Blackleg is a generally fatal bacterial disease of young cattle and sheep of any age.
Blackleg is caused in most cases by the bacterium, Clostridium chauvoei.
The disease usually causes lameness due localised inflammation of muscle with heat, swelling and gas formation (gas gangrene). This is followed by a generalised toxaemia or poisoning of the animal causing rapid death.
The bacterial spores can survive in soil for many years. Spores are ingested from pasture by the animal, they then enter the bloodstream and lodge in muscle where they can remain dormant without causing ill-effect.
Blackleg in sheep is frequently associated with wounding as a result of shearing, tail docking, castration, injury to ewes at lambing or infection of the navel soon after birth. In cattle, unknown 'triggering' factors cause the organism to germinate, multiply and cause the onset of blackleg although outbreaks following handling and associated bruising are common. The disease is more commonly seen in young, rapidly growing cattle or cattle on a high plane of nutrition. The organism has been documented to also damage heart muscle and diaphragm resulting in clinical signs not usually associated with this disease.