MAINTENANCE REQUIREMENTS OF MATTER 333 



found in the milk produced. Zuntz l gives the following com- 

 parison of the ash ingredients in a ration recommended by 

 Kellner for a cow producing 22 pounds of milk daily with the 

 ash content of the milk yield : - 



TABLE 62. COMPARISON OF ASH CONTENT OF RATION AND OF MILK 



Comparisons like the foregoing have tended to confirm the 

 somewhat prevalent idea that rations adequate in other re- 

 spects may be assumed to contain a sufficiency of ash ingredients. 

 This is doubtless true of animals living in a state of nature but 

 it is a questionable assumption under the artificial conditions 

 to which many farm animals are subjected, as when receiving 

 an excess of some single grain like Indian corn or of technical 

 by-products, or when stimulated to a high degree of produc- 

 tion. 



423. Ash ingredients digestible. It is true that of this rela- 

 tively large supply of mineral matter in ordinary rations, a very 

 considerable fraction, especially of certain elements, is found 

 in the feces, and this fact has led to their being regarded as 

 relatively indigestible. As was stated in Chapters III and 

 IV (164, 199), however, this apparently low digestibility arises 

 from the fact that the intestinal tract constitutes the normal 

 path of excretion for certain elements, notably, in the case of 

 herbivora, for calcium and phosphorus. Thus Forster has 

 shown that in the dog the calcium of the feed is largely resorbed 



1 Jahrb. Deut. Landw. Gesell., 1912, p 570. 



