322 SCIENTIFIC FEEDING OF ANIMALS 



period of lactation, have the greatest effect upon the 

 milk yield. The food, along with other factors, plays 

 a less important part, and only exerts an influence 

 within the limits of the capacity of the mammary 

 gland. It is upon the food, though, that the efficiency 

 of the gland very largely depends. 



In the above sentences a large number of the 

 relations between food and milk production find 

 an explanation. The mammary gland is most 

 active shortly after the birth of the calf, and it is 

 here that the greatest latitude is left for the action 

 of the food. Later, when the gland from natural 

 causes loses more and more of its activity, the most 

 liberal feeding cannot maintain the milk yield at 

 its former high level. Too much food in the second 

 half of the lactation period, therefore, causes the 

 deposition of fat, and when the mammary gland is 

 fat its capacity is reduced. 



From the part played by the mammary gland 

 in the process of milk secretion, it is easily explained 

 why the food, as will be seen later, has such a 

 slight influence upon the composition of the milk. 

 The animal organs one and all have a very constant 

 composition; the lime of the bones cannot be re- 

 placed by the other similar alkaline earths (barium 

 or strontium oxides and magnesia), nor the potash 

 in the organism by the very analogous soda. Fur- 

 ther, the protein substances in the blood cannot be 

 replaced by others of a similar kind, nor can the 



