Blackleg is a soil-borne disease

Gary Sliworsky
Ag. Rep.

Blackleg is a disease of cattle, and less frequently of sheep, caused by a soil-borne bacterium. The disease develops rapidly in affected animals and often death occurs before the owner has noticed any sickness in the herd.
Most parts of Ontario are affected by blackleg, but new out-breaks are found almost yearly in areas where the disease has not previously been reported. For this reason, livestock owners should not assume they will not have blackleg losses simply because they never have before. Because the causative bacteria are soil-borne, the disease may be introduced to new areas in several ways, including windstorms, waterways and wild animals. The bacteria is capable of living in the soil, and the spores can remain in the soil for many years.
Calves and yearlings are most often affected. Often no symptoms are observed; the animals are found dead on the pasture with no previous signs of illness. At other times, one or more of the young calves show signs of illness which include swellings that appear in the muscles on various parts of the body. Sometimes the leg muscles are involved, or the muscles in the region of the back, hip, flank, chest or shoulder. In the latter stage of the disease, these swellings spread and become quite mushy, producing a characteristic crackling sound when pressed with the hand. This is due to the gas under the skin which is produced by the growing bacteria.
Putrefaction occurs rapidly in the carcass of an infected animal and results in a typical bloated appearance of the carcass soon after death. The legs are extended stiffly and a frothy, bloody discharge is often apparent at the anus and the nostrils. The skin over the swelling is usually normal but in the centre it may have undergone dry gangrene. When cut open and examined, the swellings are usually found to contain discolored serum and gas. When affected muscles are cut open, they are usually found swollen an either black or darker in color than normal, with gas present. It is unwise to cut open a swelling unless necessary for a diagnosis, as this increases the contamination of the soil.
Livestock owners should familiarize themselves with the signs of this dangerous and costly disease, so that cases are not ignored or passed off as bloat. A vet should be called to make an accurate diagnosis as soon as possible. A wrong diagnosis, or no diagnosis, could be serious and expensive because more animals may become infected and result in heavy losses in the herd. It is often difficult to make an exact diagnosis in the field because of the similarity of the sign of blackleg to certain other diseases.
Reminder
Producers who need to renew or apply for a Grower Pesticide Safety Certificate should call 1-800-652-8573 as soon as possible.