14 MAINE AGRICULTURAL EXPERIMENT STATION. I917. 



TABLE X. 



Showing the Chief Physical Constants for Variation in Age of Breeding 



Bulls. 



Constant. 



Bulls used as breeders. 



Mean or average age . . 



Median age 



Third quartile age. . . . 

 Standard deviation . . . . 

 Coefficient of variation 



2.921 ± .037 years 



2 . 589 ± . 047 years 



3.844 ± .047 years 



1 . 722 ± . 026 years 



58.94 ± 1.18% 



From these tables we note that the average age of the herd 

 bulls used to sire the 967 calves included in the statistics was 

 just under three years. The median age of these herd bulls 

 was approximately two and a half years. This means that 

 one-half of the calves were sired by bulls under two and a half 

 years old at time of service. Seventy-five per cent of all the 

 calves (as shown by the third quartile age) were sired by herd 

 bulls less than about three years and nine months old at time 

 of service. Less than 15 per cent of the calves were sired by 

 bulls five or more years old. Let us consider for a moment 

 what these facts mean. A bull must be at least four years old 

 before the breeder can possibly have had any opportunity to 

 test adequately the milk producing capacity of his daughters. 

 But 8j per cent of all the calves covered in these statistics 

 were sired by hulls under four years and 10 months of age. 

 In other words, in the breeding operations of a large number of 

 Maine's most progressive and wide-awake breeders (for such 

 the cooperators in this record scheme are) more than three- 

 fourths of the calves produced in a given interval of time are 

 sired by bulls about whose ability to transmit milking qualities 

 absolutly nothing definite can by any possibility be known. It 

 is doubtless entirely fair to assume that essentially the same 

 conditions regarding cattle breeding methods obtain in other 

 places generally. Is it remarkable that progress is so slow? 



For comparison with these figures regarding Maine cattle 

 in general let us examine the facts resrardingf the leading- cows 



