Agriculture Reference
In-Depth Information
otherwise, body protein deposition (
PD
)
will be lower than
pPD
.
influenced by nutritional and environmen-
tal factors and current body status. The
compensatory response will be determined
by adding
dLD
to the difference between
current lipid mass and
dLt
:
LD = dLD +
(
dLt - Lt
) (g/day)
Feather Protein Deposition Potential
Feathers make up a large proportion of the
chicken's body, and its amino acid re-
quirements differ from those of the rest of
the body. The potential for feather protein
deposition (
pPDf
) is defined by genotype
and can also be described by a Gompertz
function:
The concept of maintaining a desired lipid
composition will allow the bird to use its
body reserves at any time to supply its en-
ergy requirements when the feed contains
excesses of all essential nutrients other than
energy.
pPDf
=
Bf
×
Pft
× ln(
Pmf
/
Pft
) (g/day)
Where
Pft
is the feather protein content at a
determined point in time (g),
Pmf
is feather
protein content at maturity (g) and
Bf
is fea-
ther protein maturity rate.
Water and Ash Deposition
Under non-limiting conditions, the rela-
tionship between ash and water does not
vary much between sexes or among geno-
types (Gous
et al
., 1999). Therefore, the
deposition of ash (
AD
) and water (
WD
) is
described in the model by an allometric
ratio to protein.
AD
= Exp(
aA
+
bA
× Log(
P
) (g/day)
Body Lipid Deposition Potential
Lipid deposition in poultry is influenced by
dietary composition. Therefore, in order to
estimate the desired lipid deposition, its
ratio to protein deposition potential should
be established (Emmans, 1981). This allows
the desired lipid composition of a specific
genotype to be estimated.
The best way of describing the desired
lipid deposition or lipid body composition
relative to body protein is based on lipid:
protein ratio at maturity (
LPm
), and during
growth, using an allometric coefficient of
lipid content relative to protein (Emmans
and Kyriazakis, 1999). The desired lipid
composition (
dLt
) in the model at a deter-
mined point in time is estimated as:
WD
= Exp(
aW
+
bW
× Log(
P
) (g/day)
All the parameters required to describe spe-
cific genetic strains were obtained from
studies conducted at the Poultry Science
Laboratory of FCAV at UNESP-Jaboticabal
and are presented in
Table 14.1
.
Estimate of Current Status
Empty body weight gain (
EBWG
, that is, carcass
with feathers and no gut fill) on a given day is
calculated as the sum of five components.
dLt
=
LPm
×
Pm
× (
Pt
/
Pm
)
b
1
(g/day)
Where:
EBWG
=
PD
+
LD
+
WD
+
AD
+
PDf
(g/day)
This gain is added to empty body weight on
the previous day to determine current body
weight.
EBWG
is divided by the values that rep-
resent the ratio of the gastrointestinal tract
(
GIT
) to whole body weight (5%, according
to Lopez
et al
., 2007) in order to estimate
average daily gain (
ADG
).
b
1 = 1.46 ×
LPm
0.23
Thus, desired daily lipid deposition (
dLD
)
can be estimated as:
dLD
=
pPD
×
LPm
×
b
1 × (
Pt
/
Pm
)
b
1 -
1
(g/day)
When
dLt
is estimated, compensatory gain
may be identified, as lipid deposition is
EBWG
=
ADG
×
1/
GIT
(g/day)
