MEASURING THE USEFULNESS OP FEEDS 41 



Table II. Likewise there are 70.9 Ibs. of nitrogen-free extract, 94 per ct. 

 of which is digestible. Multiplying in each case and adding the products, 

 we have 67.8 Ibs. as the " digestible carbohydrates." 



It will be noted that the typical feeds presented in this table show 

 wide differences in the amounts of different digestible nutrients they 

 furnish. Corn and wheat are high in digestible carbohydrates and 

 rather low in digestible protein, while wheat bran and linseed meal are 

 high in digestible protein but low in digestible carbohydrates. Linseed 

 meal contains more digestible protein and less than one-fourth as much 

 digestible fat as the flax seed from which it comes. The roughages range 

 lower in digestible nutrients than the concentrates. Oat straw is es- 

 pecially low in digestible protein, while immature and actively growing; 

 pasture grass will contain nearly as much digestible protein as wheat 

 bran, if cut and dried to the same water content. 



70. Nutritive ratio. As protein serves special uses in the body, in 

 discussions of feeding stuffs and rations the term nutritive ratio is used 

 to show the proportion of digestible protein contained in comparison 

 with the other nutrients. 



The nutritive ratio of any feed is the proportion, or ratio, between the 

 digestible crude protein and the combined digestible carbohydrates and 

 fat. It should be noted especially that the nutritive ratio is based on 

 the digestible and not the total nutrients, and furthermore that it is 

 based on digestible crude protein and not digestible protein. 



The nutritive ratio of a feed is computed in the following manner: 

 The digestible fat in 100 Ibs. of the given feed is multiplied by 2.25, 

 because fat will produce 2.25 times as much heat on being burned in 

 the body as do the carbohydrates. The product is then added to the 

 digestible carbohydrates and the sum is divided by the amount of 

 digestible crude protein, the quotient being the second factor of the 

 ratio. The nutritive ratio of dent corn is computed as follows : 



Second factor/)! 

 Diges. fat Heat equiv. Diges. carbohydrates nutritive ratio 



(4.6 X 2.25) + 67.8 



10.4 



7.5 



Diges. crude protein 



Nutritive ratios are expressed with the colon, thus, 1 :10.4. The nutri- 

 tive ratio of dent corn is therefore 1 : 10.4 (read 1 to 10.4) ; i. e., for each 

 pound of digestible crude protein in corn there are 10.4 Ibs. of digestible 

 carbohydrates or fat equivalent. A feed or ration having much crude 

 protein in proportion to carbohydrates and fat combined is said to have 

 a narrow nutritive ratio; if the reverse, it has a wide nutritive ratio. 

 Oat straw has the extremely wide nutritive ratio of 1:44.6, because of 

 its low content of digestible protein compared with the carbohydrates 

 and fat ; oats the medium one of 1 :6.3 ; and protein-rich linseed meal the 

 very narrow ratio of 1:1.6, the carbohydrates and fat being less than 

 twice the crude protein. 



