4 MAINE AGRICULTURAL EXPERIMENT STATION. 



various times. The average production of the herd per cow in 

 the last year was 7500 lbs. of milk. Herd Y is also made up 

 of cows of various ages, but most of them are young, i. e., under 

 full maturity. They freshened at various times and gave for, 

 the year an average flow of 6000 lbs. per cow. Is Herd X a 

 better producing herd than Herd Y, taking age of cOMrs, average 

 stage of lactation, etc., into account? 



Hitherto there has been no definite scientific method of 

 dealing with this problem. The need for something of the sort 

 was first urged to the writer by Mr. H. M. Look, the tester for 

 the Winthrop Cow Test Association. It was suggested that 

 the problem might be looked at in the following way. On the 

 average a cow may be regarded as working at her maximum 

 efficiency when she is, on the one hand, fully mature in age, 

 but not too old, and on the other 'hand, at the beginning of a 

 lactation period, say during the first month. Suppose this 

 maximum efficiency be designated as 100 per cent. Then the 

 cow's efficiency in performance at any other age or stage of 

 lactation will be represented by some percentage below 100. 

 Given the proper data, and by the use of appropriate mathe- 

 matical methods, it is possible to construct a table which will 

 give these efficiency percentages at various ages and months 

 of lactation. Such a table has been prepared in this laboratory 

 and is herewith presented as Table 2. The method of calculat- 

 ing this table cannot be gone into here for lack of space, but. 

 will be presented in a later publication. 



The manner in which the table is to be used may be shown 

 by an example. Let us compare two herds of Holstein cattle, 

 of approximately the same size and on nearly the same date. 



