Student case report: Brucella ovis investigation in an accredited ram stud

Authors: Kater N
Publication: Grazing Gazette, Volume Issue 69, pp 6-12, May 2025
Publisher: Sheep and Beef Cattle Veterinarians Branch of the New Zealand Veterinary Association

Animal type: Sheep, Sheep - ram
Article class: Case Study

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Abstract:

Case history: A Brucella ovis free accredited stud consisting of 170 rising two-tooth Romney rams was visited to evaluate ram soundness and perform re-accreditation prior to ram sales in one month. Prior to this visit, all sire rams tested negative for B. ovis on the Complement Fixation Test (CFT) in March 2023. The stud had no previous history of B. ovis, and the risk of incursion was assessed as low.

Clinical findings: Five rams with epididymitis were tested for B. ovis using the CFT and one of the five rams tested positive (2/16). The B. ovis Enzyme-Linked Immunosorbent Assay (ELISA) was performed on the five samples and the CFT positive ram also tested weak positive (46). The four negative rams were culled. Seven days later the positive ram was re-tested and was negative on CFT and a weak positive on ELISA (46). Semen was also collected for microbiological culture which was negative for B.ovis, however heavy growth of Arcanobacter pluranimalium with some growth of Streptococcus uberis was found. The ELISA and CFT were repeated on the positive ram seven days later and he returned CFT positive (2/16) and weak positive (46) on the ELISA. The ram was euthanised for postmortem examination and microbiological culture of the reproductive tract. Examination revealed an atrophied left testicle with an encapsulated 3 cm diameter lesion near the left epididymal tail. The lesion contained purulent exudate and suppurative to caseous necrosis but did not communicate with surrounding structures. Samples from the lesion, ampullae, seminal vesicles, urinary bladder, and epididymides from both testicles were submitted for culture. While awaiting culture results, nine of the sale rams were tested using the CFT, all of which returned negative results. Culture results found scant mixed growth in the epididymides and lesion, while heavy growth of A. pluranimalium was isolated in the seminal vesicles, ampullae, and urinary bladder. B.ovis was not detected in any of the tissues. The ram was classified as a B. ovis false positive and the flock was reaccredited.

Clinical relevance: This case outlines the diagnostic process of a B. ovis investigation in an accredited ram stud.

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