Agriculture Reference
In-Depth Information
the first two phases. The third phase is as-
sociated with the growth of the organs in-
volved in sexual maturation and in the fourth
phase, weight gain is related to body fat de-
position.
The combined effects of genotype and
environment can affect the number of phases
and generate a few common assumptions
that justify the need to use multiple phases
to describe growth (Grossman and Koops,
1988; Kwakkel et al ., 1993, 1995).
Protein growth in a laying pullet can be
partitioned into three compartments, namely
feather, feather-free body (Emmans, 1989) and
reproductive organs (Bowmaker and Gous,
1989) based on differences in the growth rates
of each component, which are specific to each
genotype. The resultant growth is the sum
of these components.
The aim of this study was to describe the
growth of feathers, feather-free body, repro-
ductive organs and liver of Dekalb White lay-
ing pullets from 1 day old to sexual maturity
for integration into a model to determine the
daily requirements for lysine (Lys), methio-
nine + cystine (Met+Cys) and threonine (Thr)
of a pullet during growth.
The parameters estimated for each component
were: Pm , protein weight at maturity (kg); B ,
rate of maturing (in days); and t* , the age at
maximum growth rate (days), where Pt is
weight at time t (kg), t is the bird's age (days)
and e is Euler's number.
Feather protein weight ( FP ) was corrected
for the loss of feathers occurring between
sampling periods. This correction consisted
of adding feather protein loss to the observed
weights. Feather protein loss was defined as
0.04 g/day (Silva, 2012). The corrected fea-
ther protein weight ( FP C ) was applied to
Eqn 16.1 to estimate the corrected growth
parameters.
The rate of protein deposition ( PD ) (g/
day) of each component was calculated using
Eqn 16.2:
PD = B × Pt × ln ( Pm / Pt )
(16.2)
Where ln is the natural log. Given B , Pm
and e , the maximum protein deposition
( PDmax ) was calculated in g/day: PDmax =
B × Pm / e .
The rates of deposition of Lys, Met+Cys
and Thr in each component were obtained
by multiplying PD by their corresponding
amino acid contents in the feather and
feather-free protein. The same amino acid
composition that was used for the feather-free
body was used for the ovary, oviduct and
liver.
Materials and Methods
The studies were conducted in the Laboratory
of Poultry Science, Faculty of Agriculture
and Veterinary Sciences, UNESP-Jaboticabal,
São Paulo, Brazil.
Description of the model for determining
amino acid requirements
Description of growth
To estimate the daily Lys, Met+Cys and
Thr requirements for potential protein
growth the factorial model of Martin et al .
(1994) was used, to which was added the
growth of ovary, oviduct and liver from
15 weeks of age. The amino acid require-
ments were established separately by con-
sidering the rates of amino acid depositions
of five components (feathers, feather-free
body, ovary, oviduct and liver) and the effi-
ciency of amino acid utilization. The mainten-
ance requirements of feather and feather-
free body protein were also considered
Dekalb White pullets were weighed and sam-
pled at 0, 14, 28, 56, 70, 98 and 112 days of age
in order to determine the weights of feather-
and feather-free protein at those ages. Weigh-
ing and sampling of the ovary, oviduct and
liver took place at 105, 112, 119, 126, 133,
140, 147 and 154 days. The Gompertz (1825)
equation (Eqn 16.1) was fitted to these data
to determine the potential rates of growth of
these components:
Pt = Pm × e e B × t t *
(16.1)
 
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