Ovine brucellosis is an infection which causes disease and infertility in sheep. The prevalence of infection can be high if the disease is not controlled. Merinos show a lower incidence of disease compared to British breeds and crossbreds.
This form of brucellosis does not affect people.
Ovine brucellosis is present in Australia.
It has been reported in most major sheep-producing regions of the world and is present in Australia, New Zealand, the United States, South Africa and Europe.
Ovine brucellosis has not been reported in the United Kingdom.
The first sign of disease in a ram is:
- lower quality semen - acute oedema and inflammation of the scrotum may follow
- a mild systemic reaction, including fever and depression may occur
- palpable lesions develop in the epididymis and tunica of one or both testicles after about 9 weeks.
Affected rams have normal libido but reduced fertility to complete sterility.
When the number of affected rams in a flock is greater than about 10%, the fertility of the flock is appreciably decreased.
There are usually no clinical signs in the ewe but in some flocks, infection causes abortion or the birth of weak or stillborn lambs, associated with a placentitis.
The consequences of infection in a flock are largely seen as a drop in flock fertility.
How it is spread
The infected ram is the source of infection and perpetuates the disease in a flock. The excretion of B. ovis in the semen of infected rams is thought to continue indefinitely until the testicle becomes completely fibrosed. The main method of transmission is from ram to ram via the ewe's vagina during the mating season. During the non-breeding season spread can occur between rams when mounting each other or licking each other's prepuce.
Infection in ewes is short-lived but will persist in a few animals. Nevertheless, spread between ewes has not been noted. Lambs born to infected ewes and drinking their milk do not become infected.
The organism can survive on pasture for some months but this is not important in the spread of the disease.
Monitoring and action
The palpation of both testicles from behind will detect the lesions associated with brucellosis.
Blood samples may be collected for a complement fixation test (CFT). Where lesions are present in rams, sterile samples of epididymis, accessory glands and testicle can be taken at post-mortem for bacterial culture. Semen samples collected by electro-ejaculation can be examined for semen quality or cultured.
Owners of commercial flocks should purchase rams from studs that are accredited under the Ovine Brucellosis Accreditation Scheme.
Good management of the rams will keep the disease at a low level.
Good fences are important in keeping neighbouring rams out.
Virgin rams and those known to be free of infection should be kept separate from older rams or those suspected of being infected.
All rams should be palpated every 6 months and those with palpable lesions of the reproductive organs should be culled.
Individual treatment is not a suitable option.
Vaccination is not available in Australia.
- Last reviewed: 31 Jan 2018
- Last updated: 31 Jan 2018