Calculation of Standard Rations 285 



composition oH the ration into conformity with the 

 standard selected. 



As a means of showing the steps involved in cal- 

 culating what a ration is, and how to improve it if 

 necessary, we will assume that it is desired to learn 

 whether a food mixture which a milch cow is eating 

 is what it should be, and if it is not, how to make 

 it so. The standard ration for a 1,000-pound cow, 

 giving twenty -two pounds of average milk, expressed 

 in terms of water -free nutrients, has been given in 

 the preceding table. 



The first point which requires our attention is that 

 this standard is mainly expressed in terms of water - 

 free digestible nutrients. This means that Ave must 

 take into account the composition and digestibility of 

 the particular feeding stuffs which enter into a ration 

 if we would discover w^iat it really is supplying of 

 available food compounds. It is evident that usually 

 feeders cannot have their cattle foods analyzed, and 

 so they must resort to the tables of averages of com- 

 position and digestibility, which are, or may be, in the 

 hands of every farmer. But what figures shall be 

 selected for use ? As we have learned, feeding stuffs, 

 especially fodders, differ within quite wide limits in 

 what they contain and in what the animal will dissolve 

 from them, according to the stage of growth and con- 

 ditions of curing, etc., and an average percentage ^of 

 protein or an average coefficient of digestibility is 

 likely to differ widely from the actual facts as per- 

 taining to a particular material. All that can be 

 done is to select as nearly as possible the figures which 



