Agriculture Reference
In-Depth Information
advances in age (Gous
et al
., 1999) and al-
lows for a more precise estimation of the
nutritional requirements.
Although there was already a mathemat-
ical description of growth (Winsor, 1932) a
new method was introduced in the 1980s
(Emmans, 1981) that integrated growth with
factorial models to calculate the nutritional
requirements of the bird. Protein is used to
define the genetic potential for growth and, in
the growth model of Emmans (1981), it is the
preferred variable to be used in the factorial
model to predict maintenance requirements
and the requirement for growth, as there is a
close relationship between protein and the
other physical and chemical components of
the bird. Therefore, the first step in estimating
the nutritional requirements of a growing bird
is to describe the potential growth of protein,
which has traditionally been determined us-
ing the Gompertz function (Gous
et al
., 1999).
The parameters of the Gompertz equation:
the mature protein weight, rate of maturing
and
t
*, the age when protein deposition is
greatest, can be used to differentiate between
genotypes together with knowledge of the
ratio of lipid to protein in the mature bird
(Hancock
et al
., 1995). These parameters,
which are subject to genetic selection, influ-
ence the energy and amino acid requirements
needed to achieve the bird's genetic potential
(Gous
et al
., 1999).
Taking into account the proposal of Em-
mans (1981) for the application of factorial
models, it is necessary to know the potential
for growth and nutrient deposition in the
body. Based on this approach, the Laboratory
of Poultry Science of UNESP-Jaboticabal has
developed models to predict the energy
(Sakomura
et al
., 2011) and amino acid re-
quirements (Siqueira
et al
., 2011) of growing
chickens. Studies were carried out to deter-
mine the growth parameters of two broiler
and four laying strains raised in Brazil, and
these are presented in this review.
Veterinary Sciences, UNESP-Jaboticabal, São
Paulo, Brazil. The genetic parameters of two
broiler strains and four laying strains were
characterized. The broiler strains included
Ross 308
®
and Cobb 500
®
, and both sexes were
studied. In this study, 1920 broiler chicks were
separated into four groups with four replicates
of
120
birds each, resulting in
16
experimental
units. The birds were housed in pens with wood
shavings as litter at a density of
10
birds/m².
The groups consisted of Ross 308 males (RM)
and females (RF), Cobb 500 males (CM) and
females (CF). The experimental period was 56
days.
The laying strains studied included
Hy-Line Brown (HLB), Hisex Brown (HSB),
Hy-Line White W-
36
(HLW) and Hisex White
(HSW) strains, and only pullets were evalu-
ated in this case. Three hundred chicks of
each strain were housed first in brooding
cages (1st to 6th week) and then rearing
cages (7th to 18th week). These birds were
divided into four groups, each with four
replicates of
75
birds, resulting in
16
experi-
mental units. The experimental period was
126 days.
The broiler strains were fed diets based
on maize and soybean meal to meet their nu-
tritional requirements, following the breed-
ers' recommendations for the strains during
each phase of development. The levels of me-
tabolizable energy (AME
n
) and crude protein
(CP) were: 3010 kcal AME
n
/kg and
220
g
CP/kg from the 1st to the 7th day; 3150 kcal
AME
n
/kg and
215
g CP/kg from the 8th to the
28th day; 3200 kcal AME
n
/kg and
200
g CP/kg
from the 29th to the 49th day; and 3245 kcal
AME
n
/kg and
180
g CP/kg from the 50th to
the 56th day.
The laying strains were fed diets based
on maize, soybean meal and wheat bran to
meet their nutritional requirements, follow-
ing the recommendations of Rostagno
et al
.
(2005) for each phase of development. The
lightweight strains were given the following
levels of metabolizable energy (AME
n
) and
crude protein (CP): 2950 kcal AME
n
/kg and
210
g CP/kg from the 1st to the 6th week;
2850 kcal AME
n
/kg and
180
g CP/kg from
the 7th to the 12th week; and 2800 kcal
AME
n
/kg and
160
g CP/kg from the 13th to
the 18th week. For the semi-heavy weight
Materials and Methods
The studies were conducted in the Laboratory
of Poultry Science, Faculty of Agriculture and
