THE FEEDING OF MILCH CATTLE 327 



secreted in the milk ; a certain excess is necessary 

 in order to counteract the weakening which the 

 gland experiences as the period of lactation ad- 

 vances. If the supply of protein in the food were 

 limited to that which appears in the milk the 

 natural decrease in the milk yield would most 

 certainly be more rapid than if a food richer in 

 protein were fed. It is advisable, then, to reckon 

 for each 10 Ibs. of milk -55 65 Ib. digestible protein 

 in addition to that which the maintenance of the 

 animal demands. 



(d) The effect of non-protein nitrogenous 

 substances. 



Many substances of this nature, such as aspara- 

 gine and ammonia, can, as investigations have 

 shown (p. 66), raise the increase of flesh in rumi- 

 nants. This is very probably due to the influence 

 of bacteria in the partly digested food which con- 

 vert the non-protein substances into proteins, and 

 these are digested in another part of the intestine. 

 In the same way these substances can naturally be 

 utilised for the production of milk. Experiments 

 on this question were first made with asparagine, 

 and afterwards also with the nitrogenous sub- 

 stances extracted from young grass. The results 

 showed that no definite effect upon the formation 

 of milk can be ascribed to the non-protein sub- 



