64 



Maine Agricultural Experiment Station. 1919. 



Turning next to the relation of fat percentage to age we 

 have the essential data exhibited in Table 3. 



TABLE 3. 



Mean fat percentage at different ages 



Age in years 



Observed mean fat 



Calculated mean fat 





percentage 



percentage 



2 



3.852 



3.862 



3 



3.903 



3.827 



4 



3.775 



3.793 



5 



3.716 



3.759 



6 



3.685 



3.725 



7 



3.691 



3.690 



8 



3.664 



3.656 



9 



3.636 



3.622 



10 



3.600 



3.607 



11 



3.629 



3.604 



12 



3.599 



3.601 



13 



3.606 



3.598 



14 



3.592 



3.595 



15 



3.500 



3.593 



16 



3.662 



3.590 



From an examination of the observed figures it appears- 

 that in general the fat percentage tends to decline with advanc- 

 ing years of age until the tenth year is reached. From that 

 point on, allowing for chance fluctuations and the fact that 

 the numbers dealt with get progressively smaller, the fat per- 

 centage appears to remain about constant for the rest of the 

 cow's milking life. Consequently, it has seemed best to break 

 the curve at the 10 year point and fit the two parts separately, 

 each with a straight line. The resulting figures are given in. 

 the "calculated" column of Table 3. The equations to the two 

 lines are as follows, the fitting having been done by the method 

 of least squares. 



From 2 to 10 years of age: 



y = 3.896 — .0343^ 

 From 10 to 16 years of age: 

 y = 3.610 — .002&tr 



. 



