Agriculture Reference
In-Depth Information
strains, the following values were used:
2950 kcal AME n /kg and 210 g CP/kg from
the 1st to the 6th week; 2850 kcal AME n /kg
and 170 g CP/kg from the 7th to the 12th
week; and 2750 kcal AME n /kg and 160 g CP/
kg from the 13th to the 18th week.
Every week, the birds were weighed and
sample animals were selected for slaughter
based on the average weight of each experi-
mental unit. After a fasting period of 24 h the
sampled birds were individually weighed
and euthanized using CO 2 , and feather sam-
ples were collected. The weight of feathers
was determined by the difference between
the weight of the fasted bird and the weight
of the defeathered carcass.
The defeathered carcasses were ground
to obtain homogeneous samples. An aliquot
of each sample was set aside for subsequent
pre-drying. The samples were then ground in
a micro-mill and analysed for nitrogen con-
tent (Kjeldahl method, crude protein = nitro-
gen × 6.25), ether extract (petroleum ether in
Soxhlet equipment), dry matter (oven at
105°C) and ash (muffle at 550°C). The feather
samples were chopped with scissors and sub-
jected to the same chemical analyses.
To describe the growth of the major body
components, the Gompertz function was used
(Gompertz, 1825).
Wt = Wm × e { - e [ - B × ( t - t *) ]}
Allometric coefficients were obtained
from the relationship between the natural
logarithm (ln) of the chemical component
weights (ln Cq ): protein, water, lipid and ash
as a function of the natural logarithm of the
protein weight (ln BP ), according to the fol-
lowing equation:
ln  Cq = a + b  × ln  BP
The feathering factor ( FFc ) was calculated as
described by Gous et al . (1999), considering
the relationship of the weight at maturity ( Wm )
of the feathers ( FW ) and body protein ( BP ).
FFc = 0.84 × FWm / BPm 2/ 3
Results
Growth of the body
The results presented here describe the growth
potential of broiler and laying strains in
terms of body weight, feather weight and
chemical composition. The parameters of the
Gompertz function fitted for each genotype
have biological meaning and therefore allow
comparisons to be made between the growth
parameters of each strain and sex. Table 18.1
shows the values of empty body weight (EBW)
and empty feather-free weight (EFFW) for
each strain.
The parameter Wm for EBW of males
and females differed by approximately 2.08 kg.
Females were smaller; however, the param-
eters B and t* indicate that their growth was
more precocious than that of males. The
broiler lines can be ranked by precocity in
the following order: CF, RF, CM and RM, with
maximum weight gain ( WGmax ) occurring
at 28, 35, 35 and 42 days, respectively.
For the laying strains, the brown (HLB
and HSB) and white (HLW and HSW) strains
showed distinct patterns of growth. Based on
Wm , white strains were lighter by approxi-
mately 0.5 kg or 0.75 relative to the brown
strains. The parameter B is related to early
growth and consequently to a decrease in
the time required to reach sexual maturity.
The HLW strain showed higher B and t* val-
ues compared to the other strains for both
EBW and EFFW. No differences were ob-
Where t is the age in days; Wt is the weight at
time t , kg; Wm is the weight at maturity, kg;
B is the rate of maturing per day; t* is the age
at which the growth rate peaks, days; and e is
the numerical base of Euler .
The absolute growth rate ( dW / dt ) and
weight gain or deposition of various chem-
ical components (g/day) can be calculated
using the following equation:
dW / dt = B × Wt × ln( Wm / Wt )
The absolute growth rate increases until it
reaches a maximum rate, at which point Wt
is 0.368 of Wm and t coincides with t* . After
this age, growth rate decreases as Wt ap-
proaches Wm .
Considering B , Wm and the numerical
base e , the maximum rate of deposition
( dW / dtmax ) is calculated to be dW / dtmax = B
× Wm / e , in kg/day. The maximum weight
( Wmax ) is Wmax = Wm / e .
 
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