Agriculture Reference
In-Depth Information
requirements of a modern strain of laying hen
for maintenance (mg/kg) and for egg output
(mg/g) using a dilution technique, and to use
the resultant coefficients of response to deter-
mine the optimum economic intakes of these
amino acids to achieve maximum profit.
and economic importance in promoting
growth and egg production. However, the
methods used to measure these responses
and the interpretation of the results of such
trials have been the subject of much discus-
sion and critical analysis in the literature
(Gous and Morris, 1985; D'Mello, 2003).
Nevertheless, in all cases a factorial ap-
proach, based on requirements for mainten-
ance and for production, has been used to
describe these responses, thereby allowing
for differences in body weight and potential
performance between strains and popula-
tions (Sakomura and Rostagno, 2007).
The optimum intake of amino acids
will differ between strains as a result of gen-
etic selection being applied differentially to
rate of egg production, egg size and body
weight (Pilbrow and Morris, 1974). For this
reason, responses to amino acids may need
periodic updating, but it is more important
to determine the optimum economic intake
of the limiting amino acids on a regular
basis, taking into account not only the po-
tential laying performance of the flock but
also the relationship between the marginal
cost of the amino acids and the marginal
revenue for eggs.
One of the many advantages of the
Reading model (Fisher
et al
., 1973) is that
it is a generalized model that describes the
response of any population of laying hens to
different amino acid intakes. Additionally, by
considering the inherent variation in egg out-
put and body weight the additional amount
of amino acid worth feeding above the mean
for the flock may be determined by consider-
ing the marginal cost and revenue associated
with the feeding of the limiting amino acid(s).
Pilbrow and Morris (1974) suggested that
there was an advantage in having the result
expressed as a daily intake (mg/g) and not as
a relative quantity (%) as this eliminates the
intrinsic factors that affect food intake. How-
ever, as the specifications in a least-cost feed
formulation exercise are expressed as con-
centrations and not intakes, the prediction of
food intake becomes essential if the optimum
intake of the limiting amino acid by the flock
is to be assured.
The objective of this research project
was to estimate the Lys, Met+Cys and Thr
Materials and Methods
Three trials were conducted over a period
of
2
years at the Laboratory of Poultry Sci-
ence, Faculty of Agriculture and Veterinary
Sciences, Universidade Estadual Paulista
(UNESP), Jaboticabal, São Paulo, to determine
the optimum economic amino acid intakes
of Lys, Met+Cys and Thr.
Three hundred and eighty four Dekalb
White laying hens were used in the Lys trial
and 476 in the Met+Cys and Thr experi-
ments. In each experiment the birds were
32
weeks of age at the start of the trial, and
in each case the experimental period was
divided into four periods of 28 days (
33-36,
37-40,
41-44
and
45-48
weeks of age).
A completely randomized design with eight
treatments and six replicates was used in
each case. All birds were distributed ac-
cording to body weight and egg production
to provide the same conditions for all treat-
ments at the beginning of the experiment.
The first
4-
week period was considered as
an adaptation period.
The lighting programme (16L:8D) used
was that recommended for the Dekalb White.
Temperature fluctuated during the Lys trial
between 32.9 ± 0.71°C and 12.8 ± 0.47°C and
the relative humidity between 90.9 ± 0.96%
and 35.3 ± 1.81%; for the Met+Cys trial the
numbers were 33.1 ± 0.45°C to 17.7 ± 0.3°C
and 77.0 ± 1.19% to 32.5 ± 1.42%; and for the
Thr trial, 31.7 ± 0.66°C to 19.1 ± 0.65°C and
80.2 ± 1.88% to 36.8 ± 2.69%.
The levels of each of the test amino acids
required in the test feeds were achieved by
blending a high protein summit basal with a
protein-free basal (Fisher and Morris, 1970).
Three summit basal diets were formulated
based on maize and soybean meal, the first
to contain 9.09 g Lys/kg, the second to contain
8.95 g Met+Cys/kg and the third to contain
7.48 g Thr/kg feed (
Table 19.1
)
. The minimum
