i yo THE CHEMISTRY OF CATTLE FEEDING 



discussed. For present purposes the average may be taken 

 to be as follows : 



Per cent. 



Water 87-5 



Nitrogenous matter . . . 3-5 



Fat . .' . 3-8 



Milk sugar 4*5 



Ash 07 



lOO'O 



Apart from water and ash, which may be ignored for the 

 present, 100 Ibs. (10 gallons) of cow's milk contains, on the 

 average, 3*5 Ibs. of protein, 3*8 Ibs. of fat, and 4*5 Ibs. of 

 milk sugar, all of which are derived, directly or indirectly, 

 from the food. 



The quantity, i.e. the daily yield per head, varies within 

 wide limits. Cows never produce 100 Ibs. of milk per day. 1 

 Prize-winners at shows rarely give more than about half that 

 amount, and the average for ordinary good milkers is probably 

 not much over a quarter about 2\ to 3 gallons per day. The 

 yield is always greatest soon after calving, and declines 

 steadily till the end of the period of lactation. 



That portion of the food which is given in addition to the 

 maintenance ration to provide for milk production must be 

 of a readily digestible character. The constituents of any 

 portion of the food that is spent on the work of digestion are 

 lost to the milk ; and if the process of digestion occupies 

 a long time, the formation of milk must be slow and the yield 

 consequently small. 



Protein. The protein of the milk must necessarily be de- 

 rived mainly from the protein of the food. It cannot be formed 

 from the non-nitrogenous nutrients (fat and carbohydrates); 

 but various experiments tend to show that a certain amount of 



1 The records of the University of Wisconsin (Bui. 106) contain 

 an account of a cow, "Johanna," which gave over 100 Ibs. of milk per day 

 for several days in succession. In numerous instances cows have given 

 between 80 and 90 Ibs. of milk per day. These cases are, however, 

 exceptional. 



