30 BULLETIN 1281, U. S. DEPARTMENT OF AGRICULTURE 
be higher than the average for the same body weight if the animal 
were not pregnant. If this is the correct interpretation, then the 
period in question also indicates that the estimated heat of fer- 
mentation used in the "improved method "of computing the metab- 
olizable energy is not far from the correct value. 
The above observations as to the increased maintenance require- 
ment during pregnancy in the cow are readily understood in the 
light of the finding by Magnus-Levy (9) of a steady increase of 
oxygen requirement throughout the course of pregnancy in woman, 
the conclusion of Murlin (10) that the extra metabolism of the 
pregnant female dog, as related to reproduction activity, is propor- 
tional to the weight of the puppies at birth, and the findings of 
Carpenter and Murlin (11), in a study of metabolism in three pregnant 
women, that the difference in heat production per hour, before and 
after parturition, was very nearly the same as that of the newborn 
infant, and that the rate of metabolism of the infant was 2.6 times 
that of the mother, in terms of calories per kilogram of body weight. 
EFFECT OF ADVANCE IN LACTATION 
Eliminating cow 631, which was studied during only one period 
in which milk was produced in any considerable quantity, the effect 
of advance in lactation on utilization of the available energy for milk 
production with the other two cows can be studied (Table 22). 
Cow 615, whose tests extended over a period of 94 days, offers the 
best opportunity for study. With this cow there was a decrease 
in the percentage utilization of the available energy for milk produc- 
tion in each period. With cow 579, which had been in milk about 
three months at the time of the first period, there was a slight increase 
in percentage utilization during the second period. Hence no definite 
conclusion can be drawn from this experiment so far as the effect 
of the advance of lactation on the percentage utilization of the avail- 
able metabolizable energy for milk production is concerned, and the 
accumulation of additional data must be awaited. 
STANDING AND LYING 
The results of nutrition investigations, in order to be comparable, 
must represent certain uniform experimental conditions, any variations 
from which must be taken into account in the application of the con- 
clusions. Thus it is customary to compute the experimental results 
obtained with animals of different weights so as to apply to animals 
of standard weights, usually either 1,000 pounds or 500 kilograms 
live weight. Also it is understood that feeding standards apply 
exactly only under conditions essentially the same as those under 
which they have been established, which in connection with this 
study means comfortable stable conditions and from which it follows 
that allowance should be made in the application of the conclusions 
and of all feeding standards for any considerable departure from the 
basic conditions implied. 
Earlier experiments on steers with the respiration calorimeter 
established the fact that irrespective of the kind or quantity of feed 
eaten there is always a large percentage difference in the amount of 
heat given off by the animal according to its position in regard to 
standing and lying. Although the animal in the course of the day 
in these experiments always gave off more heat per minute while 
standing than while lying, as the data accumulated it was noticed 
