SELECTION OF RATIONS 295 



tity is an essential consideration, for it is obvious that 

 enough energy and building-material must be supplied 

 to do a given work. It is also obvious that quantity miist 

 be a variable factor according as the animal is large or 

 small, doing hard or light work, giving much or little 

 milk, or fattening rapidly or slowly. 



Account must be made of the proportions of the 

 nutrients, because protein, for instance, has peculiar 

 functions which other nutrients cannot exercise, and 

 less than a certain minimum of the proteins in any given 

 case, would limit production by just the amount of the 

 deficiency. In order for the protein to serve its maxi- 

 mum usefulness, its energy should not be encroached 

 upon to fill a place equally well or better taken by carbo- 

 hydrates; consequently, the proportion of carbohydrates 

 must also be considered. 



393. Nutritive ratio. — ^The relative proportion of the 

 nutrients of a ration is known as the nutritive ratio. By 

 this term is meant the relation in quantity of the digesti- 

 ble protein to all the other digestible organic matter 

 reckoned in terms of carbohydrates. If we multiply the 

 quantity of fat by 2.25 we get its carbohydrate equivalent, 

 and if we add this product to the quantity of diges- 

 tible carbohydrates present we have the carbohydrate 

 value of the digestible matter other than the protein. 

 This sum divided by the number representing the pro- 

 tein gives the nutritive ratio. For instance, in a ration 

 mentioned later there are .94 pound protein, 9.65 pounds 

 carbohydrates, and .49 pound fat. (.49 X2.25 +9.65) h- 

 .94=11.4. 1: 11.4 is therefore the nutritive ratio of the 

 ration. 



A nutritive ratio may be designated as "narrow," 

 "wide," or "medium." These terms do not represent 



