FORBES! MINERAL ELEMENTS IN NUTRITION 445 



largely to the silicon of timothy hay, caused an acid reaction 

 and an increase in the ammonia of the urine. 



From this study it appears that a failure to maintain mineral 

 equilibrium must be so common among cows of the more profit- 

 able sort that it may be considered a normal condition during 

 the time of larger production, at least if this occurs during the 

 winter, that is, while the cows are off from pasture. 



A common failure of cows to maintain exceptionally high 

 production during consecutive periods of lactation may be due 

 to mineral depletion, as may also be a frequent failure of cows 

 to breed after having been subjected to a period of forced pro- 

 duction, as in the establishment of records. 



Since extensive milk production is sustained, in part, by drafts 

 upon the mineral reserves of the body; since this process can 

 not continue indefinitely; and since there is in cows a gradual 

 shrinkage and final cessation of milk production coincident 

 with this depletion of nutrient reserves, it is believable that this 

 mineral exhaustion may be among those factors which cause the 

 gradual shrinkage of milly, and that by preventing, as largely 

 as possible, these losses from the body we may be able to lessen 

 the shrinkage and to extend the duration of the production of 

 milk. 



The results of this study indicate that especial attention should 

 be given to the calcium, magnesium and phosphorus contents 

 of the rations of heavily-producing cows, in order that the loss 

 of these elements from the skeleton may be kept as low as pos- 

 sible; and a liberal supply of foods rich in these elements should 

 be allowed after a cow has ceased to produce heavily, during 

 the latter part of the period of lactation, in order to refund pre- 

 vious overdrafts before the birth of the next calf. 



It is impossible, of course, to draw any one conclusion which 

 will express the full significance of so varied a program as that 

 which I have reviewed with you, but to me the results of these 

 studies have appealed, more than in any other way, as related 

 to the service of lime and legumes in agriculture. 



Calcium is very much the most abundant mineral in the ani- 

 mal body. Physiologically it is the great mineral stabilizer. 



