2l8 AGRICUI.TURE OF MAINE. 



per cent above the general average of the breed for mature 

 cows is sufficiently high to get the best results in the direction 

 of breed improvement, 



(b) A DAIRY EFFICIENCY TABLE. 



The following kind of question constantly arises in cow- 

 test association work: Herd X is made up of cows of various 

 ages, from 2 to 14 years, the majority of the cows being fully 

 matured (six years or over). These cows last freshened at 

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

 the last year was 7,500 pounds 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 6,000 pounds per cow. Is Herd X a 

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

 stage of lactation, etc., into account? 



Hitherto there has been no definite scientific method of deal- 

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

 was first urged to the writer by 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 aver- 

 age a cow may be regarded as working at her maximum effi- 

 ciency 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 lacta- 

 tion period, say during the first month. Suppose this maximum 

 efficiency be designated as 100 per cent. Then the cow's effi- 

 ciency 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 mathematical meth- 

 ods, 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 here- 

 with presented as Table 2. The method of calculating this table 

 cannot be gone into here for lack of space, but will be presented 

 in a later publication. 



