Animal Health
Brucella ovis
Brucella ovis (B. ovis) is a bacterial disease of sheep that causes epididymitis and infertility in rams. If a ram battery is infected, flocks experience significant economic losses due to lost lamb crop, increased lambing interval, or rarely abortions. Rams become persistently infected and can transmit the bacteria to other rams in the flock for years. Ewes can become infected, but typically clear the infection within a breeding season.
Due to the economic losses associated with Brucella ovis, and how transmissible the bacteria is from ram to ram, Wyoming has regulations related to the disease. Additionally, testing of breeding rams may be required by other states for interstate movement. B. ovis is a reportable disease to the Wyoming Livestock Board.
Clinical Signs
In rams, clinical signs can include:
- Epididymitis
- Orchitis
- Poor quality semen
Rams can shed the bacteria even if they have no clinical signs. Diagnostic testing is required to classify the status of a ram.
In ewes, clinical signs can include:
- Decreased pregnancy rate
- Decreased lambing rate and low lamb crop
Transmission
Once infected, rams can shed Brucella ovis in urine and semen for years. Rams can shed the bacteria even if they have no clinical signs. Bacteria can be transmitted from ram to ram if an infected ram mounts a ewe and then another ram mounts the same ewe while the ewe is carrying the bacteria. Ewes can carry the bacteria in the vagina for a few months, but tend to have transient infections that clear within a breeding season. Brucella ovis can also be transmitted between rams through contact of infected urine or semen with mucous membranes (mouth, nose, prepuce, and eyes) and when rams mount each other.
Diagnosis
Serologic testing (such as the B. ovis ELISA test) detects the presence of antibodies to Brucella ovis in rams and is a common requirement for interstate movement or sale of breeding rams. Laboratories can report Brucella ovis ELISA results as negative, indeterminate, or positive. Rams with an indeterminate result should be handled like positive rams or have additional testing performed.
The Wyoming Livestock Board’s Chapter 12: Rules Governing Brucella ovis outline testing requirements for rams that have an indeterminate result or are exposed to infected rams.
Brucella ovis Certified Free Flock
The Wyoming Livestock Board has a Brucella ovis Certified Free Flock Program for sheep flocks. The requirements are summarized below. The application and renewal form for flocks interested in the program can be found here.
Initial Flock Certification Requirements:
- All rams six months of age and older must have two negative Brucella ovis tests performed 45 to 60 days apart.
- All rams must be officially identified
Annual Recertification Requirements:
- All rams six months of age and older have one negative B. ovis test within 60 days of the annual renewal date.
- Originate from a Certified B. ovis-free flock, OR
- Tested negative for B. ovis twice, 45 to 60 days apart, prior to entry into the flock
- Rams have not been in contact or commingled with sheep from any other source
- All rams must be officially identified
Control
Due to the devastating effect Brucella ovis can have on a flock, the Wyoming Livestock Board’s has rules governing the disease (Chapter 12: Rules Governing Brucella ovis). Rules related to control of Brucella ovis are summarized below.
- Test requirements for common grazing
- Non-virgin rams over 6 months of age shall test negative to Brucella ovis prior to turn out on common grazing lands
- Requirements for test-positive, test-indeterminate, and exposed rams
- Test-positive rams may not be sold for breeding purposes
- Test-indeterminate rams must be re-tested no earlier than 30 days after receiving indeterminate test results with a serum ELISA test or semen PCR test and determined negative for Brucella ovis before they may be sold for breeding
- Rams exposed to test-positive rams may not be sold for breeding purposes until they have tested negative for Brucella ovis on an approved test performed not less than 45 days after exposure
Test-positive rams should be isolated immediately and culled from the breeding flock. Test-indeterminate rams should be isolated immediately (separate from test-positive rams) and re-tested or culled from the breeding flock.
Prevention
Brucella ovis is mainly introduced into sheep flocks through infected rams. Preventing contact between disease-free flocks and sheep of unknown infection status is the most effective prevention measure. For new rams, it is recommended to perform a breeding soundness exam and Brucella ovis testing before the ram joins the flock. Preventing infection in ewes depends on controlling the disease in rams.
Reporting
Brucella ovis is a reportable disease in Wyoming. If the disease is diagnosed in a flock, the Wyoming Livestock Board should be contacted at 307-777-7515 or via the online reportable disease notification form.