates of one bird per cage. At the be-
ginning of each phase the body weight of the
birds in the experimental units was stand-
ardized. Pullets were housed in metabolic
cages with a floor space of 0.25 m
2
/bird.
Dietary treatments
Prior to the start of each experimental period
the birds received diets formulated accord-
ing to the recommendations of the Brazilian
Tables for Poultry and Swine (Rostagno
et al
., 2005).
The first trial (T1) was conducted using
graded dietary protein supply to determine
the
NMR
and
NR
max
T
of the Dekalb White
genotype (
Table 20.1
). Three trials (T2-T4)
were conducted to estimate the model param-
eters (
NMR
,
NR
max
T
) and efficiency of util-
ization of Lys, Met and Thr, respectively.
The dietary treatments consisted of five levels
of graded amino acid supply from equal protein
Materials and Methods
Four nitrogen balance trials were conducted
in the Laboratory of Poultry Sciences of the
Faculty of Agriculture and Veterinary Sciences,
Universidade Estadual Paulista, Jaboticabal,
São Paulo, Brazil.
The model parameters determined in
these four nitrogen balance (NB) trials were
