The organism invades the uterus and attacks the early developing embryo causing death of the embryo with subsequent reabsorption or expulsion by abortion. If the resistance level is low, the process may have to repeat itself several times before the cow develops enough resistance to overcome the disease challenge. In this case, the cow may not be able to re-cycle and get bred during the breeding season, even a long breeding season. Some cows never are able to clear the infection, thus they will remain infected and serve as reservoirs of the disease. In some cases, especially with older bulls, the crypts and folds of the prepuce become contaminated with the organism and the bulls become permanently contaminated or infected.
Some bulls remain infected for years.
In the bull, there are no observable signs or lesions to indicate infection, but because of the strain of extra breeding, the bulls may show excessive fatigue, loss of condition, and decreased libido. The degree or severity of the reproductive problems seen in a vibrio infected herd depends upon the degree of resistance that a herd has developed against the disease. A review of the herd reproductive history is an important step toward determining if vibriosis is a problem in a herd. Herds with a long calving season or a decrease in calf crop are prime suspects for vibriosis. Without an elevated resistance to the disease, they are very susceptible to the disease and become easily infected when mating a contaminated bull.