432 CHRONIC INFECTIOUS DISEASES 



or is eliminating the causal germ in her vaginal discharge 

 and milk. The tendency for cattle owners to dispose of 

 cows which have aborted insures a wide dissemination of the 

 disease. In rare instances the premises may become infected 

 through a contaminated bull to which the cows of the herd 

 have been brought for service. In still rarer instances a 

 very young calf from an infected mother may introduce the 

 infection. That persons, dogs, fowls, and birds of the air 

 may also carry infection from infected to non-infected 

 premises is probable. 



Symptoms. — The period of incubation following natural or 

 artificial inoculation is varied. It averages from natural 

 exposure about four months (33 to 230 days). Artificial 

 transmission of vaginal discharge from diseased to healthy 

 cows was followed by abortion in 9 to 21 days. The symp- 

 toms which indicate the presence of the disease in a cow 

 herd are: (a) A number of cows are dropping their calves 

 prematurely; (b) cows which have aborted show an abnormal 

 vaginal discharge, and (c) the appearance of symptoms of 

 premature labor, especially in heifers. 



The first few cases of abortion in a herd may be entirely 

 overlooked, as they are apt to happen during the first weeks 

 (five to seven) of pregnancy when the fetus is very smalL 

 A given cow may thus abort, be rebred, conceive and abort 

 again without the pwner's attention being attracted to the 

 condition. Finally after aborting twice or more times she 

 may carry to full term and be delivered of a viable, fully 

 developed calf. Such a cow is spoken of as an "immune" in 

 the sense that she will not abort again, although she is still 

 diseased and can infect other cows. Abortion seems most 

 common in the fifth to seventh months of pregnancy, usually 

 occurring on or about the 190th day, but varying from the 

 149th to the 254th day. Quite often before the actual 

 abortion occurs the cow shows prodromal symptoms such as 

 filling of the udder, edema of the vulva, colostral milk, 

 sinking on each side of the tail-root, congestion of the vaginal 

 mucosa and the discharge of a reddish or yellow odorless, 

 viscid fluid. The expulsion of the uterine contents usually 

 occurs, however, without marked labor pains and the fetus 



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