SELECTION OF RATIONS 297 



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 we must take 

 into account the composition and digestibility of the 

 particular feeding-stuffs which enter into a ration, if we 

 would discover what it really is supplying of available 

 food compounds. It is evident that usually feeders can- 

 not have their cattle foods analyzed, and so they must 

 resort to the tables of composition and digestibility, 

 which are, or may be, in the hands of every farmer. 



395. Calculation of digestible nutrients. — 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 species, stage of growth and 

 conditions of curing, and an average percentage of pro- 

 tein or an average coefficient of digestibility is likely to 

 differ widely from the actual facts as pertaining to a 

 particular material. All that can be done is to select as 

 nearly as possible the figures which have been found for 

 feeding-stuffs in the condition of those which are to be 

 fed. If the hay is from matiu-e grass, use the composi- 

 tion percentages and digestion coefficients given for 

 such hay; if the silage is from mature corn, pursue a 

 similar course in this case, and so on. Difficulty may be 

 met in finding suitable figures, because tables of com- 

 position and digestibility are not fully developed and 

 classified on the basis of the character of the materials. 



The assumed ration which we wish to discuss con- 

 sists of: 



