MEASURING THE USEFULNESS OF FEEDS 41 



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 263.1 



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. One hundred pounds of timothy hay likewise burned 

 yields 175.1 therms, or about half as much as coal. Linseed meal 

 has a higher fuel value than corn meal because it contains more oil. 

 Digestible protein yields considerably more heat than the carbo- 

 hydrates, and fat over twice as much as the carbohydrates. 



Available energy. — The fuel value of any feed does not necessarily 

 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 available energy which they can furnish to the body. This 

 is because: 



1. A part of the food consumed passes thru the alimentary tract 

 undigested. This may be compared to bits of coal dropping thru the 

 grate of the boiler unburned. 



2. The carbohydrates, especially woody fiber, undergo fermenta- 

 tions in the intestines and paunch, combustible gases, especially 

 methane or marsh gas, being formed, which are without fuel value to 

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

 occurs in the combustible gases which escape thru the chimney with- 

 out being burned. 



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

 form urea, a nitrogenous compound which is excreted by the kidneys. 

 Urea has fuel value which is lost to the body. Again we may liken 

 this loss to that which occurs in the boiler thru the creosote which, 

 tho having fuel value, is not burned in the fire box but escapes or is 

 deposited in the chimney. 



The fuel value of an}'' food which remains after deducting these 

 three losses represents the available energy of the food. This is the 

 portion which the animal can use for body purposes. 



Net energ-y. — The available energy of the food measures its value 

 for heat production in the animal, but does not represent its true 

 value for other purposes. The animal must spend a part of the total 

 available energy of any food in the work of masticating and digest- 



