FEEDING FOR MILK 69 



Pounds 



Digestible protein 25 



fat 0.4 



carbohydrates 12.5 



Total dry matter 24. 



Nutritive ratio I to 5.4 



The nutritive ratio means the proportion of nitrogenous to 

 -non-nitrogenous constituents of the food. The protein represents 

 the nitrogenous, and the fat and carbohydrates together represent 

 the non-nitrogenous nutrients, as the food constituents are called. 

 But to put fat on the same basis as carbohydrates, in calculating the 

 nutritive ratio, the percentage of digestible fat is multiplied by 2.25 

 and the result is added to the total of digestible carbohydrates. The 

 reason for this is because fat is thought to have two and one-quarter 

 times the food value of carbohydrates, since a given weight of fat 

 produces two and one-quarter times as much heat in burning as 

 carbohydrates. This method of reasoning is realized, however, to 

 be very imperfect.* In booksf on cattle feeding tables showing the 

 composition of foodstuffs may be found. The carbohydrates are 

 found under the headings Crude Fibre and Nitrogen-Free Extract. 

 There are other tables showing the percentage of digestibility of 

 the fat, protein, crude fibre and nitrogen-free extract in the various 

 fodders. 



By multiplying the amount of any of these constituents in any 

 given fodder by the percentage of the constituent digestible, we get 

 the quantity of the digestible constituent in the fodder. Thus, if we 

 look at a table showing the composition of hay : Average hay we 

 find contains in the 100 lbs. as follows: 9 lbs. protein, 2 lbs. fat, 43 



* The exact nutritive value of fat as compared with carbohydrates is shown 

 by recent experiments to be as follows: 



I gram of carbohydrates = 4180 calories. 

 1 gram of fat = 9400 calories. 



A calorie (small) is that amount of heat required to raise 1 gram of water I de- 

 gree centigrade. Therefore the heat value of fat is about 2.25 times that 

 of carbohydrates, rather than 2.5 times, as has hitherto been accepted- 



t Armsby's " Manual of Cattle Feeding.'' 



