48 ■ Feeds and Feeding. 



The heat or chemical energy evolved on burning 100 lbs. of vari- 

 ous substances is as follows : 



Therms. 

 Anthracite coal 358.3 



Timothy hay, containing 15 per ct. moisture 175.1 



Oat straw, containing 15 per ct. moisture 171.0 



Corn meal, containing 15 per ct. moisture 170.9 



Linseed meal, containing 15 per ct. moisture 196,7 



Pure digestible protein . 186.0 



Pure digestible carbohydrates 186.0 



Pure digestible fat 422.0 



The table shows that, on burning, 100 lbs. of anthracite coal 

 yields 358.3 therms, or enough heat to raise the temperature of 

 358,300 lbs. of water 4° F., or about 8000 lbs. of water from 32° F., 

 or freezing, to 212° F., or boiling temperature. One hundred 

 pounds of timothy hay likewise burned would yield 175.1 therms, 

 or about half that of coal. Linseed meal has a higher fuel value 

 than corn meal because it contains more oil. Digestible protein 

 yields about the same amount of heat as the carbohydrates and fat 

 more than twice as much. In comparing feeding stuffs the diges- 

 tible fat is regarded as having 2,25 times the fuel value of the di- 

 gestible carbohydrates, (131) 



The energy evolved on burning a substance may be expressed by 

 the work it will do in lifting a weight, the foot-ton being the unit 

 of such measurement. A Calorie will furnish the energy required 

 to raise a weight of 1,53 tons 1 foot, A therm is the energy re- 

 quired to raise a weight of 1530 tons 1 ft., or 1 ton 1530 feet. 



IV. The Energy of Food. 



69. Available energy. — The fuel value of any food does not 

 necessarily measure its nutritive value to the animal, because foods 

 containing the same heat units may vary in the amount of avail- 

 able energy which they can furnish to the body. This is because : 



1. A part of the food passes thru the alimentary tract un- 

 digested. 



2. The carbohydrates, especially the woody fiber, undergo fer- 

 mentations in the intestines and paunch, gases being evolved which 

 are without fuel value to the animal. 



3. When the protein substances in the body are broken down 

 they form urea, a nitrogenous compound which escapes thru the 

 kidneys. Urea has fuel value which is lost to the body. 



