Mycobacterium paratuberculosis in the semen and genital organs of a semen-donor bull.

Mycobacterium paratuberculosis, the cause of Johne's disease, was isolated from the feces of a donor bull in an artificial insemination stud. During isolation and observation for 21 months, the organism was recovered from all of 26 fecal samples and from 8 of 31 semen samples. At necropsy, it was isolated from the intestine and adjacent lymph nodes, lung, spleen, seminal vesicles, and prostate gland but not from the testicles. We concluded that routine fecal cultures at bull studs will reveal infected bulls before they become genitally infected and shed M paratuberculosis in semen.