Agriculture Reference
In-Depth Information
Fig. 2.4.
Screenshot of InraPorc illustrating the change in the SID threonine to lysine requirement ratio in
the growing pig between
30
and 115 kg of body weight.
constant. However, there are indications that
this is not the case and that amino acid com-
position of whole-body protein can be af-
fected by various conditions, including the
amino acid supply (Conde-Aguilera
et al
.,
2010). In the first version of InraPorc, we de-
termined a much lower efficiency for Ile than
for Val and Leu (i.e. 0.60, 0.76 and 0.71, re-
spectively) even though the three branched-
chain amino acids are catabolized by the same
enzyme complex. Subsequent experimental
work in our group indicated the SID Ile:Lys
requirement ratio was overestimated result-
ing in an underestimation of the maximum
efficiency. We thus changed the maximum ef-
ficiency of Ile utilization from 0.60 to 0.67 in
a more recent version of the software. It is
striking that the maximum efficiencies of Trp
and Met+Cys are low compared with that of
Lys. As for Ile, it is possible that the SID Trp:Lys
and (Met+Cys):Lys requirement ratios have
been overestimated. However, differences in
the efficiency of amino acid utilization can-
not be excluded and the reasons for these dif-
ferences need further research.
The concept of using a fixed value for the
maximum efficiency of amino acid utilization
results in the relationship between the de-
position and the supply of a limiting amino
acid (above maintenance) being described
by a linear-plateau function, which intersects
the origin, and where the slope of the linear
line segment corresponds to the maximum
efficiency. This differs from the way we
described the relationship between protein
deposition and energy intake (i.e. curvilinear-
plateau function). The linear-plateau function
for this type of response has been criticized
because the animal may adapt its efficiency
depending on the supply of a limiting nutri-
ent. Also, even if the linear-plateau function
were to be accurate for a single animal, a
curvilinear-response would be observed for a
group of animals (Pomar
et al
., 2003). In the
future, we may change the way we describe
the response to the amino acid supply.
A curvilinear-plateau function may have ap-
pealing properties, although the efficiency with
which essential amino acids can be used for
amino acid deposition cannot exceed 100%.
