106 THE STOCKFEEDER'S COMPANION 



crops (straw) throws a considerable amount of internal 

 work on an animal, since it has to be chewed and mixed 

 with saliva (masticated), carried along the alimentary 

 track and dealt with by the stomach, intestines, etc. 

 The work of the excretory organs is also increased, and 

 it appears that the nutrients in bulky fodders have not 

 much value for the production of increase or energy, but 

 are valuable chiefly for the production of heat in the 

 animal body. Zuntz showed that with a horse fed 

 entirely on wheat straw, which is one of the hardest and 

 most indigestible of straws, that the energy required to 

 deal with this hard, coarse food was greater than the 

 energy supplied by the food ; hence the horse ultimately 

 died. 



We have already seen that the production of work 

 (external energy) and increase in body weight can only 

 be obtained from the margin of nutrients which are 

 left after the nutrients have supplied the animal with 

 the necessary energy to deal with (masticate) the food 

 in the mouth, as well as along the alimentary track till it 

 leaves the system. The bulky part of the ration leaves 

 such a small residue or surplus of digestible nutrients 

 for production, that it is necessary to add concentrates 

 to these bulky foods to raise the whole character of 

 the ration. 



This is brought about in the following way : Con- 

 centrates are, generally speaking, foods which are rich 

 in nutrients of high digestibility. The energy required 

 for mastication, etc., is comparatively small, consequently 

 there is a large surplus of nutrient material for produc- 

 tion, and when added to the bulky food they raise the 

 available surplus for production of each pound of the 

 ration considerably above that of the original bulky 

 food, 



