42 PRINCIPLES OF FEEDING FARM ANIMALS 



expended in the digestion and assimilation of one pound of 

 the hay, and must be deducted from the available energy to arrive 

 at the net energy of the feed, which measures its actual value for 

 productive purposes. 



Experiments with different kinds of feeding stuffis have shown 

 that the energy expenditure caused by the consumption of 100 

 pounds of dry matter is, on the average, no greater for roughage 

 than for concentrates; in fact, it is on the contrary somewhat 

 lower. The average increase in heat production for twelve different 

 coarse feeds came to 46.5 therms per 100 pounds dry matter (rang- 

 ing from 35 to 57 therm's), against 52.8 therms (ranges 1 44 to 62) 

 for ten different concentrated feeds; or expressed percentagely, 24 

 and 27 per cent, respectively, for coarse and concentrated feeds. 

 The lower feeding value (net energy) of coarse feeds is therefore not 

 due to the greater additional work imposed by the mastication and 

 digestion of these feeds, and the mechanical work required in the 

 digestion is, therefore, in the case of ruminants (cattle) at least, 

 only a small part of its total energy cost. German investigations, 

 on the other hand, made with horses and sheep, have shown the loss 

 of energy due to the mastication of feed alone to be considerable ; 

 in the case of hay, e.g., over 50 per cent of the energy value of the 

 digestible matter, and only 10 per cent of that from corn was lost 

 in masticating the feed (see p. 280). 



Net Energy. It has been shown that the loss of energy due to 

 feed consumption, as well as that passed off in the excreta, must be 

 deducted from the total energy of the feed in order to obtain its net 

 energy value. It has not been feasible to make direct determinations 

 of the energy balance for all available feeding stuffs, owing to the 

 large amount of labor and expense involved in making respiration 

 trials, but in the case of feeds 1 for which no direct trials have been 

 made, the net energy values may be computed on the basis of the re- 

 sults obtained with representative feeds of the same kinds. The 

 following example of the method of computation for average tim- 

 othy hay and wheat bran is taken from records of experiments con- 

 ducted at the Pennsylvania station. 4 



Timothy Hay Wheat Bran 



Total dry matter 88.4 Ibs. 88.5 Ibs. 



Digestible protein 3.0 Ibs. 12.0 Ibs. 



Carbohydrates 42.8 Ibs. 41.2 Ibs. 



Fat 1.2 Ibs. 2.9 Ibs. 



Total digestible organic matter. . 47.0 Ibs. 56.1 Ibs. 



Available energy, therms 47.0 X 1.59 = 74.73 56.1 X 1.77 99.31 



Loss in heat production, 88.4 X .3574 = 31.36 88.5 X .5339 = 47.25 



Net energy value, therms 43.37 52.06 



4 Penn. Bui. 142; Armsby, "Nutrition of Farm Animals," p. 675. 



