MEASURING THE USEFULNESS OF FEEDS 49 



winter in the northern states, than for animals being fed for produc- 

 tion, such as horses at work, growing or fattening animals, or dairy 

 cows in milk. (90, 113, 130, 141, 147) Therefore, rations for idle horses 

 and for wintering beef cattle which are not making much growth or are 

 not being fattened may consist chiefly of such feeds, while animals being 

 fed for large production need more net energy. 



Owing to the great amount of labor involved in making studies of this 

 character with the respiration calorimeter or with the respiration appa- 

 ratus, Armsby and Kellner together determined the actual net energy 

 values for only 21 different feeding stuffs. From the data secured in the 

 studies of these feeds Armsby computed the net energy values for a 

 considerable number of feeds, basing his computations, with the per- 

 mission of the authors of this volume,- upon the average composition 

 of the various feeds given in Appendix Table I and the digestible 

 nutrients given in Appendix Table III. The net energy values thus 

 computed for some representative feeds are given on Page 122. Such 

 net energy values are theoretically more accurate measures of the 

 productive value of different feeds than their content of total digestible 

 nutrients. However, such computed values are but approximations, 

 due to the meager data yet secured. For instance, while practical feed- 

 ing trials have shown corn to have a somewhat higher productive 

 value than barley for fattening animals, the computed net energy value 

 of barley is given as 89.94 therms, which is slightly greater than that 

 of corn. In a few instances, like that just referred to, the computed 

 net energy values are in fact less accurate measures of the actual relative 

 values of feeds than the amount of total digestible nutrients the feeds 

 furnish. 



Furthermore, most of the net energy values which have actually been 

 determined have been found in trials with mature steers. How far these 

 values hold good for other classes of animals is a question. The few 

 trials reported for other animals show surprising differences in some 

 instances. For instance, Kellner found the net energy value of 100 Ibs. 

 of starch to be 81.89 therms in trials with steers, while Fingerling found 

 it to be 151.1 therms in trials with swine. Similarly, the net energy 

 value of peanut oil per 100 Ibs. was found to be 161.71 therms in trials 

 by Kellner with steers, and to be 386.7 therms in trials by Fingerling 

 with swine. For wheat gluten, a similar difference was found, the net 

 energy value being 68.45 therms for steers, and 152.3 therms for swine. 8 

 A comparison of the net energy values for ruminants given in Chapter 

 VII with those for horses, given later (447), will show similar dif- 

 ferences. The computed net energy values must therefore be re- 

 garded not as final, but as helpful estimates which point out important 

 general facts concerning the relative value of different classes of feeds. 



In comparing the net energy values of various feeds it should always 

 be borne in mind that net energy is a measure of the value of a feed for 



8 Armsby, Nutrition of Farm Animals, pp. 660, 662. 



