Agriculture Reference
In-Depth Information
in the model. The model is described by
Eqn 16.3:
AAI
= [(
AAm
c
×
BPm
0.73
×
u
)
+ (
FPL
×
FP
×
AA
f
)] + [(
AA
c
×
PD
c
)/
k
+ (
AA
f
×
PD
f
)/
k
+
AA
c
× (
PD
Ova
+
PD
Ovi
+
PD
Liv
)/
k
] (16.3)
Where
AAI
is the digestible amino acid
requirement (mg/day);
AAm
c
is the amino
acid requirement for the maintenance of
feather-free body protein (mg ×
BPm
0.73
×
u
);
BPm
0.73
is the metabolic body protein weight
at maturity (kg);
u
is the degree of maturity
of feather-free body protein (
u
=
BPt
/
BPm
);
FPL
is the feather protein loss (0.04 g/day);
FP
or
FPc
is the feather protein weight (g/day);
AAf
is the amino acid content of feather pro-
tein (mg/g);
AA
c
is the amino acid content of
feather-free body protein (mg/g);
PD
c
is the
rate of deposition of feather-free body (g/day);
PD
f
is the rate of protein deposition in the
feathers (g/day);
PD
Ova
is the rate of protein
deposition in the ovary (g/day);
PD
Ovi
is
the rate of protein deposition in the oviduct
(g/day);
PD
Liv
is the rate of protein deposition
in the liver (g/day); and
k
is the efficiency
of utilization of amino acid for protein de-
position.
Laying hens lose a significant amount
of feathers during growth (Silva, 2012). The
daily loss of feathers may be regarded as the
maintenance requirement for feathers, as sug-
gested by Emmans (1989). The amino acid
composition for feather protein maintenance
was considered to be equal to its concentra-
tion in feather protein.
Coefficients for calculating the mainten-
ance requirements of the feather-free body
for Lys, Met+Cys and Thr were obtained from
studies conducted at UNESP-Jaboticabal. The
Lys requirement was calculated as
174
mg
×
BPm
0.73
×
u
(Siqueira
et al
., 2011), the co-
efficient for Met+Cys requirement was 93.5
and for Thr, 44.7 (Bonato
et al
., 2011).
The coefficient used to describe the ef-
ficiency of utilization of Lys (
k
Lys
), Met+Cys
(
k
Met+Cys
) and Thr (
k
Thr
) was 0.80 for all three
amino acids.
The contents of Lys, Met+Cys and Thr
in feathers and in the feather-free body were
measured by Silva (2012) to be 18.7 mg/g,
89.2 mg/g and 44.3 mg/g protein, respectively,
in feathers (
AA
f
) and 67.8 mg/g, 33.3 mg/g and
40.4 mg/g, respectively, in the feather-free
body (
AA
c
).
Estimating the requirements
The Lys, Met+Cys and Thr requirements were
estimated by applying the parameters for
Dekalb White hens using the Martin
et al
.
(1994) model (Model 1) and then making
corrections for feather growth and the inclu-
sion of organs (Model 2).
Model
1:
based on Martin
et al
. (1994)
(M1):
AAI
= [(
AAm
c
×
BPm
0.73
×
u
)
+ (
FPL
×
FP
×
AA
f
)]
+ [(
AA
c
×
PD
c
)/
k
+ (
AA
f
×
PD
f
)/
k
]
(16.4)
Model
2:
corrected for feather loss and the
growth of reproductive organs and liver (M2):
AAI
= [(
AAm
c
×
BPm
0.73
×
u
)
+ (
FPL
×
FP
×
AA
f
)]
+ [(
AA
c
×
PD
c
)/
k
+ (
AA
f
×
PD
f
)/
k
+
AA
c
× (
PD
Ova
+
PD
Ovi
+
PD
Liv
)/
k
] (16.5)
Results
Description of the growth parameters
The growth parameters for the protein weights
of feathers, feather-free body and ovary, ovi-
duct and liver of Dekalb White hens are given
in
Table 16.1
.
At maturity (
Pm
) the total pro-
tein weight of the bird was 382 g. Of this, 0.57
corresponded to the feather-free body, 0.35
to feathers, 0.03 to the ovary, 0.03 to the oviduct
and 0.02 to the liver.
The correction for feather loss applied
to the observed weights resulted in a 4% in-
crease in the protein weight of feathers (
PFm
;
Table 16.1
). This correction enabled an ap-
proximation to be made of the real feather
weight, which is of considerable importance
when determining the amount of each amino
acid required for the growth of feathers, espe-
cially cystine.