Dr Cave said OB is a bacterial disease which is characterised by infertility in rams and unlike brucellosis in cattle, which Australia is now officially free of. 

“As a result of its effect on rams, OB may cause reduced lamb marking percentages, an extended lambing period, ill thrift in newborn lambs and increased culling of rams due to infertility,” Dr Cave said.

“In some cases, the presence of OB in a flock may be insidious and go unrecognised due to other causes of poor lamb marking percentages. However, once a number of rams are infected OB can lead to a substantial loss in production,” he said.

Dr Cave said OB causes inflammation of the epididymis, which is the tube in which semen is transported from the testis. This inflammation leads to a complete or partial blockage of the epididymis, leaving the ram sterile or sub-fertile. 

“One way of diagnosing OB is to palpate or feel the testis of a ram for swellings, it can also be diagnosed by a blood test or by semen examination. 

“OB is typically introduced into a flock by an infected ram. The disease subsequently spreads ram to ram or via ewes during joining.” 

He said once introduced, to avoid the adverse effects of OB, the only solution is to eradicate the disease, which is achieved with veterinary assistance by palpating and blood testing rams, and culling any that are found to be infected. 

“As always, prevention is better than cure. To assist in identifying low risk flocks a voluntary accreditation scheme is in place. 

“Your property can become OB accredited in consultation with your private veterinary practitioner by successively testing all rams over six months of age with negative results and demonstrating secure boundary fencing.” 

Dr Cave said when purchasing replacement rams, always purchase from an OB accredited flock and this will provide the safest ‘risk’. In addition, boundary fencing should be sound and secure to prevent straying animals from neighbouring properties. 

For further advice contact your local veterinarian or Agriculture Victoria veterinary or animal health officer.