EXERCISE 86 



COMPUTING THE NUTRITIVE RATIO OF STOCK FEEDS 



Statement. The successful stockman gives his animals feeds containing protein and carbohy- 

 drates in the proportions in which they require these materials for their best development, just 

 as the skilled mechanic mixes sand and cement in the proper ratio to make good concrete. The ratio 

 between the digestible protein and digestible carbohydrates in a foodstuff is called the nutritive ratio 

 of that material. 



Object. To determine the nutritive ratio of feeds and to compare different feeds as to their value 

 in compounding rations. 



Materials. Pencil and paper, and tables giving the composition of feeding stuffs. (See Appendix, 

 Table I.) 



Directions. In computing the nutritive ratio only the digestible portion is usually considered. 

 Included in the carbohydrates are the starch, sugar, crude fiber, and fat. As the fat contains about two 

 and one fourth times as much energy as starch or sugar, the amount of digestible fat in the feeding 

 stuff is multiplied by two and one fourth before it is added to the other carbohydrates. This process 

 is termed converting fat into carbohydrate or starch equivalent. The nutritive ratio is obtained by 

 dividing the per cent of total digestible carbohydrates by the per cent of digestible protein contained 

 in the foodstuff. In stating the nutritive ratio the protein is expressed as i and the carbohydrates as 

 the quotient obtained. As an example, corn (according to Table I, Appendix) contains 7.5 per cent of 

 digestible protein, 67.8 per cent of digestible carbohydrates, aside from fat, and 4.6 per cent of fat. 

 Multiplying the fat by 2j (4.6 X 2j) and adding the product (10.4) to the carbohydrates (67.8), we 

 have as the total carbohydrates 78.2. Dividing this amount (78.2) by the amount of protein (7.5), we 

 have as the quotient 10.4. Thus the nutritive ratio of corn is one part digestible protein to 10.4 parts 

 digestible carbohydrates, written 1 : 10.4. This means that for every pound of digestible protein in 

 corn there are 10.4 pounds of digestible carbohydrates. Feeds in which the difference between the 

 amount of protein and carbohydrates is small are said to have a narrow nutritive ratio, as 1 : 3, while 

 those feeds in which the difference is large, as in the case of corn, are said to have a wide ratio. 



The importance of such a calculation is based on the fundamental principle that no other 

 constituent of feeds can take the place of protein in forming new tissue or replacing old, or in 

 making milk, eggs, wool, feathers, etc. Therefore we must begin the building of a ration with a 

 certain minimum of protein. It is true that there are three sources of carbohydrates, fat, starch 

 and sugar, and crude fiber. For the purposes of calculating the nutritive ratio we convert these 

 values into that of carbohydrates, but later we shall learn that they have widely different values. 



Problems. Compute the nutritive ratio of each of the following feeds and classify them as narrow, 

 medium, and wide. Cottonseed meal, linseed meal, wheat, bran, wheat middlings, oats, kafir grain, alfalfa 

 hay, clover hay, cowpea hay, corn silage, wheat straw, and corn stover. (See Appendix, Table I.) 



Questions. What are the principal uses which the animal makes of protein ? What common food- 

 stuffs supply protein most abundantly? What are the principal sources of protein in your locality? 

 What are the principal uses to which animals put carbohydrates ? What are the principal sources of 

 carbohydrates in your neighborhood? What are some of the foodstuffs in your neighborhood which 

 have a narrow nutritive ratio? Name six feeds possessing a wide nutritive ratio. Name some of the 

 common feeds which have a medium nutritive ratio. 



References. Plumb, C. S. Beginnings in Animal Husbandry, p. 272. Webb Publishing Company. 

 Henry and Morrison. Feeds and Feeding Abridged, pp. 37-38. The Henry Morrison Company. Jordan, 

 W. H. The Feeding of Animals, p. 283. The Macmillan Company. Harper, M. W. Animal Husbandry for 

 Schools, p. 359. The Macmillan Company. 



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