28 
BULLETIN 1281, U. S. DEPARTMENT OF AGRICULTURE 
It will be noted in connection with the data presented in Table 24 
that in summarizing the results of these experiments the net energy 
values given for milk production are based upon the results obtained 
with cow 631. 
It is not impossible, therefore, that the proximity of parturition in 
the latter period contributed a confusing influence in the computation 
of the net energy value for body increase. Judgment as to this 
possibility must await further evidence. 
Since such a material difference has been found to exist between the 
two kinds of production values, it is desired for the present to call 
attention to them by using the terms, " Net energy value of feed for 
body gain" and " Net energy value of feed for milk production." 
Table 24. — Percentage utilization of metabolizable energy available for milk pro- 
duction and the net energy value for milk production 
Cow Xo. 
Period 
Utilization for milk 
production 
Net energy 
for milk 
Interval 
between 
periods 
Usual 
method 
Improved 
method 
631. __ 
Per cent 
f I 1 64.83 
{ II 97. 76 
III i Dry. 
I ; 75.76 
II 68.44 
I III 64.24 
f I 68. 02 
Per cent\ Therms 
81.05 j 1.560 
139. 10 2. 322 
Dry. 0.000 
91.51 I 1.776 
82.43 1 1.699 
76.89 , 1.5S9 
82.48 1-739 
Days 
\ 56 
J 42 
} • 
} « 
615. 
579 
\ II 
69.69 
85.08 
1. <»u 
Such distinction is in keeping with what Armsby has said on the 
subject of milk production, and with the practice of some present- 
day Scandinavian investigators. 
These large differences in the percentage utilization of the available 
metabolizable energy and the net energy of the feed for milk and for 
body gain are evidence suggesting that, when an animal has suffi- 
cient feed, the dry matter of the feed does not first become body tis- 
sue and later milk. It is a process more direct and less expensive. 
"DRYING-UP" PERIOD 
In the computations to obtain the percentage utilization of the 
available metabolizable energy the results derived from experiments 
with the respiration calorimeter were applied, in each case, to the 
average milk and body gain for the digestion period. 
It is not entirely satisfactory to study milk production in a cow 
which is giving less than 1 kilogram of milk in 24 hours. In period 
II, cow 631 though giving only 0.8 kilogram of milk per day was 
treated as in the other milking periods and is included in the above 
table. This period, however, requires a special consideration and 
discussion. During the drying-up period, which is represented by 
the data for cow 631, the percentage of daily decrease in milk pro- 
duction was considerable; and, since the calorimeter work was done 
at the beginning instead of the middle of the period, it is not a true 
representation of the average production during this rapid and con- 
tinuous decrease. If the results obtained with the respiration calori- 
meter are applied to the milk yield of the same day, and the body 
gain corrected in proportion to the milk yield and the body gain of 
