476 CHRONIC INFECTIOUS DISEASES 



Aborting herds should not be allowed to exhibit at fairs or 

 cattle shows which is a common way of distributing the 

 virus of the disease. 



Cows which have aborted should not be sold but kept 

 in the herd until they become "ceased aborters," unless 

 they fail to conceive when bred. Keeping together the 

 original herd will lead to a more rapid eradication of the 

 disease than if the infected animals are sold and replaced 

 with new, susceptible ones. 



Immunization.-^Hecent investigations point to the prob- 

 ability of immunizing cattle against infectious abortion. 

 Repeated intravenous injections of living cultures in 10 c.c. 

 doses two months before conception, were employed with 

 the result that the fetus was carried to full term. The effect 

 of the vaccination on the animal, however, was not favorable. 

 Later attenuated cultures were used with partial success. In 

 England experiments with 150 c.c. of a virulent culture in- 

 jected two months before breeding gave encouraging results. 



INFECTIOUS ABORTION OF MARES. 



Definition. — Infectious abortion of the mare, differing from 

 the cow, is an acute disease, probably a septicemia. It is 

 characterized by the premature delivery of the foal, or, if 

 the pregnancy is completed, by the birth of a colt unable to 

 stand and nurse and which soon dies. 



Occurrence. — Infectious abortion of mares was not recog- 

 nized in this country until 1886. In that year in one county 

 in Illinois twenty-five hundred foals, valued at $150,000, were 

 lost through it. The disease is now widely distributed, but 

 obviously attracts more attention in studs where a large 

 number of foals is lost on a single farm. Isolated cases may 

 escape unnoticed. 



Etiology. — According to Ostertag abortion in mares is 

 caused by a Gram-negative streptococcus. From the investi- 

 gations of Good and of Meyers, substantiated by Schofield, 

 it would seem that the outbreaks in America are produced 

 by a specific bacillus which has been isolated from a number 

 of different studs of aborting mares and one stud of aborting 



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