38 FEEDS AND FEEDING, ABRIDGED 



show the proportion of digestible protein they contain. By nutritive 

 ratio is meant the ratio which exists in any given feeding stuff between 

 the digestible crude protein and the combined digestible carbohydrates 

 and fat. It is determined in the following manner : The digestible 

 fat in 100 lbs. 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 carbo- 

 hydrates and the sum is divided by the amount of digestible crude 

 protein, the quotient being the second term of the ratio. The manner 

 of computing the nutritive ratio of dent corn is as follows : 



Second term of 

 Diges. fat Heat equiv. Diges. carbohy. nutritive ratio 



(4.6 X 2.25) + 67.8 _ 1Q4 



7.5 

 Diges. crude protein 



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

 nutritive 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 lbs. 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 nutri- 

 tive 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 being 

 less than twice the crude protein. 



When the total digestible nutrients (including fat X 2.25) in a feed 

 or ration are given, as in Appendix Table III and the preceding table, 

 the nutritive ratio may be computed by simply subtracting the diges- 

 tible crude protein from the total digestible nutrients, and dividing 

 the remainder by the digestible crude protein. For example, the 

 nutritive ratio of dent corn is found thus : (85.7 — 7.5) -e- 7.5 = 10.4, 

 second term of nutritive ratio. 



The term carbonaceous feed is a convenient designation for a feed- 

 ing stuff having a wide nutritive ratio. Similarly, the term nitro- 

 genous feed designates a feeding stuff having a narrow nutritive ratio. 



II. The Energy of Food 



Tables of digestible nutrients tell what part of the food may be 

 digested and absorbed, and thus really enter the body of the animal, 

 but they throw no light on the use made of the nutrients when once 

 they are within the body. To obtain such information the respira- 

 tion apparatus and the respiration calorimeter have been devised. 



