704 Diseases of the Genital Organs 



such conditions the bull may copulate several times with a 

 cow during one estrum. If twenty-one cows are assigned 

 to a bull and each has an estrual cycle of twenty-one days, 

 there will be an average of one cow in estrum daily, with 

 the inevitable result that on some days several cows will be 

 in estrum. The number of cows under these conditions 

 should therefore be below twenty, preferably not over fif- 

 teen. If the breeding period extends over ninety or more 

 days, more cows may naturally be assigned to one bull. The 

 breeding of ordinary grade beef cattle in pasture produces 

 the maximum ratio of vigorous calves, if the bulls are 

 healthy and abundant, but, when a perilously infected bull 

 is used, the disaster is inevitably as great, and may be 

 greater than by individual, controlled breeding. The ordi- 

 nary grade beef cow running free at pasture commonly en- 

 joys the maximum of general and sexual health, but it is 

 far from sufficient to withstand the shock from a virulently 

 infected bull. When the bull consorts constantly with the 

 cows, he immediately recognizes estrum, and coitus occurs 

 promptly; in controlled breeding estrum is frequently too 

 far advanced when discovered for coitus to succeed. Many 

 estrual periods are completely overlooked. If observations 

 are made but once daily, a cow may readily come in estrum 

 shortly afterward and the estrum disappear before the 

 next search is made. Indeed the healthiest cows have the 

 shortest duration of estrum, frequently dropping to, or be- 

 low, fifteen hours. This makes it essential to the highest 

 success to make observations for estrum at intervals of about 

 twelve hours. The natural inclination of some breeders to 

 suspend breeding operations on Sunday reduces the effi- 

 ciency 14 per cent. If the estrual cycle in the individual is 

 other than twenty-one days, her estrum may be recognized 

 at its next appearance. But the cycle in the healthiest cows 

 is most frequently twenty-one days, and, once in estrum on 

 Sunday, always in estrum on Sunday, unless the estrual 

 cycle is broken by pressing the corpus luteum from the 

 ovary. 



The maximum degree of safety in sex hygiene is attained 



