40 FEEDS AND FEEDING, ABRIDGED 



13 lbs. of carbon and the steer voids 12.25 lbs. during the day in the 

 feces and urine, and in the carbon dioxid in the air breathed out of 

 the lungs, then 0.75 lb. of carbon must have been stored in his body. 

 Some of this will be in the protein tissues built during the day, while 

 the remainder will have been stored as fat. Thru such trials scientists 

 have been able, in some measure, to tell what becomes of the food 

 animals consume. 



The respiration calorimeter. — A still more accurate means of 

 measuring the usefulness of feeds is furnished by the respiration 

 calorimeter. This is an improved and exceedingly complicated form 

 of the respiration apparatus, in which not only the feces, urine, and 

 gaseous waste products can be collected, but in which the heat given 

 off by the animal can also be accurately measured. By means of 

 this apparatus, it is possible to find exactly how much of the energy 

 or fuel value of the feed the animal has been able to use in growth, 

 fattening, or work. The first and only respiration calorimeter built 

 in this country for carrying on experiments with large animals 

 was erected by Armsby at the Pennsylvania Station some years 

 ago. 



Fuel value of feeds. — A mature animal may be compared to a 

 steam engine, in which a part of the power derived from the fuel is 

 used for the operation of the engine itself, while the surplus may 

 perform useful work. The steam engine derives its energy from coal 

 or wood ; the animal, from the feed it consumes. Both re(iuire a 

 small amount of repair material — steel, brass, etc., for the engine, and 

 protein and mineral matter for the animal — but the largest demand 

 with engine and mature animal alike is for fuel. It is therefore both 

 important and interesting to consider the relative value of feeds in 

 terms of the fuel they can furnish the body. 



The value of any feeding stuff as fuel for the animal depends on 

 the amount of energy which it will furnish when burned. As with 

 coal, the fuel value of a feed is determined by burning a weighed 

 quantity of it in pure oxygen gas under pressure in an apparatus 

 called a calorimeter. The heat given off is taken up by water 

 surrounding the burning chamber and is measured with a ther- 

 mometer, the units of measure employed being the Calorie and the 

 therm. 



A Calorie (C.) is the amount of heat required to raise the tem- 

 perature of 1 kilogram of water 1° C, or 1 lb. of water nearly 4° F. 

 A therm (T.) is 1,000 Calories. 



The fuel value of 100 lbs. of various substances, or the heat evolved 

 on burning them, is as follows: 



