332 NUTRITION OF FARM ANIMALS 



nary way, of approximately i : 12. On such a ration there 

 would, in all probability, be some loss of digestibility and an in- 

 crease of its protein by 50 per cent might perhaps effect a gain in 

 digestibility which would more than offset the increased cost, 

 if any. Indeed, unless feeding stuffs especially poor in protein 

 are used, it may often be difficult, even were it desirable, to 

 reduce the protein content of a maintenance ration to the low 

 level of absolute necessity. 



2. THE ASH REQUIREMENTS FOR MAINTENANCE 



421. Ash ingredients indispensable. That a supply of 

 the so-called mineral or ash ingredients, as well as of protein 

 and of energy yielding materials, is necessary for the growth and 

 maintenance of animals has been fully recognized since the 

 time of Liebig, and was strikingly demonstrated by the well- 

 known experiments of Forster 1 and of Lunin, 2 which showed 

 that animals supplied only with ash-free feed perished even 

 sooner than when deprived of all feed. 



Some of the reasons for these facts were indicated in the dis- 

 cussion of the functions of the nutrients in Chapter V (268-272), 

 where it was shown that, besides their structural importance 

 for both the skeleton and the soft tissues, the presence of ash 

 ingredients in the body fluids is essential to the maintenance 

 and regulation of the vital processes. Aside from the specific 

 uses of single elements, such as iron, fluorin, iodin, etc., three 

 general functions of the ash ingredients as a whole were there 

 mentioned, viz., the maintenance in the body fluids and tissues 

 of the normal osmotic pressure and of the relative concen- 

 tration of the various ions, and, as a specific case of the latter, 

 the preservation of neutrality. 



422. Ash content of feed large. Most feeding stuffs, how- 

 ever, and particularly the mixed rations of farm animals, con- 

 tain what appear at first sight to be much larger amounts of 

 ash ingredients than the body requires. Milk production, for 

 example, causes an exceptionally large drain upon the ash 

 content of the body, yet even rations made up of materials 

 relatively poor in ash contain much larger amounts than are 



1 Ztschr. Biol., 9 (1873), 297. a Ztschr. Physiol. Chem., 5 (1881), 31. 



