156 DAIRY FARMING 



tagious and may spread through a herd from a single in- 

 fected animal brought into the herd. From 50 to 75 per 

 cent of the cows in an affected herd often abort. The 

 remainder are either naturally immune or carry the calf to 

 full time in spite of the disease. The calf is usually born at 

 the sixth or seventh month and, at this early stage, always 

 dead. After having once aborted many of the cows are 

 immune and afterwards carry the calf in a normal manner. 

 Others abort twice before becoming immune. Some as the 

 result of abortion become sterile or shy breeders. The 

 disease is spread either by the male or by the germs from 

 an affected animal getting on the feed consumed by another. 



Two methods of testing cows for infection with this dis- 

 ease have recently been devised. These methods as yet 

 can be carried out only by a skillful operator supplied with 

 the facilities of a scientific laboratory. It is probable that 

 these methods will be adapted for use by a large number of 

 veterinarians. Such a test may make it possible to keep 

 herds free from abortion by excluding animals having the 

 disease. 



No satisfactory treatment has yet been discovered for 

 contagious abortion. The main precaution now is preven- 

 tion as far as possible by keeping the disease out of the herd. 

 It is not safe to buy an aged bull or a cow from a herd where 

 the disease exists. If an abortion occurs, the fetus and after- 

 birth should be burned or buried. The aborting cow should 

 be isolated and the stall where she stood disinfected with a 

 5 per cent solution of carbolic acid. 



144. Tuberculosis. This disease is caused by a certain 

 species of bacteria. The bacteria cannot develop from the 

 surroundings or conditions of handling, but must come from 

 another animal having the disease. The germs that cause 



