428 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



animal on a heavy ration may be so excessive that differences in 

 the thermal energy of feeds may have no significance, an animal 

 on a small or maintenance ration, may be able to utilize the 

 thermal energy. 



The use of the productive value of a feed is no doubt a decided 

 advance in the science of animal nutrition, as it emphasizes the 

 differences in the productive values of the digested nutrients of 

 different classes of feeds. It is clear that the digested nitrogen- 

 free extract, for example, of hays and fodders, does not have the 

 same value to the animal as that of grains and other concentrates. 



The value of a feed for nutrition is thus indicated by : 



1 i ) Its content of digestible protein, or power to produce flesh. 



(2) Its productive value in terms of fat, or its power to pro- 

 duce fat. 



Mineral Materials. Animals require inorganic as well as 

 organic materials. 1 The term "inorganic" is not strictly accurate 

 when used in connection with phosphates, as the phosphorus is 

 partly in organic combination. However, any addition of phos- 

 phates to the ration is made as inorganic substances. Ash is left 

 by all organs of the body when burned, and mineral matter ap- 

 pears essential to their proper growth and development. Mineral 

 substances are required in processes of digestion and metabolism. 

 Animals fed on food from which the ash has beeen extracted be- 

 come irritable, nervous, show weakness of the extremities, and 

 die sooner than if not fed at all. 



The most important inorganic substances are salt, phosphoric 

 acid, and lime. Salt is found in the digestive juices. In moderate 

 amounts, it appears to favor the retention of proteids by the 

 body. Cattle of average weight should receive 20 to 25 grams; 

 sheep and pigs, 4 to 8 grams; and horses, 15 to 25 grams per day. 

 With heavy rations of difficulty digestible foods, cattle may re- 

 ceive as much as 80 grams; sheep, 12 grams; and pigs, 15 grams 

 per day. An excess of salt increases the consumption of water, 

 and is undesirable. It is best to mix the salt with the food. 

 1 See Ohio Bulletin No. 207. 



