Wilson — The Variations of Milk Yield with the Cow's Age. 99 



or not at the time of the last test in (the recording year), had not been succeeded 

 by the birth of a calf in that year." 



Dr. Tocher, who kept the figures for the two years 1911 and 1912 separate and 

 made estimates or scales for each of these years,' made use of both " complete " 

 and " incomplete " lactation yields, and thus used data nearly parallel with those 

 iised by Dr. Pearl and Mr. Miner ; but his scales are expressed in gallons per 

 lactation instead of gallons per week. If these three scales are miiltiplied by the 

 numbers which bring the figures at eight years old to 100, they can be compared, 

 not only with each other, but with the two earlier scales. None of these three 

 scales reached maximum at eight years old, but this does not spoil the comparison. 

 Besides, it is doubtful, as we shall see later, if any of the scales indicates clearly the 

 year at which the maximum is reached. 



These columns, in which the five scales are reduced to a comparable basis, 

 suggest that, since they are inconsistent with each other, the three Ayrshire scales 

 may not indicate correctly the variation of milk-yield with age. It will be noticed 

 that all five scales are closely agreed as to five-, six-, seven-, and eight-year-old cows, 

 but the two earlier scales disagree with the Ayrshire ones about younger cows. 

 In view of the excellence of Mr. Gavin's method and of the probability that his 

 figure for three-year-olds would have approached that for the Dairy Show cows had 

 his cows been classified by age, it does not seem likely that scales can be accurate 

 which make four-year-old Ayrshires proportionately higher yielders than four- 

 year-olds of other breeds, three-year-old Ayrshires equal to other four-year-olds; 

 and two-year-old Ayrshires much better than other three-year-olds. Still less is 



' " Transactions" of the Highland and Agricultural Society of Scotland for 1919, p. 246. 



s2 



