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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.
 
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