Dec. 1 , 192.5 
1073 
The Maintenance Requirement of Dry Oows 
with the necessary allowances of thermal energy for fat and protein 
gained or lost by the body. 
Considering these factors seriatim, the heat emission by radiation 
and conduction, constituting about 75 per cent of the total heat 
emission, is accurately determined; the estimation of the heat emission 
as latent heat of water vapor somewhat less so. Check tests by 
Armsby and Fries (1 , p. 217-222) place the possible error of this 
latter determination at 6 per cent. This may be taken as the ex¬ 
treme, since the quantity of water vapor liberated in the check tests 
with alcohol is so much smaller than that measured in experiments 
with cows. The influence on the observed heat production of stand¬ 
ing as compared with lying is an important factor. Animals vary 
greatly in the relative time spent standing and lying, and, on account 
of the greater energy cost of maintaining the animal in the standing 
position, it is necessary, in determining net-energy values of feeds 
or net-energy requirements of animals, to eliminate the influence of 
this varible. This point is treated in the discussion following 
Table XIX. 
The influence of refusal of feed on the observed heat production 
is shown by the data for cow 885. The refusal of feed was about at 
a maximum just prior to the measurement of the heat emission in the 
respiration calorimeter. Hence the effect is much magnified. 
The gain or loss of matter by the body influences the heat emission, 
in that heat is required to raise any gain from the temperature of 
the chamber to the temperature of the body; and, conversely, in the 
case of loss of body substance, heat is liberated through the cooling 
of the lost materials from the temperature of the body to that of 
the chamber. 
The thermal environment would of course have a very definite 
influence upon the heat emission, but so long as it is maintained above 
the critical temperature for the subject of the investigation no error 
can be introduced from this source. In practical husbandry, the 
keeping of animals below the critical temperature constitutes a 
special case to which the net-energy values as determined here do 
not apply. It must be kept in mind, however, that the point at 
which physical regulation of body tempetature gives way to chemical 
regulation is not fixed and unvarying, but is affected by the amount 
of the feed eaten. This becomes very important in connection with 
measurements of heat production on submaintenance rations and in 
experiments involving actual fasting. 
In the case of the computed heat production some of the factors 
enumerated as affecting the observed heat production, notably the 
relative time spent standing as compared with lying, the refusal of 
feed, and the thermal environment, also apply. There are, however, 
other factors which affect only the computed heat production. 
These relate principally to the accuracy with which tne heat of 
combustion of the feed and of the excreta is determined. The 
methane produced also becomes a material factor, as do the protein 
and fat gained or lost by the body. These latter considerations 
depend of course on the accurate determination of carbon and nitro¬ 
gen; and the writers in their efforts to account for the difference 
between the observed and computed heat production found that 
very small variations in the carbon estimations are so multiplied 
76649—26f-6 
