476 MILK 



The germs of contagious abortion may live for weeks or months 

 outside of the body of the cow. Hadley states that it was iso- 

 lated from dead fetuses after five to nine months; from a calf 

 which had been frozen for twenty-four hours; and from uterine 

 discharges left on ice after seven months. It would seem likely 

 from these statements that pastures where infected cows graze 

 might harbor the infection, but the menace from this source is 

 probably small, since freezing and thawing rapidly disintegrate 

 bacteria. 



The virulence of Bacillus abortus varies considerably, a con- 

 sideration which accounts for the fact that some herds do not 

 suffer as seriously as others after the virus has been introduced. 



The bacillus is present in large numbers in the discharges 

 from the vagina of an affected cow and in aborted fetuses. Had- 

 ley states, "When not pregnant the udder is the only organ in the 

 body where abortion bacilli can live," and "there is proof that the 

 udder acts as a breeding ground for the germs." The abortion 

 bacillus carrier is, therefore, a prolific source of infection, and 

 introduction of a carrier into a sound herd is frequently the 

 means of infection. Such carriers are sometimes difficult to 

 detect, as they may calve normally. The infection is communi- 

 cated most readily immediately before and after abortion. 



Bulls may also become infected and then transmit the dis- 

 ease, but this is probably not as common as is generally believed. 

 According to Hadley, bulls are endowed with a sexual or individual 

 immunity, and are, consequently, less susceptible than cows. 

 The disease is milder in bulls than in cows, and the germs when 

 present in the body of a bull lose vitality in a relatively short time, 

 so that the bull becomes safe for service of non-infected cows. 



Contagious abortion may be transmitted through contami- 

 nated food and water and food poor in mineral matter, as, for 

 example, wheat rations which may predispose the animal to the 

 disease. Food is a menace chiefly when it is contaminated with 

 vaginal discharges of infected cows. In stables, therefore, where 

 animals are closely stalled the infection may spread rapidly and 

 movements of the cows may aid in disseminating the virus. The 

 common notion that moldy and decomposed grain or roughage 

 may be the cause of abortion is probably not true. 



The virus enters the body of the cow through the digestive 

 tract, the genital organs, and through a break in the skin or other 

 wound. The germs reach the uterus from any portal of entry, 

 as they seem to possess a selective attraction for this organ. 



Heifers are more susceptible to the disease than calves and 

 cows and are most commonly infected after the first calf is born, 

 while the womb is still open. A calf born from an infected cow is 



