BULLETIN 262 



THE CHANGE OF MILK FLOW WITH AGE, AS 



DETERMINED FROM SEVEN DAY RECORDS 



OF JERSEY COWS.i 



By Raymond Pearl and S. W. Patterson. 



From the time of the earhest domestication of cattle it must 

 have been realized that age was a factor influencing milk pro- 

 duction. It is well known among dairymen and breeders that, 

 other conditions being the same, a cow will produce more in a 

 given length of time during her second lactation period than for 

 the same time during her first period. She will produce more 

 her third lactation period than her second; and so on until she 

 reaches mature form, or the age for maximum production. She 

 remains in this mature form for a few years ; then each succeed- 

 ing lactation period decreases in the rate of milk flow. 



Opinions differ somewhat as to the average age at which a 

 cow reaches mature form and as to the rate of increase with 

 which she approaches that form. The general belief is that ma- 

 ture form is reached by the fifth year and that the curve repre- 

 senting the variation in milk flow by lactation periods up to that 

 time is a straight line. 



This latter opinion is evidenced by the requirements for 

 advanced registry in the Ayrshire Breeders' Association rules — 

 the only Association which has a milk requirement for ad- 

 vanced registry entry. Since the variation in the average per- 

 centage of butter fat in the total milk in different lactation peri- 

 ods is slight, the above opinion is substantially concurred in by 

 the entry requirements, which are based on butter fat, in the rules 

 of the other three dairy breeders' associations. The four associ- 

 ations are alike in fixing mature form at five years of age and 

 in allowing nothing for decrease in productivity due to very ad- 

 vanced age. 



^Papers from the Biological Laboratory of the Maine Agr. Exp. Stat. 

 No. 117. 



