52 PRINCIPLES OF FEEDING FARM ANIMALS 



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 ration given above : 



0.5 (digestible fat) X 2.25 = 1.13; 



15.0 (digestible carbohydrates 1 ) -j- 1.13 (the carbohydrate equiv- 

 alent of the digestible fat) = 16.13; 



16.13 -f- 2.5 (digestible protein) = 6.5; nutritive ratio, 1 : 6.5. 



In table I in the Appendix, Average Composition and Digesti- 

 bility of American Feeding Stuffs, the sum of the digestible carbo- 

 hydrates and fat is given in the last column, the latter being first 

 changed to its carbohydrate equivalent. The nutritive ratios of 

 the various feeds are, therefore, obtained by dividing this figure 

 by the per cent of digestible protein; e.g., in the case of Green 

 Alfalfa: Digestible protein, 3.6 per cent; digestible carbohydrates 

 and fat, 13.0 per cent; 13,0 -^ 3.6 = 3.6; the Nutritive Eatio, there- 

 fore, is 1 : 3.6. 



The Armsby Standards. The feed requirements for different 

 classes of farm animals, as given by Armsby, show the amounts of 

 digestible true protein and energy values, expressed in therms, 

 that should be supplied daily to growing cattle and sheep at 

 different ages. These figures in all cases include the maintenance 

 requirements for the various animals. 5 



For fairly mature fattening animals (e.g., two- to three-year- 

 old steers) 3.25 therms per pound of gain in live weight are believed 

 to be sufficient, and a similar amount of digestible protein is 

 recommended as in feeding for normal growth. 



The production of a pound of average milk containing about 13 

 per cent solids and 4 per cent fat, will require approximately 0.032 

 pound of digestible protein and 0.27 therm of net energy value in 

 the feed, milk rich in fat and in total solids requiring more than 

 milk containing more water or a lower percentage of fat. Investi- 

 gations by Haecker and by Eckles have furnished additional data 

 on this point (p. 240). 



The method of calculating rations according to the Wolff- 

 Lehmann and the Armsby standards is discussed in Chapter VIII. 



QUESTIONS 



1. What do you understand by the maintenance requirements of animals? 



2. Give maintenance ration for a 1000-pound cow according to (a) the 



WolfF-Lehmann standard, (&) the Armsby standard. 



3. Give the feed requirements for fattening swine according to the WolfF- 



Lehmann standard. 



4. What is meant by nutritive ratio? Give an example. 



5. Show how the feed requirements for a dairy cow are calculated according 



to the Armsby standard. 



5 Farmers' Bui. 346; U. S. De.pt. -Agr. Bui. 459. 



