326 SCIENTIFIC FEEDING OF ANIMALS 



protein upon the percentage amounts of protein 

 or fat in the milk has been observed. It is only 

 when the body is much reduced in protein that 

 the milk becomes poorer in fat and more watery. 

 The amount of digestible protein which is essential 

 for the production of a given quantity of milk 

 depends to a certain degree upon the non-nitrogen- 

 ous nutrients in the food. Just as fat and the 

 carbohydrates can diminish protein metabolism in 

 the formation of flesh (p. 72), so can they also act 

 in the production of milk. It is possible, in fact, 

 by a plentiful use of carbohydrates, to so reduce the 

 metabolism of the food-protein in cows that no 

 more is decomposed than the animals require 

 for the maintenance of life. This saving can go 

 so far that all the digestible protein substance 

 above that needed for maintenance (0-5 Ib. per 

 1000 Ibs. live weight, p. 245) can be utilised for the 

 formation of milk without any call being made upon 

 the protein of the body. Such a result is possible, 

 not only when moderate yields of milk are got, but 

 when the amount is as high as 32 Ibs. per head per 

 day. 



This fact, which has been proved from many sides, 

 does not justify the protein content of the milk 

 being taken as a measure of the protein to be given 

 in the food. As far as is known, it does not conduce 

 to a vigorous activity of the mammary gland to 

 supply ^it with only as much protein matter as is 



