ILLINOIS STATE DAIRYMEN'S ASSOCIATION. 211 



VARIATION IN THE* DAILY MILK AND BUTTER PRODUCTION OF 



COWS. 



The quantity of milk produced by a cow and the 

 quality of the milk are influenced directly by the indi- 

 viduality, and indirectly by the breed of the animal. 

 Each breed is only a group of individuals of the same 

 kind. The breeds differ from each other by certain 

 characteristics which are preserved so long as condi- 

 tions are not sufficiently strong to change them. To 

 the distinct characteristics belongs the disposition to 

 produce a large quantity of milk, or milk possessing a 

 specific peculiarity, such as high content of butter fat 

 and casein. 



Numerous observations show that with nearly all 

 cows the milk production follows the general course of 

 decreasing in quantity of milk and b # utter, and increas- 

 ing in percentage of butter fat as the period of lacta- 

 tion progresses. 



By weighing and testing the milk of cows every day, 

 I have observed that lines representing the daily pro- 

 duction of milk and of butter fat do not take the course 

 of a straight line down an inclined plane, but are 

 broken, zigzag lines. Some of the results of these 

 observations have been represented graphically in a 

 bulletin of the station. 



The broken lines of the diagram show the production 

 of the cows from day to day, and are evidence to illus- 

 trate, First: That the variation from day to day in the 

 morning's and evening's milk considered separately 

 was greater than in the mixed milk for the day. 



Compare plate 1 with plate 2. 



Second: That under exactly the same conditions, 



