4i8 



NUTRITION OF FARM ANIMALS 



the digestive tract, and still more upon the effect of other ele- 

 ments on the elimination of phosphorus. An amount of this 

 element amply sufficient to meet the normal demand when 

 supplied in one ration might be quite inadequate in another of 

 a different character. 



Since the intestines are the normal path of excretion for 

 some ash elements (164, 199), a computation of the digesti- 

 bility of these elements in the ordinary sense, by comparing 

 the amounts in feeds and feces, gives an entirely false idea of 

 their availability. Moreover, it was shown in Chapter IX 

 (429-433) that the rate at which mineral elements are lost 

 from the body depends to a large degree upon the qualitative 

 composition of the ash of the feed, variations in the supply of 

 one element sometimes affecting materially the gain or loss of 

 another. In particular it was pointed out that the proportion 

 of acid and basic elements and to a less degree the ratio of 

 potassium to sodium may have striking effects of this sort. 

 For example, in Weiser's experiments on pigs (493), the ad- 

 dition of 5 grams of calcium carbonate to a ration of 1000 

 grams of maize not only changed a loss of calcium into a gain 

 but also produced the same effect on the phosphorus balance, 

 so that a phosphorus supply which was previously insufficient 

 to maintain the body was able to support a material gain. 



TABLE 106. ASH BALANCE OF SWINE WITH AND WITHOUT CALCIUM 

 CARBONATE 



