FEEDS AND FEEDING 33 



ducer or as an energy and fat producer, i. e. } it is the ratio of digestible 

 crude protein to digestible carbohydrates and fat in the feed or ration. 

 Inasmuch as fat is two and one-quarter times as valuable as carbohydrates, 

 the amount of digestible fat is multiplied by two and one-quarter and added 

 to the amount of digestible carbohydrates. The sum is then divided by 

 the amount of digestible protein. The first term of the ratio is always 

 "1," while the second term is obtained by the following formula: 



digestible carbohydrates + 2^ X digestible fat = gec(md tmn of ^ ^ 

 digestible protein 



The nutritive ratio is written as "1 : 6" or "1 : 14," or whatever it 

 may be. It is read as "one to six," or "one to fourteen," Thus one finds 

 the nutritive ratio of corn as follows: from Table I it is found that 100 

 pounds of corn contain 7.8 pounds of digestible protein, 66.8 pounds of 

 digestible carbohydrates and 4.3 pounds of digestible fat. Then, substi- 

 tuting in the above formula: 



66.8 + 2^ X 4.3 = 9 g 



7.o 



Therefore, the nutritive ratio of corn is 1 : 9.8. The nutritive ratio 

 of a ration containing two or more feeds may be calculated in a similar 

 manner. 



Ordinarily, a nutritive ratio of 1 : 6 or less is called a narrow ratio; 

 i. e., the feeding-stuff or ration contains a relatively large amount of pro- 

 tein and a relatively small amount of carbohydrates and fat. A ratio of 

 1 : 7 to 1 : 9 is called a medium ratio; i. e., there is present a medium 

 amount of protein and a medium amount of carbohydrates and fat. A 

 ratio of 1 : 10 or greater is called a wide ratio; i. e., the proportion of pro- 

 tein to carbohydrates and fats is relatively small. 



The Energy Values of Feeding-stuffs. One of the functions of the 

 ration of an animal is to act as a source of energy to do work or form heat. 

 Also the formation of body fat may be looked upon as a storage of energy, 

 because it may be used as a source of energy to do work or for heat at any 

 time when the ration is insufficient for these purposes. Hence, in addition 

 to a knowledge of the digestible nutrients in feeds, the scientific stock- 

 feeder should have a knowledge of the energy values of feeds, i. e., the 

 value of different feeding-stuffs for doing work, storage of fat, milk pro- 

 duction, etc. Energy values of feeding-stuffs are expressed in "therms." 

 A therm is the amount of energy in the form of heat necessary to raise the 

 temperature of 1000 pounds of water 4 F. The energy values of some of 

 the common feeding-stuffs are given in Part IV, Table II. 



Feeding-stuffs. In general, feeding-stuffs may be divided into two 

 classes, concentrates and roughages, according to the amounts of digestible 

 nutrients and their energy values. 



