690 Diseases of the Genital Organs 



B. abortus is the cause of abortion and that it disappears 

 from the uterus of an aborter very shortly after the disaster. 

 If then a cow aborts and the abort and its membranes are 

 burned or buried, the stall disinfected, and the cow quaran- 

 tined for a brief interval, the infection is controlled and 

 from such standpoint the seller may declare he has no "con- 

 tagious abortion" on his premises — ^but he may have an hour 

 or two later. The buyer should not exercise himself seriously 

 concerning "contagious abortion," but should try to deter- 

 mine whether the animals he wishes to purchase are capable 

 of begetting or of giving birth to healthy calves. 



4. Intelligent breeders aim to retain their best cattle and 

 to discard the least valuable. It is only when a breeder ex- 

 ceeds his holding capacity for good animals that he becomes 

 desirous of selling some of them. It is commonly assumed 

 that the breeder of purebred cattle has a far greater ca- 

 pacity for profitably holding females than males. The dif- 

 ference has been vastly overdrawn, owing to reproductive 

 inefficiency. Thoroughly healthy cows breed regularly up to 

 twenty years and often beyond. Ideally each cow should 

 produce one healthy calf each twelve months. If she gives 

 birth to her first calf at two years and breeds ideally up to 

 and including her thirteenth year, she will have produced 

 twelve calves, six of which, upon the average, will have been 

 males and six females. At the close of the thirteenth year, 

 it will be necessary to have in reserve one adult from her 

 six female calves to replace the worn-out original cow, and 

 there will remain for disposal (or for herd expansion) six 

 males and five females. 



When the average breeding life of the females in a herd 

 falls below six years and the average number of progeny 

 falls below four, the preponderance of males over females 

 offered for sale by the breeder becomes very marked. He 

 must in the latter case retain fifty per cent, of his female 

 progeny to replace the toll exacted by disease, whereas, 

 with the ideal cow of thirteen years with twelve calves, he 

 retains but 16 2/3 per cent, of his female progeny to main- 

 tain his herd status. The breeder having a herd of low effi- 



