MILK PRODUCTION AND BODY INCREASE OF DAIRY COWS 
Table 8. — Daily production of methane 
13 
Period 
Combustible gases 
CH4 computed from com- 
bustible gaseous carbon 
Cow No. 
Per 100 
COj by 
Carbon 
grams 
Energy 
com- 
equiva- 
Total 
digestible 
equiv- 
bustion 
alent 
carbo- 
hydrates 
alent 
Grams 
Grams 
Grams 
Grams 
Calories 
f I 
540.45 
147. 38 
196. 94 
5.36 
2, 627. 97 
631 
11 
518. 77 
141. 46 
189. 04 
5.23 
2, 522. 55 
I HI 
497. 61 
135. 70 
181. 32 
5.02 
2, 419. 53 
f I 
494. 50 
134. 85 
180. 20 
4.84 
2, 404. 59 
615... 
11 
497. 69 
135. 72 
181. 36 
4.81 
2, 420. 07 
I HI 
505. 37 
137. 82 
184. 15 
4.96 
2, 457. 30 
579 
{ A 
574. 20 
156. 58 
209. 23 
4.90 
2, 791. 96 
583. 08 
159. 00 
212. 47 
5.06 
2, 835. 20 
APPARENT DIGESTIBILTIY OF RATIONS BY IMPROVED METHOD 
The digestible portion of a feeding stuff is that portion which in 
passing through the alimentary tract is resorbed, and thereby 
becomes available for the maintenance of the functions of the 
organism. 
►ecause of the difficulty of determining true digestibility, however, 
it has been customary to ascribe to a feed a much higher digestibility 
than it really has; for, by using the prevailing method of computation 
which assumes that feed constituents minus feces constituents equal 
digestible constituents, a part of the feed which is neither resorbable 
nor useful is included with the digestible. It is a well-known fact 
that ordinary feeding stuffs for cattle contain ingredients which 
would be altogether useless for the support of the vital functions of 
the animal organisms were it not for the presence and activity of 
microorganisms in the alimentary tract. Although because of such 
activity, a certain amount of material is converted into substances 
useful to the body, a considerable part of the original feed substance is 
changed into forms which can not support the physiological require- 
ments of the animal. It has been customary to consider these useless 
substances as digestible matter. This gives too high a figure for 
apparent digestibility. Since the quantity of methane and its equi- 
valent energy can be determined, and since the heat of fermentation 
of the organisms which liberate the methane can be estimated with 
a fair degree of accuracy, it is possible to exclude these factors from 
considerations of apparent digestibility, thus arriving at a closer 
approximation of true digestibility. 
In Table 5 only the visible portions of the excreta have been con- 
sidered. However, the excreted useless portion of the feed contains 
gases as well as solids. It is therefore consistent to include the useless 
gases with the feces and compute the digestibility as has been sug- 
gested (Fries) (3) by using the following values : Methane, equivalent 
to 13,344 calories per gram; ratio of methane to carbon dioxid in the 
products of fermentation in the alimentary tract, 1 to 3.2 by volume; 
and heat of fermentation equal to 2,000 calories per gram of carbon 
dioxide produced. The apparent digestibility thus computed will 
approach the metabolizable and the net values, and hence will be a 
more accurate expression of nutritive value than will a figure derived, 
as usual, by a method which fails to consider the important factor of 
gaseous losses. 
