SELECTION OF RATIONS 303 



generously meet the demands of the class of animals for 

 which they are designed. 



400. Earlier protein standards revised. — ^Through more 

 recent investigations, revisions of the earlier protein 

 standards have been recommended. These are in gen- 

 eral in the direction of a lower minimum of protein, and 

 the data secured seem to justify the change. At the same 

 time, care should be taken in not fixing the protein mini- 

 mum too low, partly because a generous protein-supply 

 promotes the general welfare of the animal, and partly 

 because of the variable eflBciency of the single proteins 

 which are found in the different feeding-stuffs in greatly 

 unlike proportions. The amoimt of protein fed in a given 

 case should be such as to guarantee a sufficient amount 

 for the actual constructive work demanded. (See Par. 275.) 

 Probably with certain feeding-stuffs the minimimi might 

 be lower than with others. It is very evident then that 

 the protein-supply in feeding formulas for production 

 cannot safely be resolved to the exact limitation pf the 

 nitrogen compounds needed. The standards that have 

 been suggested will be considered in the following pages. 



401. Presence of growth-promoting bodies. — ^The dis- 

 covery of growth-promoting bodies attached to cattle 

 foods (see Par. 278) leads to the conclusion that rations 

 should be selected under certain conditions with refer- 

 ence to the presence of these essential compounds. This 

 is especially true where animals are likely to be fed on a 

 restricted diet, as, for instance, swine, or where by- 

 product feeds are used the treatment of which may have 

 removed part or all of the food accessories. With animals 

 eating the forage portion of plants in large quantities, 

 such as the bovines, there is little danger that there will 

 be a deficiency in the food of these essential compounds. 



