Agriculture Reference
In-Depth Information
energy during growth and thus for the avail-
able energy for protein and lipid deposition.
For the same energy expenditure at 60 kg
body weight, using 0.75 as a scalar under-
estimates the energy expenditure by 15% at
20 kg (relative to using 0.60 as a scalar) and
overestimates it by 11% at 120 kg.
In InraPorc, the maintenance energy
requirement is determined based on the
fasting heat production and 'normal' phys-
ical activity. The fasting heat production is a
function of body weight raised to the power
0.60 and feed intake before fasting. There
are several studies showing that the fasting
heat production is affected by the feeding
level before fasting (Koong
et al
., 1982; de
Lange
et al
., 2006).This relationship is some-
what in contradiction with the classical sep-
aration of requirements for maintenance and
growth, because it implies that the mainten-
ance requirement depends on the level of
feed intake and thus on growth.
The change in the maintenance energy
requirement during growth (as a function
of feed intake and body weight) is converted
to a default value of 100% in InraPorc.
We opted for this approach because it is
virtually impossible for users to appreciate
quantitatively the different components of
maintenance (e.g. changes in physical ac-
tivity, breed differences and immune func-
tion). As lipid deposition is considered an
energy sink, a change in the maintenance
energy requirement will affect predictions
for lipid deposition and traits related to
lipid deposition such as backfat thickness.
We do not recommend that the user changes
the maintenance energy requirement based
on predictions and measurements of back-
fat thickness. Lipids in backfat account for
not more than 18% of the total body lipids
(Kloareg
et al
., 2006) and only the thick-
ness of this tissue is determined during
growth or at slaughter. In InraPorc, backfat
thickness is predicted from the lipid mass
(the equation is given in the configuration
window and can be changed by the user).
Because of the difficulty in actually meas-
uring whole-body lipid deposition, we rec-
ommend that the user changes the predic-
tion equation for backfat thickness if a
systematic bias in the prediction of backfat
thickness is observed, rather than adjust-
ing the maintenance energy requirement
for the animal.
Response to a Feed Restriction
As indicated by Whittemore and Fawcett
(1976), a restriction in energy intake may not
only affect lipid deposition, but can also
affect protein deposition. A linear-plateau
model has often been used to model the rela-
tionship between energy intake and protein
deposition. With increasing energy intake,
protein deposition increases up to a max-
imum (referred to as PDmax). An increase in
energy intake beyond that required to attain
PDmax will not affect protein deposition
and the additional energy will be used for
lipid deposition only. In InraPorc, we used a
curvilinear plateau function to describe the
response of protein deposition to energy in-
take. Also here, we used maintenance as a
reference criterion and we expressed the NE
intake as multiples of maintenance. The rea-
son for this is that we felt that a
1-
MJ change
in energy intake has a different meaning for
a very young pig than a
1-
MJ change in an
older pig. Consequently, energy itself is not
used as the 'currency', but it is scaled rela-
tive to maintenance.
Figure 2.1
is a screen-
shot from the InraPorc software and illus-
trates how we represent the response of
the response of the pig at 75 days of age is
represented (the cursor below the graph
allows the changing of the age of the pig).
At 75 days of age, this pig eats 2.28 times the
NE requirement for maintenance, resulting
in a protein deposition of 107.5 g/day and a
lipid deposition of 105.9 g/day. It is clear
that at 75 days of age, the animal is in the
energy-dependent phase of the response, as
a change in energy intake would affect both
protein deposition and lipid deposition.
The pigs would need to eat 2.79 times the
NE requirement for maintenance to attain
is beyond the feed intake capacity of the ani-
mal at this stage. With increasing body
weight, the feed intake capacity of the pig
