200 COMMON AILMENTS OF CATTLE 



ylene blue have been used extensively in the treatment of abor- 

 tion. Good results reported from the use of these drugs is 

 probably due to the increased resistance or immunity to the 

 disease which occurs after one or two abortions rather than the 

 effects of the remedies themselves. 



Immunization. — Cows after aborting once or twice become 

 more resistant to the disease and carry the calf to the normal 

 termination of pregnancy. In this way the disease will gradu- 

 ally exhaust itself, providing susceptible animals are not added to 

 the herd. Because of the tendency toward natural immunity the 

 problem of producing an artificial immunity presented itself. 

 Living and dead cultures of abortion bacilli are being used in an 

 attempt to produce artificial immunity in young heifers. 



MILK FEVER (PARTURIENT PARESIS ) 



This is a disease peculiar to the cow, occurring at or near 

 the time of calving. This disease as a rule confines itself almost 

 entirely to the heavy milking breeds. Generally cows are 

 afflicted at the third to fifth birth, although it may occur in 

 cows bearing their first calf. Most cases occur during hot 

 weather, and during rapid changes of weather. It may appear 

 also during the coldest weather. Milk fever usually sets in from 

 24 to 48 hours after birth of the calf, the maximum interval 

 being several days. It rarely occurs at the time of birth. Iso- 

 lated cases have been observed just before calving, but never 

 before the secretion of milk had begun. 



Predisposing Causes. — Confinement in the stall predisposes 

 to milk fever, partly because of lack of exercise, which is very 

 essential in cows that are highly fed, and partly because of the 

 air being hotter and at times impure. 



Constipation may become an accessory cause by increasing 

 the volume and density of the blood with certain material that 

 should pass off by the bowels. 



Mature age is a strong predisposing cause. The disease 

 seldom, if ever, occurs with the first parturition and rarely with 

 the second. It appears with the third, fourth, or fifth birth, 

 when the cow has attained her normal growth and is converging 

 all of her energies to the production of milk. 



