Agriculture Reference
In-Depth Information
Requirements for Growth and Sexual
Development in Laying Pullets
E.P. Silva,
1
N.K. Sakomura,* L. Hauschild
1
and R.M. Gous
2
1
Universidade Estadual Paulista, Jaboticabal, São Paulo Brazil;
2
University
of KwaZulu-Natal, Pietermaritzburg, South Africa
Abstract
Growth in a laying pullet prior to sexual maturity can be partitioned into three components: feathers,
the feather-free body and reproductive organs. This study aimed to describe the growth of the feathers,
the feather-free body, the reproductive organs and the liver of Dekalb White hens for integration into a
model to determine the daily requirements for lysine (Lys), methionine + cystine (Met+Cys) and threo-
nine (Thr) of a pullet from 1 day old to sexual maturity. Measurements of feather- and feather-free body
protein and, from
15
weeks of age, the ovary, oviduct and liver, were used to describe the growth of
these components using the Gompertz equation. Using the rates of amino acid deposition in each of the
components and assumed efficiencies of utilization of dietary amino acids, the daily amounts of Lys,
Met+Cys and Thr required to sustain this potential growth were calculated. The resultant factorial
model facilitates a more accurate estimate of the daily requirements of growing pullets for Lys, Met+Cys
and Thr based on the growth phase and sexual maturation.
Introduction
Kwakkel
et al
. (1993) applied a model
divided into three, four and five phases and
observed the best fits with the use of four and
five phases. In their four-phase model, 0.69,
0.13, 0.10 and 0.08 of growth occurred in the
first, second, third and fourth phases, re-
spectively, while in their five-stage model,
the first two phases were similar to those in
the four-phase model, while the third, fourth
and fifth phases represented 0.11, 0.03 and 0.04
of growth, respectively. The increase in the
number of phases implies a higher degree of
growth compartmentalization. According to
Kwakkel
et al
. (1993) the essential growth of
the bird (muscles and vital organs) occurs in
Animal growth has long been the subject of
research interest. Early studies (Robertson,
1916; Brody, 1921) suggested that growth
occurs in different cycles during the develop-
ment phase. For birds, three or four cycles of
growth were described, the last of which
occurred at approximately
24
weeks (Brody,
1921). These findings substantiate the multi-
phase growth approach. Grossman and Koops
(1988) have described the growth of laying
hens in three stages: the first stage of growth
accounts for 0.80 of growth, the second for
0.18 and the third for 0.02.
