188 Maine Agricultural Experiment Station. 1920. 



present study includes besides these records those of volumes 

 28 and 29. One noticeable fact which appears in the study of 

 these later records, is the advance in the mean age of the cows 

 which are tested for 365 day records over. that of the previous 

 study. 



These records are arranged alphabetically according to the 

 names of the cows in the advanced registry. Such an arrange- 

 ment gives no clue as to any relationship which may exist be- 

 tween the attributes age and yearly milk yield and age and yearly 

 butter-fat percentage. The data have been rearranged in a cor- 

 relation table to allow the determination of these relations. 



Two thousand five hundred and eighty-six complete 365 

 day records of the milk yield and age, and butter-fat percentage 

 and age were available for study. 



These records range from an age of 1 year and 6 months — ■ 



2 years to 15 years — 15 years and 6 months. The milk produc- 

 tions range from 6000-7000 to 31000-32000 pounds for the year 

 period. The butter-fat percentage ranges from 2.4-2.5 to 4.6- 

 4.7 per cent. The size of the range obviously requires a group- 

 ing of the material into classes. These classes have been chosen 

 as 6 months for age commencing at one year and 6 months. 

 The class interval for milk yield was taken as 1000 pounds of 

 milk commencing at 6000 pounds for the year. The class inter- 

 val for the butter- fat percentage was chosen as 0.1 per cent. 



The resulting correlation tables are shown in tables 1 and 3. 

 Table 1 shows the association of milk yield with age and table 



3 the association of butter-fat percentage with age. 



The mean milk yield for this group of cows was 16233.6 

 pounds for the year period. The standard deviation or the 

 amount which they varied was 4039.3 pounds and the coefficient 

 of variation of the milk yield was 24.9. The mean age at which 

 these cows were tested was 4.57 years. The standard deviation 

 for the ages was 2.25 years and the coefficient of variation was 

 49.11. It will be noted that the milk yield is slightly higher than 

 that published for the first group of these data 10 as taken from 

 volumes 18-28 of the previous paper. The slight increase in 

 milk yield no doubt comes from the slight increase in age of the 

 cows tested in the later volumes. 



"Loc. cit. 



