Blackleg (not hotlegs)

Blackleg, what? You mean black as in itim and leg as in hita?

This was  what I asked Dr. Bendicto Perez, our provincial veterinarian when I received a report from him that about 18 cows in San Nicolas have died recently due to this disease called blackleg.

Like me, you  might also want more information about blackleg.    I searched the internet, and I learned that blackleg is a disease of cattle, and to some extent, of sheep, caused by a  soil-borne  bacterium known as  Clostridium chauvei. The disease develops rapidly in affected animals and often death occurs before the owner has  even noticed any sickness in the herd.

Livestock owners should not assume they will not have blackleg losses simply because they never  had it  before. Since the causative bacteria are soil-borne, the disease may be introduced   into new areas in several ways, including windstorms, water-ways and wild animals.

Signs

Blackleg commonly occurs during  the warmer months young animals on pasture. Often  no symptoms are observed, but other times, one or more of the young calves show signs of illness by a high fever, lack of appetite, depression, lameness, and 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 sound is due to the gas under the skin which is produced by the growing bacteria. But as Dr. Perez  said,  the term blackleg  is s used because the most prevalent affected part of the animal’s body is its legs.

Postmortem changes

Putrefaction occurs rapidly in the carcass of an animal infected with blackleg 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 center  it may have undergone dry gangrene. It is unwise to cut open a swelling unless necessary for a diagnosis, as this increases the contamination of the soil.  

Treatment

If cases are noted in the early stages of infection, they may respond to immediate treatment with penicillin or other antibiotics in large doses. In recovered cases, the animal may be stiff in the leg, shoulder, etc., due to shrinking or thickening of the muscles.

Control and prevention

Because it is practically impossible to prevent animals from coming into contact with the disease, the chief control method for blackleg lies in building up resistance in the animals  using   a bacterin or   vaccine. The recommended procedure for vaccination  is the inoculation with bacterin of   young cattle between one and three months of age with a bacterin. A second injection of the bacterin should be given when an animal reaches six month sold.  To be on the safe side, and to ensure as permanent immunity as possible, all the cattle should be revaccinated annually until they are three years old. Routine vaccination procedures will vary with the type of livestock operation involved.

In case of an outbreak of blackleg in a herd, it is advisable to vaccinate or revaccinate, as the case may be, all of the animals with a recommended dose of the bacterin. As with other vaccines, there is a period of about two weeks following vaccination in which the animals have not built up a strong resistance to the disease. Losses may continue during this period, so it may be advisable to move the herd to another pasture after losses from blackleg occur and vaccination is carried out.

Sanitation

The bacteria that cause blackleg are capable of living in the soil. They have a capacity to form spores which can protect the organism from the effects of weather, and hence soil can remain infected for many years. Carcasses of animals affected by the disease are the chief source of soil infection. They harbor the germs in large numbers and liberate them from both artificial and natural body openings into the surrounding soil. For this reason, every dead animal should be promptly  burned or buried. The surface of the ground may be treated by burning it over with a heavy layer of straw, used oil, etc.