612 
Journal oj Agricultural Research 
Vol. XXIX, No. 12 
greatly affect the level of the plasma 
amino N. 
In Experiment IV the amount of 
protein was reduced without change in 
its quality and without change in the 
energy content of the ration. No 
determinations of the amino N were 
made during the period on an adequate 
ration. The concentration of amino N 
in the blood plasma on the eighth day 
of the second period is decidedly lower 
than the average concentration of 
amino N found in these experiments for 
cows on adequate rations; but this may 
be partly due to the low energy con¬ 
tent of this cow’s ration. (See Table 
I.) 
Fig. 2.—Effect on plasma amino N of an increase of 
75 to 100 per cent in the amount of protein or 50 
per cent in the energy content, or both, in the 
ration of a milking cow after a period on a ration 
inadequate in these constituents. The first 
determinations in this chart show the level of the 
plasma amino N just before the rations were 
increased 
Experiment I.—Amount of energy and pro¬ 
tein in ration increased 
Experiment III.—Amount of protein in¬ 
creased; no change in quality 
Experiment V—Amount and quality of pro¬ 
tein increased 
Experiment VI—Amount and quality of 
protein increased 
Note. —Experiment II does not appear in this 
chart because no determination of amino N was 
made in Experiment II until 21 days after adequacy 
of ration was restored. (See Table V.) 
After the initial drop in plasma 
amino N in Experiments I, III, and IV 
there was a subsequent rise. In Ex¬ 
periment I the plasma amino N on 
May 15 was 1.25 mg. per 100 c. c. On 
the same ration on June 3 and 7 it was 
1.63 and 1.66 mg., respectively, or 32 
per cent higher. In Experiment IV it 
rose from 1.84 mg. on November 13 to 
2.28 mg. on December 9, or 24 per cent. 
The rise in Experiment III was incon¬ 
siderable, 8.7 per cent. 
Figure 2 shows the changes in plasma 
amino N that occurred when the pro¬ 
tein or the protein and energy content 
of the rations were again increased. 
In Experiment III, in which the quan¬ 
tity of the dietary protein was increased 
91 per cent without change in its qual¬ 
ity, there was no change in plasma 
amino N. In Experiments V and VI, 
in which the quality of the dietary 
protein was improved along with a 
similar increase in its quantity (102 per 
cent in the former experiment and 92 
per cent in the latter), the plasma 
amino N actually dropped decidedly. 
In Experiment V it dropped from 2.53 
mg. to 1.81 mg., or 28 per cent, and in 
Experiment VI from 2.28 mg. to 1.9 
mg., or 17 per cent. From these data 
the following conclusions may be 
drawn: 
1. When a milking cow has been on an 
inadequate protein ration for some time y 
the quantity of the dietary protein may 
be increased 90 to 100 per cent without 
causing an increase in plasma amino 
N. The latter may even drop decidedly. 
2. The quality of the dietary proteins 
under certain conditions affects decidedly 
the plasma amino N, and the ration con¬ 
taining the more efficient protein mixture 
is associated with the lower level of 
plasma amino N. 
3. The level of amino N associated 
with a given ration depends largely upon 
the nutritional condition of the animal 
as affected by dietary history . This is 
shown best by comparing periods 1 and 
3 of Experiments I and V (Tables III 
and VII). In period 1 of Experiment 
V the plasma amino N was 2.49 mg. 
In the first determination of period 3 
on the same ration it was 1.81 mg. 
The corresponding data for Experi¬ 
ment I are 2.3 mg. and 1.57 mg., 
respectively. 
When the quantities of the protein 
in the rations in Experiments V and 
VI were increased, at least two factors 
probably contributed to the drop 
in plasma amino N that occurred: 
(1) The improvement in the quality of 
the dietary protein, and (2) the nutri¬ 
tional condition of the animal which 
was produced by the preceding period 
of reduced feeding. 
In Experiment I, in which the energy 
content of the ration was increased 
simultaneously with the quantity of 
protein, the plasma amino N appar¬ 
ently at first did not change. At the 
end of period 2 it was 1.66 mg. Three 
days after the change of ration it was 
1.57 mg. Later it rose to 2.64 mg. 
without further change of ration. The 
increase in the energy content of the 
ration in this experiment much more 
