196 COMMON AILMENTS OF CATTLE 



This is probably the chief way by which the disease disseminates, 

 as it is imposible to tell by a physical examination whether a 

 cow is diseased or not Milk from aborting cows may be a 

 carrier of the infection. 



Natural Mode of Infection. — The route by which the germ 

 gains entrance to the animal body is a debatable question. Some 

 authors hold that the open cervical canal at the time of oestrum is 

 the chief avenue of infection, being introduced into the cervix 

 and uterus at the time of copulation (breeding). ]STo doubt the 

 bull is responsible for the transmission of the disease in a great 

 many cases, especially is this true in herds where only one bull is 

 used, he being allowed to serve both diseased and healthy cows. 

 In abortion occurring among range cattle, the bull is probably 

 responsible for carrying the infection from one cow to another, 

 principally at the time of breeding. The digestive tube un- 

 doubtedly acts as one of the chief channels of entrance, the infec- 

 tion being obtained from contaminated feedstuff's, including 

 pastures where diseased animals are allowed to graze. Artifi- 

 cially the disease has been produced by injecting virulent abor- 

 tion bacilli into the veins and under the skin. It has been produced 

 by feeding infected material. Abortion has also been produced 

 by placing virulent material in the vagina of pregnant cows. 



Symptoms. — The period of incubation in infectious abortion 

 varies widely. In producing the disease experimentally certain 

 workers have determined the average period of incubation to be 

 approximately 130 days. The premonitory symptoms when 

 noticed consist of doughy swellings of the udder, and vulva, 

 followed by a mucus-like odorless discharge from the vagina. 

 The discharge may at times be streaked with blood, relaxation 

 of the sacro-sciatic ligaments, restlessness and stamping of the 

 hind feet. These symptoms usually appear one or two days 

 before the abortion occurs. Occasionally heifers have been ob- 

 served to make bag and even lactate at the fifth month of gesta- 

 tion, the abortion not taking place until the seventh month or 

 in its membranes, but when the abortion occurs after the fifth 

 and sixth months of gestation it is not always indicative of abor- 

 tion. Cows will be observed to abort suddenly without mani- 

 festing premonitory symptoms. When heifers or cows abort in 



