THE AMERICAN NAT ill . 1 Lis I 



[Vo 



shown here. The one and one and one half year class 

 and the classes over ten years of age were small. For 

 this reason unbalanced and irregular results would be 

 expected for these classes, and by referring to the curves 

 it will be seen that the premise was justified. The two 

 and three year classes were represented by 1,690 and 

 1,346 individuals, respectively. 



Table III gives the average deviations, mean pounds of 

 milk, standard deviations, correlation coefficients and re- 

 gression coefficients of the population with respect to age 

 and pounds of milk and pounds of fat. Although the 

 •mean age is four years, the three and one half year class 

 actually reached the mean pounds of milk of the popula- 

 tion, as can be seen from Table IV. Correlation probably 

 amounting to causation is shown in the tables up to six 

 years of age, and after that age is reached the correla- 

 tion is practically zero. 



Standard deviation 



Mean pounds 



Mean age 



Correlation coefficient , 



Eegression weight to age . 

 Eegression age to weight ... 

 Coefficient of variability C , 



4 ± 0.449 



5 ± 0.635 

 ± 0.013 



1.11 ± 

 0.29 

 26.0 ±0 



Table IV. This table gives the means, average devia- 

 tions, and plus deviations of the different age classes for 

 both milk and fat production. From these tables the 

 curves for milk and fat production were plotted. They 

 formed also the basis for calculating the curve which is 

 used as a comparison with the Holstein-Friesian curve of 

 fat and milk requirement. These tables also afford an 

 interesting study from the standpoint of capacity of 

 cows for milk production at different ages. 



Considering first the curves for milk production (Fig. 

 1) it will be noted that curve 1, which represents the 



