Systematic Control of Genital Infections in Herds 703 



include copulations with a number of hopelessly sterile 

 cows, as well as a number of copulations by a sterile bull. 

 I think these data fairly representative of the more fertile 

 purebred herds. I know the results are far better than in 

 some herds. The timely elimination of the hopelessly sterile 

 cows and the elimination of the sterile bull would have 

 raised the efficiency notably. A far greater advance would 

 have been made by taking curably infected cows out of 

 breeding for a few weeks and giving them proper surgical 

 attention. As the data stand, they furnish some helpful 

 suggestions regarding the number of cows which may ordi- 

 narily be assigned to a bull. 



Breeding is carried on by two separate plans — massed or 

 seasonal breeding when it is desired to have all calves born 

 during a limited season, and perpetual breeding throughout, 

 or during nine or ten months of the year. A bull may evi- 

 dently make with safety a greater number of copulations 

 during the year if evenly distributed throughout, and can 

 safely make a greater number of copulations in a short in- 

 terval (one week or one month) when he is to be sexually 

 idle the remainder of the year. Such observations as I have 

 been able to make have led me to regard an average of two 

 copulations per week throughout the year as the probable 

 maximum of efficiency, measured by the percentage of preg- 

 nancies, their safety, and the vigor of the young. Taking 

 the above data as a general average of fertility, a healthy 

 adult bull would suffice for about forty cows (100 copula- 

 tions) . 



When the breeding is massed, the frequency of coitus 

 should still be held under reasonable control. Probably the 

 frequency of coitus may be advanced to four or five times a 

 week for a period of four to six weeks. Bulls have done 

 more than this, but my studies indicate that usually they 

 undergo a gradual decline in fertility year by year and go 

 down so far that they do not eventually regain their initial 

 sex vigor. When mass breeding is undertaken in pasture, 

 the ratio of females must be very low, especially if all are 

 ready to be bred when the bull is placed with them. Under 



