406 
Journal oj Agricultural Research 
Vol. XXX, No. 5 
SUMMARY OF DIRECT AND INDI¬ 
RECT HEAT ESTIMATION 
The results of the study of the de¬ 
tails of direct and indirect calorimetry 
in experiments with steers and cows at 
this institute may be summarized as 
follows: 
The direct heat measurement is in 
general more accurate than the balance 
method of indirect heat computation. 
The direct method, therefore, serves as 
a valuable check on the accuracy of the 
analytical work involved in the indi¬ 
rect method. 
In the measurement of the nutritive 
values of feeds, however, the direct 
and the indirect methods are about 
equally accurate, and the latter is much 
the more easily accomplished. 
One source of error, not affecting 
direct heat measurement, but involved 
in the utilization of both direct and 
indirect heat measurements in the de¬ 
termination of the net energy values of 
feeds, is the loss of moisture of feeds 
and feces during grinding preparatory 
to analysis, but this factor affects both 
methods. 
The most important source of error 
affecting direct and indirect calorim¬ 
etry in different ways is loss of matter, 
from the urine and feces, presumably 
through fermentation, during drying, 
preliminary to the determination of 
energy by means of the bomb calorim¬ 
eter. 
This loss, which contains carbon and 
nitrogen, is an important factor in the 
computation of the heat production by 
the indirect method, and in the appli¬ 
cation of the results of the direct 
method in determining the net energy 
value of feeds. 
This loss of matter affects th§ esti¬ 
mation of (a) metabolizable energy, as 
determined by subtracting from the 
energy of the feed the energy of the 
excreta, (6) heat production, as deter¬ 
mined by subtracting from the metab¬ 
olizable energy the energy of the 
gain (carbon and nitrogen balances 
multiplied by factors), (c) energy of 
gain, as determined by subtracting 
from the metabolizable energy the di¬ 
rectly observed heat production. 
The determination of the energy of 
the gain from the nitrogen and carbon 
balances does not involve the loss under 
discussion, since the nitrogen and the 
carbon can be determined on the fresh 
substance. When, how r ever, the direct 
heat estimation is used in the final 
computation of net energy any such 
advantage as might accrue from the 
greater accuracy of this direct heat 
estimation is lost through the fact that 
in order to derive the amount of the 
energy of the gain, which is a factor of 
the net energy estimation, the directly 
observed heat production must be 
subtracted from the metabolizable 
energy, this last datum being directly 
affected by the loss in drying of the 
excreta. 
In those cases in which there is a 
gain of body tissues, or no appreciable 
loss, the error due to possible change in 
glycogen content of the body may be 
considered as negligible, and the esti¬ 
mation of the gain in energy, by the 
indirect method, may be as accurate as 
when determined by the direct method. 
On account of the possibilities of 
change in the glycogen content of the 
bodies of cows, in connection with 
milk production, the chances for error 
in indirect calorimetry with cows seem 
greater than witn steers. 
There is need for careful control of 
the conditions of drying feces and 
urine, and of a thorough investigation 
into the composition and nature of the 
substances lost, in order to make pos¬ 
sible the more accurate estimation of 
the dry matter and the energy of these 
excreta. 
LITERATURE CITED 
(1) Armsby, H. P., and Fries, J. A. 
1903. THE AVAILABLE ENERGY OF TIMOTHY HAY. 
INVESTIGATIONS WITH THE RESPIRATION CALO¬ 
RIMETER. U. S. Dept. Agr., Bur. Anim. 
Indus. Bui. 51, 77 p., illus. 
( 2 ) - 
1903. THE PRINCIPLES OF ANIMAL NUTRITION. 
WITH SPECIAL REFERENCE TO THE NUTRITION 
OF farm animals. 614 p., illus. New York 
and London. 
(3) - 
1904. THE RESPIRATION CALORIMETER AT THE 
PENNSYLVANIA EXPERIMENT STATION. Exp. 
Sta. Rec. 15: 1037-1050, illus. 
(4) - 
1908. INVESTIGATIONS IN ANIMAL NUTRITION. U. 
S. Dept. Agr., Bur. Anim. Ind. Ann. Rpt. 
(1906) 23: 263-285, illus. 
(5) -and Fries, J. A. 
1911. THE INFLUENCE OF TYPE AND OF AGE UPON 
THE UTILIZATION OF FEED BY CATTLE. TJ. S. 
Dept. Agr., Bur. Anim. Ind. Bui. 128, 245 p., 
illus. 
( 6 ) - 
1913. A COMPARISON OF THE OBSERVED AND COM¬ 
PUTED HEAT PRODUCTION OF CATTLE. Jour. 
Amer. Chem. Soc. 35: 1794-1800. 
(7) Kellner, O., and Kohler, A. 
1900. UNTERSUCHUNGEN tlBER DEN STOFF- UND 
ENERGIE-UMSATZ DES ERWACHSENEN RINDES 
BEI ERHALTUNGS- UND PRODUKTIONSFUTTER. 
Landw. Vers. Stat. 53: 1-474. 
(8) Kriss, M. 
1921. OBSERVATIONS ON THE BODY TEMPERATURE 
of dry cows. Jour. Agr. Research 21: 1-28, 
illus. 
(9) Lavoisier, [A. L.l, and Laplace, [P. S.] 
1784. memoire sur la chaleur. Hist. Acad. 
Roy. Sci. [Paris] 1780: 355-408, illus. 
(10) Rubner, M. 
1894. DIE QUELLE DER THIERISCHEN WARME. 
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