Agriculture Reference
In-Depth Information
analysed diet composition. A feed rationing
plan is used to indicate how much feed is
provided to the animal. This can be based
on fixed quantities or as a percentage of the
ad libitum
feed intake.
In a single simulation, the information
from the animal profile, the feed sequence
plan and the feed rationing plan are com-
bined and the user can evaluate the re-
sponse in various ways (see the figures used
later in the text). It is beyond the scope of
this chapter to depict all the graphs and re-
ports that can be produced; however, we are
of the view that InraPorc is a very appropri-
ate tool for professional nutritionists and to
teach swine nutrition. It deals with prac-
tical aspects such as the dynamics of feed
intake, growth and nutrient requirements. It
can be used to study nutrient partitioning
and to illustrate the different concepts used
in energy and amino acid nutrition (e.g. ex-
plaining the difference between GE, DE, ME
and NE). Apart from running a single simu-
lation, comparisons of simulations can be
performed by combining different modules.
For example, two different feed rationing
plans can be used to evaluate the conse-
quence of applying a feed restriction during
the finisher phase. Also, sensitivity ana-
lyses can be performed to evaluate the sen-
sitivity of model predictions to parameters
of the animal profile or to the supply of the
most important nutrients.
maintain a body weight of 5 kg for
1
year.
In these restricted pigs, the oxygen con-
sumption reflects the maintenance energy
requirement and was, as anticipated, con-
siderably lower in the restricted pigs com-
pared to the normally fed pigs of a similar
body weight during the first months of the
experiment (McCance and Mount, 1960).
However, it increased during the course of
the feed restriction to attain values similar
to that of the control group after 12 months
of feed restriction. This indicates that it is
very difficult to measure the maintenance
energy requirement in growing animals
and to give it a biological meaning. As van
Milgen and Noblet (1999) wrote: 'The con-
cept of maintenance may not be appropriate
for growing animals. However, no suitable
alternatives are currently available, and it
may be better to fully adhere to the concept
of maintenance and accept its constraints.'
In InraPorc, many concepts are ex-
pressed relative to maintenance. Apart from
the lack of suitable alternatives, we also felt
that maintenance (or homeostasis) is a fun-
damental concept in biology. In non- producing,
mature animals energy intake equals energy
production. If this were not the case, energy
would be gained or lost. Non-producing
animals regulate energy intake, energy pro-
duction or both to maintain energy equilib-
rium. Even in obese humans, energy intake
is only slightly greater than the energy ex-
penditure. The difference is typically less
than 0.5% but if maintained for a long period
of time it results eventually in obesity. In an
experimental setting, we would consider
the 0.5% difference as a 'margin of error', but
it clearly indicates that energy intake and en-
ergy expenditure are highly regulated, even
in the case of obesity.
Our Love-Hate Relationship
with Maintenance
The concept of maintenance is widely used
in animal nutrition. Virtually all nutrition-
ists have some feeling as to what mainten-
ance is. However, there has been quite some
debate on how maintenance should be in-
terpreted for growing animals. The main-
tenance energy requirement corresponds to
the situation where energy intake equals en-
ergy expenditure. For a growing animal, it is
clear that this situation is not attained be-
cause energy intake exceeds energy expend-
iture, which consequently results in energy
gain and growth. Lister and McCance (1967)
offered feed to piglets so that they would
Feed Intake
In the first version of the InraPorc software
tool, we proposed three equations to ex-
press
ad libitum
feeding or energy intake
relative to body weight. These included a
linear function (
Y
=
a
+
b
×
BW
), an asymp-
totic function (
Y
=
a
× (
1
- exp(-
b
×
BW
))),
and a power function (
Y
=
a
×
BW
b
). We had
