Brucellosis in Sheep: Abortion, Ram Fertility Problems, and Zoonotic Risk

Brucellosis in sheep is a bacterial reproductive disease most commonly associated with Brucella ovis. In sheep, it mainly affects the reproductive tract of rams, causing epididymitis and orchitis that can lower fertility. Ewes may be affected less often, but placentitis, abortion, and perinatal lamb loss can occur.

One reason this disease is frustrating is that infected rams do not always look obviously sick. Some have palpable scrotal changes, while others mainly show poor semen quality or reduced breeding performance. Infection can persist for years, and rams may shed the organism intermittently in semen.

In the United States, B. ovis infection is considered rare, but it remains important because even a small number of infected breeding animals can affect flock fertility and replacement plans. Your vet will usually approach this as a herd health and biosecurity issue, not only an individual-animal problem.

There is also a human health angle. While B. ovis is not considered the main human brucellosis threat, Brucella bacteria as a group are zoonotic, and people can be exposed through contact with infected birth products, reproductive fluids, semen, blood, or unpasteurized dairy products. That is why careful handling and reporting matter.

Brucellosis in sheep is caused by bacteria in the genus Brucella. The species most associated with ovine reproductive disease is Brucella ovis. This organism spreads mainly among rams through direct contact, including mounting behavior, and can also spread through breeding. Ewes can become infected after mating with infected rams, although active infection in ewes is less common.

The bacteria are shed in reproductive fluids, especially semen, and Brucella organisms more broadly can also be present in placentas, fetuses, vaginal discharge, urine, and milk. That means lambing areas, abortion materials, handling equipment, and contaminated clothing can all matter from a biosecurity standpoint.

Risk goes up when new breeding animals are introduced without testing or quarantine, when older and younger rams are mixed, or when flock fertility problems are missed for more than one breeding cycle. APHIS biosecurity guidance for sheep and goats recommends maintaining a closed flock when possible and quarantining additions for at least 30 days.

Not every ram with epididymitis has brucellosis, and not every abortion storm in sheep is caused by Brucella. Your vet may also consider other infectious and noninfectious causes of infertility and abortion while working through the diagnosis.

Diagnosis usually starts with a careful breeding history and physical exam. Your vet may palpate the scrotum and epididymides, look for asymmetry, thickening, or nodules, and review conception rates, semen quality, abortion history, and ram age structure in the flock.

Because some infected rams have no obvious lesions, testing matters. Merck notes that rams in an infected flock should be examined repeatedly with scrotal palpation and serologic testing. Tests used in control and certification programs include indirect ELISA, complement fixation, hemagglutination inhibition, indirect agglutination, and gel diffusion. Semen culture may help identify intermittent shedders, though repeated sampling can be needed.

Your vet may submit samples through an APHIS-approved laboratory, since USDA maintains approved testing pathways for Brucella ovis. In some cases, additional testing such as culture or organism detection on reproductive tissues may be considered, especially when abortion material or semen samples are available.

A single negative result does not always clear a flock concern. In eradication programs, repeated testing over time is often needed, and confidence improves after two consecutive negative tests performed 30 to 90 days after the last infected ram is removed. Your vet can help build a practical testing plan that fits your flock size and breeding calendar.

Prevention starts with biosecurity. The safest plan is a closed flock when possible. If you need to bring in new sheep, APHIS recommends buying healthy animals that have been recently inspected and keeping them separate for at least 30 days. For breeding rams, your vet may advise pre-purchase exams, scrotal palpation, and serologic testing before they join the flock.

Regular ram checks matter. Merck recommends repeated scrotal palpation and serologic testing in infected flocks, and routine pre-breeding exams can help catch genital abnormalities before they affect conception rates. Keeping younger rams separate from older, potentially infected rams may also reduce spread.

Lambing and abortion hygiene are also important. Wear gloves, protective clothing, and eye protection when handling placentas, aborted fetuses, vaginal discharge, semen, or contaminated bedding. Clean and disinfect equipment, isolate affected animals, and dispose of reproductive waste safely according to your vet's advice and local rules.

To reduce human risk, avoid raw milk and unpasteurized dairy products, and keep children, pregnant people, and immunocompromised individuals away from abortion materials and lambing areas when disease is suspected. There is no recommended vaccination for B. ovis in the United States, so prevention relies on testing, sourcing, quarantine, sanitation, and flock management.