14 
BULLETIN 1281, U. S. DEPARTMENT OF AGRICULTURE 
Since in the work reported methane is quantitatively determined, 
whereas the values for carbon dioxide and heat of fermentation are 
estimated, the digestibility of the rations in this experiment has been 
computed, (1) on the usual basis of feed constituents minus feces 
constituents, (2) by considering methane as indigestible, and (3) by 
taking account also of loss of feed energy through the heat of fermenta- 
tion. The digestion coefficients as computed by the three methods 
can be compared by reference to Table 9. 
In the preparation of Table 9 the factors used and the method of 
computation were as follows: 
1 liter of methane — 0.7168 grams. 
1 liter of carbon dioxide — 1.9652 grams. 
Ratio of methane to carbon dioxide (in fermentation gases) 1: 3.2. 
Scheme of computation: 
Grams methane liters methane liters of carbon dioxide 
equivalent to the carbon dioxide of fermentation, or grams methane X 
17,546 — calories due to fermentation grams carbon dioxide 
energy equivalent (calories). 
Table 9. — Apparent digestibility of dry matter in terms of energy, computed by 
three different methods 
Period 
Coefficients computed by 
three methods 
Dry matter digested per day as 
energy — 
Cow No. 
1 
Feed 
minus 
feces 
2 
CH 4 
added 
to feces 
3 
CH t and 
heat of 
fermenta- 
tion 
added 
to feces 
Method 1 
Method 3 
Esti- 
mated 
heat of 
fermenta- 
tion 
631 
| if:::::: 
llll 
| if:::::: 
llll 
«::::::: 
Per cent 
66.67 
65.93 
66.75 
65.99 
66.84 
66.62 
68.83 
68.32 
Per cent 
58.57 
58.14 
59.24 
58.81 
59.60 
59.25 
61.23 
60.61 
Per cent 
47.92 
47.89 
49.35 
49.38 
50.07 
49.56 
51.25 
50.48 
Calories 
21, 642. 
21, 338. 
21,488.7 
22, 114. 
22, 331. 
22, 207. 
25, 303. 6 
25, 135. 9 
Calories 
15, 558. 4 
15, 498. 6 
15, 887. 6 
16, 547. 6 
16, 728. 9 
16, 519. 6 
18, 840. 5 
18, 572. 7 
Calories 
3, 455. 6 
3, 316. 9 
615 
3. 181. 5 
3,161.8 
3. 182. 2 
579 
3, 231. 1 
3, 671. 2 
3, 728. 
In Table 9 are found side by side two columns (the sixth and 
seventh from the left) giving the dry matter digested per day ex- 
pressed in terms of energy and computed according to the old and 
new methods, also one column giving the daily estimated heat of 
fermentation for each period. Comparing methods 1 and 3 the 
digestible dry matter, as energy, is from 16.61 to 18.75 per cent 
less when the nonusable energy of methane and of heat of fermen- 
tation is classed with that left in the feces. 
THE RESPIRATORY GASES 
The respiratory products and gases from all sources are mixed in 
the outcoming air. The methane as determined comes presumably 
from a single source; but the carbon dioxide comes from various 
sources and can not be separated according: to origin, the total carbon 
dioxide therefore representing the metabolism of the cow, of the 
bacteria of her alimentary tract, and of the man engaged in milking. 
CORRECTION FOR MILKER 
In respiration-calorimeter experiments with milking cows it is 
necessary that a man enter the apparatus to do the milking; hence 
a correction must be applied to the heat emission, and to the water 
and carbon dioxide as measured. A determination made at the 
