2. Digestibility of Cattle Feeds. 



The several groups of nutrients above described, which make up the 

 various cattle feeds, are valuable to the animal only in so far as they I 

 can be digested and assimilated. The concentrated feeds are consid- 

 erably more digestible than the coarse fodders, as a single illustration 

 will show. 



In the first and fourth columns are given the composition of average 

 samples of timothy hay and of gluten feed. In the second and fifth 

 columns are shown the percentages of the different groups which are 

 digestible. Thus, of the 6.3 pounds of the protein in timothy, 48 per 

 cent are digestible, or 3 pounds; and of the 26.2 pounds of protein in 

 100 pounds of gluten feed, 85 per cent or 22.3 pounds, are digestible. 

 Excluding the ash, which is not generally taken into account, it is 

 shown that 100 pounds of timothy hay contain about 48 pounds of 

 digestible or actual food material, and 100 pounds of gluten feed 78 

 pounds. It is evident, therefore, that the gluten feed is decidedly more 

 valuable as a source of nutrition than the timothy hay. 



3. Method of Measuring the Efficiency of Feeding Stuffs. 



The digestibility of a feed, however, is not the true measurement of 

 its nutiitive value, for the reason that some feeds require more energy 

 for their digestion than others. What is termed net energy value, ex- 

 pressed in the form of calories' or therms,' represents more accurately 

 the true nutritive values of feeding stuffs. 



Explanation. The entire amount of heat or energy contained in a 

 feeding stuff is termed its total heat or energy value. All of this heat or 



' A calorie represents the amount of heat necessary to raise i gram of water i" Centigrade. It 

 is the unit of heat measurement. A therm represents the amount of heat required to raise looo 

 kilograms of water i" Centigrade. 



