MAINTENANCE THE ENERGY REQUIREMENTS 283 



But the difference between the metabolizable energy and 

 the work of digestion is the net energy (370). Consequently 

 the foregoing statement is equivalent to saying that the main- 

 tenance requirement of the steer was 5392 Cals. of net energy. 

 Each pound of this particular hay had a net energy value of 

 502 Cals. To maintain the animal, therefore, there would be 

 required 5392 -s- 502 = 10.74 lb., as previously computed. 



375. Manner of stating the maintenance requirement. 

 Evidently the maintenance requirement of an animal, such as 

 the steer of the foregoing illustration, may be stated in a va- 

 riety of ways in terms of weight of feed, of amounts of di- 

 gestible nutrients, of metabolizable energy or of net energy. 

 So far as the results of a single experiment are concerned, it 

 makes little difference which manner of statement is adopted, 

 since they are all simply different ways of expressing the same 

 facts. When it is desired to make general statements, however, 

 there are very manifest advantages in stating the maintenance 

 ration in terms of net energy. 



It was shown in Chapter VII (343) that the fasting katabo- 

 lism might be regarded as practically constant under uniform 

 conditions. Consequently the net energy requirement for 

 maintenance is equally constant, and in the foregoing example 

 any ration having a net energy value of 5392 Cals. would 

 have been a maintenance ration. 



But since the net energy values of different feeding stuffs, 

 as well as the proportion of their metabolizable energy which 

 can be utilized for maintenance, may vary through a consider- 

 able range, the weight of feed or the amount of metabolizable 

 energy which will suffice to maintain an animal will vary with 

 the kind of material fed. For example, it is shown in subsequent 

 paragraphs (380, 381) that a thousand-pound steer requires 

 about 6.0 Therms of net energy for maintenance. From the 

 results of Armsby and Fries' determinations of net energy values 

 (760), it is easy to compute that to supply this amount in tim- 

 othy hay with a net energy value of 48.63 Therms per 100 

 pounds of dry matter would require 6.0 -4- 0.4863 = 12.34 

 pounds of dry matter, but that if mixed hay with a net energy 

 value of 43.37 Therms per 1000 pounds were used, the amount of 

 dry mattes necessary would be 6.0 -f- 0.4337 = J 3-83 pounds. 

 The quantities of metabolizable energy contained in these main- 



