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Back to Research & Development

Ovine brucellosis

Ovine brucellosis (OB) is a bacterial sheep disease characterised by infertility in rams. Infected rams produce semen of lower quality, making them sub-fertile or sterile. The effect on flock fertility depends on the percentage of infected rams and flock breeding management.

The effects of OB are often unrecognised, especially where marked fluctuations in fertility occur for other reasons.

Identification and diagnosis

Testicles should be firm and springy on palpation with no abnormal lumps and with scrotal circumference above 28cm. The lumps caused by OB are generally in the lower part of the testicle.

If your rams have abnormal lumps on their testicles, get a blood test to check for ovine brucellosis.


An integrated approach to prevent ovine brucellosis should consider the following:

  • only purchasing sires with an animal health statement from studs accredited as OB-free
  • developing and implementing a farm biosecurity plan
  • if not purchasing from accredited studs, keep newly purchased rams separate and test prior to mixing with your flock
  • keeping rams in small groups with the younger and older rams separated
  • isolating rams from ewes until their disease status is established as ewes can spread OB
  • palpating ram testicles to check for lumps prior to purchasing and before joining
  • seeking veterinary advice if you notice lower lambing percentages, longer lambing periods or abnormal lumps in the testes
  • establishing the OB status of your flock before introducing OB-free sires and maintaining ram-proof fences to avoid visits from your neighbours’ rams.