614 
Journal of Agricultural Research 
Vol. XXIX, No. 12 
than offset the increased output of 
energy due to the rise in milk yield 
which took place in the third period. 
The data here, therefore, exclude the 
increased energy requirement for the 
increased milk yield in Experiments V 
and VI as a considerable factor tending 
to effect the drop in plasma amino N 
produced by increasing the dietary 
protein. 
F/orn the data in Figures 1 and 2 it 
appears that with milking cows f where 
absorption is a fairly constant and con¬ 
tinuous process , and where there is a 
constant demand for energy for milk 
secretion, the plasma amino N is more 
affected by ( 1 ) the energy content of the 
ration, ( 2 ) the quality of the dietary 
protein, and ( 8) the nutritional condition 
of the animal than it is by the actual 
amount of protein in the ration. In¬ 
creases in the quantity of dietary pro¬ 
tein are not infrequently followed by 
decreases in the concentration of the 
plasma amino N, and it seems a rather 
general rule that a lower level of plasma 
amino N is associated with a higher 
efficiency of the dietary protein for milk 
secretion. 
It must be remembered that all of 
these experiments were made on milk¬ 
ing animals, and it may be pointed out 
that a low plasma amino N associated 
with a high efficiency of dietary protein 
is what one would expect in such ani¬ 
mals on the supposition that the effi¬ 
ciency for milk secretion of the plasma 
mixture of amino acids varies in the 
same direction as the efficiency of the 
dietary protein. When the efficiency 
for milk secretion of the plasma amino 
acid mixture was high, the mammary 
gland would take out a large proportion 
of the total amino N for the synthesis 
of the milk proteins, and less would be 
left in the circulation. The results 
suggest, therefore, that the quality as 
well as the quantity of the plasma 
amino acid mixture is subject to varia¬ 
tion. 
quality of 
Table VIII.— Experiment VI, cow 246. Increase in quantity and 
protein in ration 
Pe¬ 
riod 
No. 
Date 
Milk (daily) 
Amino N * 
Tryptophane 
Yield 
Fat 
Nitrogen 
Blood 
(mg. per 
100 c.c.) 
Plasma 
(mg. per 
100 c.c.) 
Individual 
determina¬ 
tions (mg. per 
100 c.c.) 
Aver¬ 
age 
(mg. 
per 100 
c.c.) 
1922 
Kg. 
P.ct. 
Gm. 
P.ct. 
Gm. 
1 
Dec. 2-8_ 
7. 72 
3.84 
297 
0.546 
42.1 
1 
Dec. 9_ 
7.76 
3.91 
303 
.544 
42.2 
3.93 
2.28 
0.64,0.62 
0.63 
2 
Dsn. 10_ . _ 
j 
2 
Dec. 11_ 
7.98 
3.76 
300 
.554 
44.2 
2 
Dec. 13_ 
8.48 
3.88 
329 
.551 
46.8 
3.93 
1.90 j 
.69, .59 
. 64 
2 
Dec. 14_ 
8. 53 
3.91 
333 
.549 
46.8 
2 
Dec. 15-19_ 
7.64 
4.02 
298 
.569 
42.2 
2 
Dec. 20.. 
7.44 
3.96 
295 
.588 
43.8 
4.01 
2.10 | 
1.01, .96,1.03 
1.00 
2 
! Dec. 22_ 
7.94 
3.97 
315 
.564 
44.8 
3 
Dec. 23-28.. 
7.99 
3.90 
318 
.558 
45.5 
_-___i 
3 
Dec. 29 b . _ 
j 
1923 
j 
3 
Jan. 7__ 1 
7.51 
3.92 
302 
.577 
43.3 
_„| 
3 
Jan 8_ 1 
6. 53 
3.88 
271 
.604 
39.5 
4.06 
2.03 
.65, .62 
.63 
3 
Jan.fl-18. i 
6.73 
4.03 
271 
.607 
40.9 
3 
Jan. 27-Feb. 5...J 
6.62 
4.08 
269 
.600 
39.9 
_| 
3 
Feb. 6 _ 
6.80 
4.00 
272 
.596 
40.6 
4.14 
2.26 | 
.83, .80, .74 
.79 
3 
Feb. 9-15 .i 
6.93 
3.93 
268 
.581 
40.3 
| 
3 
Feb. 16 _! 
7. 35 
4.17 
306 
.614 
45.1 
3.63 
1.98 | 
.95, .86 
.90 
3 
Feb. 18-21 . 
6.89 
4 
Feb. 22-28 _! 
6.81 
| 
4 
Mar. 1-6 _i 
7. 32 
__i 
4 
Mar. 7-12... . : 
7.05 
.I 
4 
Mar. 13_ 
7. 39 
3.83 
2.22 ! 
1. 201,1. 205 
1.20 
° Average difference in duplicate amino-N determinations in blood 4.5 per cent, and in plasma 3.3 per 
cent. 
6 Off feed. Refused 1.66 kg. of grain on Dec. 30; 2.29 kg. of grain on Dec. 31; and 2.37 kg. of grain, 1.18 kg. 
of hay, and 5.91 kg. of silage on Jan. 1. 
