38 



PRINCIPLES OF FEEDING FARM ANIMALS 



mann standards become very simple and are as easily applied as any 

 standard so far proposed for farm animals. 



The nutritive ratio of a feed (or a ration) is the proportion 

 between the digestible protein and the sum of the digestible carbo- 

 hydrates and fat contained therein. The fat is changed to its 

 carbohydrate equivalent by multiplying with 2.25, because it has 

 2.25 times as high heat value as similar amounts of carbohydrates. 

 For example, the nutritive ratio is expressed as 1 : 6.5, meaning that 

 there are 6.5 pounds digestible carbohydrates and fat combined 

 for every pound of digestible protein. The nutritive ratio is cal- 

 culated as follows, e.g., in the case of the first ratio given above : 



0.5 (digestible fat) X 2.25 = 1.13; 



15.0 (digestible carbohydrates) +1.13 (the carbohydrate equiv- 

 alent of the digestible fat) = 16.13 ; 



16.13 -h 2.5 (digestible protein) = 6.5. 



The nutritive ratio of the ration for milch cows given is figured 

 in the same way, as follows : 

 .5 X 2.25 = 1.13 ; 



13.0 +1.13 = 14.13; 



14.13 -^ 2.5 = 5.7; the nutritive ratio is, therefore, 1 : 5.7. 



The Armsby Standards. The estimated feed requirements for 

 different classes of farm animals according to Armsby are given in 

 the following table ; the figures show the amounts of digestible true 

 protein and energy values, expressed in therms, that should be sup- 

 plied daily to growing cattle and sheep at different ages. These 

 figures in all cases include the maintenance requirements for the 

 various animals. 5 



Estimated Feed Requirements per Day and per Head (including the Maintenance 

 Requirements) . Armsby. 



5 Farmers' Bulletin 346. 



