48 FEEDS AND FEEDING 



therms of available energy from the original gross energy of 263.1 

 therms. Of this amount, 118.3 therms were lost in the "work of diges- 

 tion, ' ' leaving 95.6 therms as the net energy value. This could be used 

 for building protein tissues in the body, which would be its highest 

 use, or it could serve for the production of body fat, etc. In the case 

 of the starch, a loss of 18.8 therms occurred in methan and a further loss 

 of 68.7 therms in the "work of digestion," leaving 98.5 therms as the 

 net energy value of 100 Ibs. of digestible starch. 



80. Relative net energy values of concentrates and roughages. Study- 

 ing the data for the typical feeding stuffs, we observe that of the 180.3 

 therms of gross energy furnished by 100 Ibs. of corn meal, 21.2 therms 

 of energy was lost in the undigested matter in the feces, 15.9 therms in 

 methan gas, and 8.1 therms in the waste nitrogenous products excreted 

 in the urine by the kidneys. The sum of these three losses was 45.2 

 therms. All of this was of no value to the animal, but really worse than 

 useless, because work was required in passing this waste material thru 

 the digestive tract and excreting it from the body. Subtracting these 

 losses from the gross energy of the corn meal, there was left 135.1 therms 

 of available energy. Of this available energy, 52.2 therms was lost in 

 the "work of digestion," including masticating and digesting the corn 

 meal and assimilating the digested nutrients. This left 82.9 therms as the 

 net energy value of the 100 Ibs. of corn meal, which could be used for 

 repairing body tissue, for growth, for the formation of body fat, or for 

 the production of external work. 



The last part of the table shows that there was left as net energy only 

 46 per ct. of the original gross energy of the corn meal. While 

 the losses of energy in the case of a rich concentrate are large, they 

 are much greater with the roughages, for the table shows that 100 Ibs. 

 of timothy hay furnished but 43.0 therms of net energy and the same 

 weight of wheat straw only the very small amount of 10.1 therms. 



The cause for the low amount of net energy furnished by the straw is 

 shown clearly in the lower portion of the table. While only 12 per ct. 

 of the gross energy of the corn meal was lost in the undigested matter in 

 the feces, in the case of wheat straw the loss in the feces amounted to 59 

 per ct. Furthermore, the available energy of the corn meal amounted 

 to 75 per ct. of the gross energy, and of this less than two-fifths was 

 lost in the "work of digestion." On the other hand, over four-fifths of 

 the available energy furnished by the wheat straw was lost in this 

 "work of digestion." Because of these losses, only 5 per ct. of the 

 gross energy of the straw was left as net energy, which could be used 

 by the animal for productive purposes. 



The energy used in mastication, digestion, and assimilation is all 

 changed to heat, which can serve to warm the body. Therefore, as is 

 pointed out in the following chapters, such roughages as straw, corn 

 stover, and hay have a much higher relative value for merely maintain- 

 ing animals when considerable heat is needed, as for idle horses in 



