80 



MANUAL OF DAIRY CATTLE BREEDING 



pounds of milk as seen from the method in which the table is grouped. 

 The value of X is assumed to equal the mid-point of that particular 

 group so that X = 1 is really equal to 4500 pounds of milk. The 

 zero origin is consequently equal to 4500 — (1 ; the value of X, 

 multiplied by 1000, the class interval) or 3500. Then the mean of 

 the first group is equal to 



3500 + 3.762295 X 1000 = 7262.3 pounds of milk 



In like manner the other average milk yields for the different 

 ages may be obtained. These are shown in the following table. 



AGE AT TEST 



year 6 months to 1 year 11 months 

 years months to 2 years 5 months 

 years 6 months to 2 years 11 months 

 years months to 3 years 5 months 

 years 6 months to 3 years 11 months 

 years months to 4 years 5 months 

 years 6 months to 4 years 11 months 

 years months to 5 years 5 months 

 years 6 months to 5 years 11 months 

 years months to 6 years 5 months 

 years 6 months to 6 years 11 months 

 years months to 7 years 5 months 

 years 6 months to 7 years 11 months 

 years months to 8 years 5 months 

 years 6 months to 8 years 11 months, 

 years months to 9 years 5 months, 

 years 6 months to 9 years 11 months 

 years months to 10 years 5 months, 

 years 6 months to 10 years 11 months, 

 years months to 11 years 5 months, 

 years 6 months to 11 years 11 months, 

 years months to 12 years 5 months, 

 years 6 months to 12 years 11 months, 

 years months to 13 years 5 months, 

 years 6 months and above 



MEAN- 

 MILK YIELD 



,262 

 ,042 

 ,453 

 ,710 

 ,284 

 ,637 

 ,975 

 ,390 

 ,321 

 ,598 

 ,450 

 ,812 

 ,709 

 ,887 

 ,910 

 ,829 

 ,766 

 ,739 

 ,636 

 ,471 

 ,923 

 ,677 

 ,250 

 ,571 

 441 



(The different members of the class may check the results for 

 the different rows.) The student by plotting these means shows 

 that there is a relation between milk yield and age of the cow. To 

 place the milk yields of cows on comparable age basis we might use 



