The Prevention of Contagious Abortion in Cattle. 1> 



udder, and the milk remains infected constantly for periods up to 

 six or seven years in some cases, even after several apparently normal 

 calves have been produced. Uterine infection in a slight degree 

 during gestation remains for several years, the probability being that 

 at every pregnancy after abortion the uterus becomes reinfected from 

 the udder. 



As regards the channels of infection, it seems certain that the 

 great majority of cows become infected bj^ eating infected material, 

 such as portions of an infected afterbirth or food contaminated with 

 the infected discharges from a case of abortion. If a cow does not 

 eat her own afterbirth or portions that break off, it is practically 

 certain to be eaten by other cattle, as one may frequently observe. 



The amount of infection spread during one act of abortion and 

 during the few succeeding days is very great, so that too much care 

 cannot be taken in disposing of infected material. The bull as a 

 carrier of infection probably does not play anything like the part he 

 was once assumed to. Usually by the time a cow comes into season 

 again after aborting, there is very little, if any, infection left in the 

 vagina or uterus, as secondary infections such as those caused by 

 ordinary pus-producing organisms rapidly take its place, and it has 

 been found impossible with the methods at our disposal to trace any 

 abortion infection in the uterus or vagina six weeks to two months 

 after an aboTtion. 



The bull may act in a mechanical way as an agent in transferring 

 infection from one cow to another, but probably plays no big role as 

 a spreader of infection. It would be unwise, however, to dismiss him 

 altogether as an infecting agency, as it has been found that in a small 

 proportion of cases bulls which have been exposed to abortion infection 

 do actually develop lesions of the genital tract. Several cases have 

 been reported from the United States of America of bulls which had 

 infection of the testicles and vesiculae seminales, the receptacles for 

 the semen after it is formed, but no experimental work had been done 

 to determine whether such bulls could infect cows. 



What part infected milk plays in the spread of infection, we do 

 not know yet, but it seems unlikely that it is a very important one. 

 It is possible that in a few cases the milker infects one cow from 

 another during the milking, as the disease can be produced by infect- 

 ing the uddeT through the teats, but usually it requires a large 

 quantity of infected material. The possibility of the foeces of calves 

 which drink infected milk being a source of infection has not been 

 experimentally determined, as it is practically impossible to isolate 

 the organism of abortion from a mixture of bacteria such as is found 

 in foeces. 



As regards the resistance of the causal organism of contagious 

 abortion to atmospheric conditions in South Africa, experiments are 

 at present in progress to determine this. Much difficulty has been 

 experienced in determining the presence of abortion organisms in a 

 mixture with others as well, and so far guinea-pig inoculation has 

 had to be relied on. The guinea-pig is susceptible to infection, and 

 can be used to isolate the abortion bacillus from contaminated 

 material, but, unfortunately, there are many organisms, in air and 

 soil, which rapidly kill guinea-pigs. The disease produced by the 

 abortion bacillus in guinea-pigs is a chronic one, and great enlarge- 

 ment of the spleen is usually the only lesion found M'hen the animals 



