[ 97 ] 



No. 12. 



THE VAPJATIONS OF MILK YIELD WITH THE COW'S AGE AND 

 THE LENGTH OF THE LACTATION PEEIOD. 



By JAMES WILSON, M.A., B.Sc. 



[Read November 28. Printed Decemker 12, 1922.] 



Ten or twelve years ago it was necessary to have scales by which individual 

 milk yields could be " corrected " for the age of the cow and the length of her 

 lactation. As it was known by that time that a cow's capacity is indicated 

 by her yield when it is at the maximum, a few weeks after calving, a scale 

 was constructed from the average daily yields of the cows .exhibited at the 

 London Dairy Show during the ten or twelve years prior to 1909. Most of 

 these Dairy Show cows are among the best of their kind and, therefore, age for age, 

 of nearly like capacity. They are also shown when their yields are near their 

 best; and it was expected that, if they were classified by age, their average 

 yields, taken class by class, would indicate the variation of yield with age. 

 Unfortunately, the data were not many, and, as there was no separate competition 

 for young cows till a year or two before 1909, very few for tlie younger ages. 

 The number of cows of different ages and their average daily yields were as 

 follows : — 



and over 



A few years later another scale was constructed from better materials by 

 Mr. W. Gavin, who was then making a statistical examination of the records 

 which had been kept in Lord Kayleigh's dairy herds in Essex. He was able 

 to bring together the records of over three hundred cows througli their first five, 

 and gradually declining numbers of the same cows through three more, lactations. 

 Having also seen that a cow's capacity is indicated by her yield at the flush, 

 Mr. Gavin found that the daily fluctuations at this time could be smoothed out 

 and the normal yield determined by reading "the maximum daily yield maintained 

 or exceeded for not less than three entries in the record book." He called this 

 the " Revised Maximum," and thus described how it is determined : " The three 

 highest daily yields (whether entered weekly or daily) are first noted. Four cows, 

 for example, might give 16, 16, 16-16, 16, 17—16, 18, 18—16, 17, 18 quarts. 

 The revised maximum is then fallen as the highest yield common to the 

 three entries. Thus, in all four cases quoted, it would be sixteen quarts. "^ 

 The following table gives the number of cows whose records, through eight 



' " Journal of Agricultural Science " for October, 1913, p. 379. 



SCIENT, PKOC. K.D.S., VOL. XVII., NO. 12. S 



