Models of Growth under Nutrient Limiting Conditions
131
size. These curves are in good agreement with the observed growth performance of rats and dogs fed different diets; some predicted and observed
values for dogs are shown in Figure 3.
400
E
0>
:c
g' 200
~
>u
o
m
100
200
Age in days
300
400
Fig. 2. Predicted growth curves of rats fed diets containing different percentages
of utilisable protein
10
0>
-x
L
OJ
(jj
5
3
>CJ
0
m
P8=
9---t5 12.o%
~
o
~
~
...-.!-._6.o%
...........
.............
o
/""
o
/ .
9
./""rk1=400
...........
k2=150
100
200
Age in days
300
400
Fig. 3. Predicted curves, and measured body weights, of litter mate Beagle dogs
fed diets containing 12.0 or 6.0 per cent of utilisable protein
These equations exhibit many of the features required for a successful
model of the growth of animals.
1. The age-weight curves in Figure 2 illustrate an early self-accelerating
phase and a self-inhibiting approach to an asymptotic adult value.
2. The point of inflection, representing the transition between these
phases, occurs at between 1/3 and 1/4 adult size.
3. The model also shows the effect of a limiting amount of dietary protein on both growth velocity and maximum body size.
4. The equations predict a constant relationship between the maximum
body weights of different species and the times required to reach a given
9*