98 Scientific Proceedings, Royal Dublin Society. 



successive lactations, were brought together by Mr. Gavin and the average 

 revised maximum yields iu quarts a day' : — ■ 



Sixth Seventh Eighth 

 221 148 83 



15-85 15-51 15-48 



Had Mr. Gavin been able to classify his cows by age rather than lactations, 

 his scale would probably have stood for good, for cows' yields vary with the years 

 they have lived rather than with the lactations they have passed. As it stands, 

 however, it needs to be only slightly revised by the figure for three-year-olds 

 being raised iu proportion as it was lowered originally through some of his 

 " first lactation " cows being only two-y-ear-olds. 



By reducing them to a common base we shall see how far the two scales agree ; 

 and, since both are at their highest when the cows are eight years old, 

 they can be reduced by multiplying the figures in each scale by the number 

 which brings their highest figure to 100. Assuming Mr. Gavin's first lactation 

 cows to have been three-year-olds and the rest to have been a year older with 

 each succeeding lactation, the result is : — 



Age, .... 3 4 



Dairy Sliow cows' \ 



yields multiplied ( --.q qi 



[ 100 67 8 81 



Essex cows' yields ) 

 multipliedby^-^:^-^,) 



When allowance had been made for the pi'obability that some of the Essex 

 first lactation cows were two-year-olds, these two scales agreed so closely that 

 it was assumed they indicated very fairly how the cow's yield varies with her age. 

 But confidence in them was sliaken by papers published in the " Journal of 

 Agricultural Eesearch" for September, 1919, by Dr. Kaymond Pearl and Mr. Miner, 

 and iu the "Transactions" of tlie Highland and Agricultural Society of Scotland 

 for the same year by Dr. J. F. Tocher. These workers made use of the Ayrshire 

 cow records published by the Scottish Milk Eecords Committee. Systematic 

 milk-testing was begun among breeders of Ayrshire cattle in 1903 by the 

 late John Speir, who, for the first five years, published annual reports in the 

 " Transactions " of the Highland Society, while subsequent reports have been 

 published separately by the Milk Eecords Committee. In these reports the cows 

 were not always classified upon the same plan. Till that for 1910, the dates 

 the cows were due to calve again wei'e not given, nor were the yields of in-calf covrs 

 separated from those which were not in calf again. Consequently, Dr. Pearl and 

 Mr. Miner's results are based upon the average weekly yields of in-calf and not- 

 in-calf cows during the time they were actually in milk. In the reports for 

 1910, 1911, and 1912 the yields are divided into two classes, according as the 

 cows had " complete " or " incomplete " lactations, which are " a lactation 

 which has concluded in (the recording year) and has been succeeded by the 

 birth of a calf in that year," and another " which, whether the cow was milking 



J "Journal of Agricultural Science" for October, 1913, pp. 378 and 379, 



