Granular Venereal Disease of Cows 1085 



We have stated above that the comparative frequency of abor- 

 tion in affected herds is in harmony with the percentage of ani- 

 mals affected and the average virulence as revealed by the vulvar 

 lesions. This harmony is quite as well emphasized between the 

 various stables in this herd. The abortions have occurred in 

 those stables where the disease is most universal and the vulvar 

 lesions most intense. In the stable of 40 cows, with 98 % affected, 

 the abortion was decidedly the most severe in the herd. 



The observations relative to the variations in the prevalence of 

 abortion, in the different stables on this farm, bring up other in- 

 teresting questions. Of the 17.5% of apparently well females, 

 1 7 animals or 42. 5 % of those not showing vulvar lesions were virgin 

 heifers, so young that it is a fair assumption that they were free 

 essentially because they had thus far failed to become infected. 

 Of the remaining 23 apparently well females, 1 1, or 27.5%, were 

 adult cows in barn six ; and 8 others, or 20%, mostly adult and 

 aged cows, were in another barn. Thus, in a herd consisting 

 for the most part of young cows and heifers, there were 40 ap- 

 parently wellfemales, 42.5% of which were virgin heifers or heifer 

 calves, 47.5% adult or aged cows, and but 10% among the 

 young cows and heifers, which constitute the majority of the 

 herd. 



Two assumptions seem to be warranted by the observations in 

 this herd : 



1. As the cows grow old, and have been infected for several 

 years, they acquire an indefinite immunity from the effects of the 

 malady. The lesions become less intense, and abortion occurs 

 less frequently or is wholly absent. 



2. The cow may eventually recover spontaneously, and the 

 lesions disappear. This is in accord with the popular belief 

 relative to "contagious abortion ", whatever that term may mean. 

 It is commonly said that a cow aborts twice, and becomes im- 

 mune. While in this herd there are sufficient cases to disprove 

 this as a universal fact, there is much to support the rule. Sev- 

 eral important questions which repeatedly arise in reference to 

 spontaneous recovery may be tentatively answered by the observa- 

 tions in this herd. It is one thing for a cow to recover from the 

 disease and cease to be capable of transmitting it to other ani- 

 mals, and quite a different matter for her to cease to abort. 



