24 
BULLETIN 1281, U. S. DEPARTMENT OF AGRICULTURE 
The heat production as computed and as measured by the respira- 
tion calorimeter is arranged for comparison in Table 20. The com- 
puted is also expressed in per cent of the observed. 
THE OBSERVED AND COMPUTED HEAT PRODUCTION 
The fairly close agreement between the computed and the observed 
heat production may be taken as a measure of the degree of accuracy 
to be expected from experiments on milk cows in a respiration 
chamber, using a bomb calorimeter for determining the energy of 
feed and excreta. 
In period III, cow 631, the heat measurement was adversely 
affected by the presence of an excess of air in the absorber water, 
and hence the heat for certain periods of time could not be measured. 
From the other main portion of the day the total heat for the 24 
hours was computed by applying to the missing smaller sections the 
average heat per minute, as observed during standing and lying. 
This, of course, increases the possibility of error. However, the 
comparison with the computed heat production proves it to have 
been very small. 
It will be noted that the computed heat production is, in seven 
cases out of eight, not more than 3.5 per cent greater than the ob- 
served heat production. In the nature of the case, this difference 
covers a considerable number and diversity of errors, all presumably 
slight. It appears that the true value lies above the observed, and 
that the computed values are therefore less in excess of the actual 
than is suggested by a statement of the computed as per cent of the 
observed. In the opinion of the writers the determination of heat 
production by indirect calorimetry is sufficiently accurate for pur- 
poses of research in the feeding of farm animals. 
Table 20. — Observed and computed heat production 
Cow No. 
Period 
Heat production 
Computed 
in per 
Observed 
Computed 
cent of 
observed 
631 
( I 
i n 
in 
f i 
i n 
I in 
{ ii 
Calories 
11, 463. 9 
12, 333. 9 
13,219.2 
11,435.5 
12, 137. 3 
12, 032. 2 
13, 235. 6 
12, 896. 2 
Calories 
11, 720. 5 
12, 598. 8 
13, 680. 3 
11,756.5 
12, 286. 2 
12, 747. 6 
13, 545. 9 
13, 165. 5 
Per cent 
102. 24 
102. 15 
615 
103. 49 
102. 80 
101. 23 
579 
105. 95 
102. 34 
102.09 
NET ENERGY OF FEED FOR BODY GAIN AND MILK PRODUCTION 
Before taking up the question of standing and lying it is desirable 
to determine the percentage utilization of the available metabolizable 
energy for body gain and also for milk production, using the computed 
heat values. 3 Cow 631 offers an excellent opportunity for such a 
comparative study. She was in full milk during one period, was 
almost dry in the second, and fully dry in the third period, whereas 
the ration remained the same throughout all the periods. This 
animal was standing during less time than she was lying, but the 
3 In the following computations the data for the observed heat production have not been used, but are 
reserved pending the solution of a problem as to method of use. 
