MEASURING THE USEFULNESS OF FEEDS 45 



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, or gross energy, is determined by burning a weighed 

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

 a caloritneter. The heat given off is taken up by water surrounding 

 the chamber in which the material is burned and is measured with a 

 thermometer, the units employed being the Calorie and the therm. 



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

 of 1 kilogram of water 1C., or 1 Ib. of water nearly 4F. 



A therm (T.) is 1,000 Calories, or the amount of heat required to 

 raise 1,000 kilograms of water 1C., or 1,000 Ibs. of water nearly 4F. 



The gross energy of 100 Ibs. of various substances, or the heat evolved 

 on burning them, is approximately as follows: 



Therms 



Anthracite coal 358.3 



Corn meal, average water content 180.3 



Linseed meal, average water content 210.3 



Timothy hay, average water content 181.2 



Wheat straw, average water content 184.6 



Pure digestible protein 263.1 



Pure digestible carbohydrates 186.0 



Pure digestible fat 422.0 



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

 358.3 therms, or enough heat to raise the temperature of 358,300 Ibs. 

 of water 4 F., or about 8,000 Ibs. of water from 32 F., or freezing, 

 to 212 F., or boiling temperature. One hundred pounds of corn 

 meal likewise burned yields 180.3 therms, or about half as much as 

 coal. Linseed meal furnishes more gross energy than corn meal because 

 it contains more fat. Roughages, such as timothy hay and wheat straw, 

 yield just as much gross energy as a concentrate like corn meal. 

 Digestible protein yields considerably more heat than the carbohydrates, 

 and fat over twice as much as the carbohydrates. 



77. Available energy. The gross energy of any feed does not neces- 

 sarily measure its nutritive value to the animal, because feeds which 

 yield the same number of heat units in the calorimeter may vary in 

 the amount of energy they actually furnish the body. This is because : 



1. A part of the food is not digested, but is voided in the feces. This 

 may be compared to bits of coal dropping thru the grate of the boiler 

 unturned. 



2. The carbohydrates, especially woody fiber, undergo fermentations 

 in the paunch and large intestine with the formation of combustible 

 gases, chiefly methan, which are without fuel value to the animal. (48) 

 Even in well-constructed engines a similar loss of energy occurs in the 

 combustible gases which escape thru the chimney without being burned. 



3. Some of the protein substances digested and absorbed from the 

 feed are broken down in the body with the formation of urea and 

 other nitrogenous waste compounds, which are excreted by the kidneys. 



