92 Maine Agricultural Experiment Station. 1919. 



from the first two volumes of the Registry of Merit. The mean 

 yearly milk production of each six months age group was de- 

 termined from these data commencing with the age at test of 

 one year and three months. These mean milk productions are 

 shown in figure 23 as small circles. It will be noted that these 

 observational means are only shown up to the age of twelve 

 years and three months. The data actually had means for the 

 milk productions of each of the six months period up to sixteen 

 years and three months. The mean milk production for these 

 last groups depended on so small a number of individual records 

 that they were very irregular. It was consequently thought 

 best to omit these in the calculations. The irregularity shown 

 for the means of eight years and three months to. twelve years 

 and three months is likewise due to lack of numbers in the ob- 

 servations. It has consequently seemed best in the calculations 

 leading up .to the fitting of these observational data with a log- 

 arithmic function to use the first smooth of these observations, 

 as experience has shown that the smoothed observations ap- 

 proach more nearly the direction that the curve would take if 

 based on a larger series of figures. 



The general function which describes the relation of age 

 to amount of milk produced has been shown to be 



y=a-\-bx-\-cx 2 -\-d log x 



When the observational means shown in figure 23 are fitted 

 by such a curve, the theoretical curve shown in the figure 23 is 

 obtained. The equation to this curve is 



y=4586.5o-l-307.55Jir — I2.65^r 2 -|-22i6.62 log x 



A comparison of the observational means and the theoreti- 

 cal means are all that is required to show the close similarity of 

 the two curves. It does not seem necessary therefore to cal- 

 culate the X 2 value for this curve. 



The law which governs the relation of age and milk pro- 

 duction for these Registry of Merit Jersey cows may be ex- 

 pressed in words as follows. In these Jersey cows the absolute 

 amount of milk produced per unit of time increases with the 

 age of the cow until a maximum is reached, but the amount of 

 increase diminishes each year with advancing age until the ab- 



