AGE OF COW IN RELATION TO MILK YIELD 



1 



the relation of these raw average milk yields at one age to those; of 

 a constant age, say 8 years. However, it is better to determine the 

 curve for the data thus eliminating the irregularities due to lack of 

 numbers. Such a curve may be fitted to these data by the method 

 of least squares. When thus fitted the curve is found to be: 



Mean milk yield = 6372.6 + 827.9a - 51.8a 2 + 1394.6 log (a - 1.25) 



where the age (a) is in years and the origin is zero years. 



The student may calculate the points in this curve for each six 

 months of age beginning with 1 year 9 months and plot them on 

 his plot of the raw average milk yield. The completed figure on 

 page 85 when plotted from data of page 86 will be like that shown 

 below. 



3:9 



5.<> 79 99 11-9 13V 



A(jE 



From these data the correction factors of milk yield for age may 

 be determined. These factors are taken as the ratio of the milk 

 yield at 8 years divided by the milk yield at the age from which 

 correction is made. Thus the correction factor for the milk yields 

 of cows at 2 years to the eight year standard would be 



10837 2 

 7647.0 



or 1.41; 



* This method of determining the correct ton factors lor age and milk yield 

 is the one customarily employed with results which arc satisfactory for prac- 

 tical purposes. A slightly more exact method takes into account not only 

 the changes in the mean milk yields with age bul also the changes in the 



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