Availahle Energy 163 



The heat vahies of a gram of the dry substance 

 of various cattle foods, which is a mixture of the 

 several nutrients, was found by recent determinations 

 to be the following, expressed in small calories: 



cal. cal. 



Mixed hay 4494 Corn meal 4471 



Alfalfa hay 4478 Linseed meal 5040 



Oat straw 4480 Flaxseed meal 6935 



Sugar beets 3931 Kice meal 4400 



These figures mean that when a gram of each of 

 these materials is wholly burned the heat produced is 

 as stated. 



Availahle energy. — We must distinguish, however, 

 between the heat produced when any food substance is 

 wholly oxidized in a calorimeter and the heat or energy 

 which is available when the same material is applied to 

 physiological uses. It never happens that the combus- 

 tible portion of a ration is entirely burned in the animal. 



In the first place, the food of domestic animals is 

 practically never all digested and, as only the digested 

 portion furnishes energy, the available fuel value of a 

 ration must be based primarily, not upon the total 

 quantity of dry matter it represents, but upon the 

 amount which is dissolved and passes into the blood. 

 If all feeding stuffs or rations were digested in the 

 same proportion and with the same ease, their total 

 fuel values might show their relative energy worth, but 

 as digestion coefficients for dry matter vary from less 

 than 50 per cent with the straws to nearly 90 per cent 

 with some of the cereal products, it is evident that the 

 fuel waste in the feces is not uniform. 



