Blackleg is a frequent causes of sudden death in growing cattle. Hannah Noble spoke to a vet to find out more...
Blackleg, also known as blackquarter, quarter evil or quarter ill, is just one presentation of disease in cattle caused by a class of bacteria called clostridia.
There are several other forms of clostridial disease in cattle, such as black disease, tetanus and botulism.
Clostridium chauvoei, the specific bacteria which causes blackleg, is anaerobic and lives predominantly in soil and other organic matter.
CONTRACTING THE DISEASE AND RISK FACTORS
TIM Potter, a vet with Westpoint Vets, explains the bacteria is picked up from the environment.
He says: “The spores are usually in the soil or organic matter and are ingested by the animal.”
The risk often comes when cattle are exposed to spores in dirt or bare soil.
“If groundworks, such as drainage or fencing replacement, have taken place in fields where cattle are grazing, there is a risk animals may come in contact with the bacteria, especially inquisitive youngstock exploring in the dirt.
“There is a risk associated with the exposure of earth floors in buildings when they are being mucked out.
“Also, if you are harvesting and baling straw when it is muddy, there will be a risk of contaminating straw with soil, so when using it to feed cattle or as bedding there is a chance the clostridial spores will be present.
“Poaching around gates is also a risk factor which should be addressed.”
HOW IS ILLNESS CAUSED?
THE bacteria can be found anywhere in the body, but it tends to hone in on the biggest muscles which do the most work. These are usually in and around the legs, hence the name blackleg.
Dr Potter adds certain incidents, such as muscle damage, can kick-start the spores and rapid multiplication happens.
“Any muscle damage can break the dormancy of the spores, causing the bacteria to multiply rapidly and start producing toxins.
“We frequently see the disease emerge after handling cattle or on the back of some trauma to the muscles.
“Sometimes in bulling heifers when they have been riding each other, or around the neck from bashing into feed barriers and troughs.”
He adds that when the toxins are released they can cause dramatic effects and, most frequently, death.
PREVENTION AND TREATMENT
DR Potter says if there is an outbreak, the advice would be to put in place preventative measures and practice normal biosecurity.
“Vaccination is the key method of prevention. If or when you get the disease diagnosed on-farm, the investment should be put in place to vaccinate.
“The vaccine is comparably one of the cheapest on the market, one dose is about £1. But if this will prevent at least one death per year, it is cost-effective.”
He adds that minimising stress and trauma at handling is also important.
“You need to have good handling facilities, avoid rushing animals through to minimise any kind of bruising.”
He adds it is impossible to screen the entire environment, but it is important to minimise contact with spores where possible.
“Keep animals away from field works, especially younger, more curious stock. If you are digging drainage channels or replacing fences, try to keep the dirt contamination to a minimum.”
The illness can be treated with high doses of penicillin if picked up in the early stages. However, the response to treatment can be relatively poor.
HOW IS IT SPREAD?
BLACKLEG is not transmitted from one animal to another, but it is seen in groups of animals exposed to the same environmental conditions.
Dr Potter says: “There is also a risk spores can lay dormant in cattle brought onto the farm. It is a bug you are not going to keep out because it is in the environment and potentially carried as spores in animals.”
SIGNS AND SYMPTOMS
USUALLY the first sign of the disease is a dead animal and death is quick once the bacteria have begun to multiply.
However, Dr Potter explains that prior to death, the animal will generally appear dull and
depressed. It will usually be off its feed and often have a high temperature in excess of 41degC.
“If the bacteria has multiplied in one of the animal’s legs you often see sudden onset lameness and it will be severe. In the early stages, the muscle will be painful. In the late stages it is often cold to the touch, as the muscle is in effect dying off.
“If you get a serious outbreak you may have more than one animal affected or even more than one animal found dead.
“When investigated, we occasionally find signs of black, necrotic muscle in the legs, but the affected areas may be around the jaw or diaphragm. You can find it in any muscle, but usually the most dramatic signs are seen in the legs.
“The affected leg will tend to be swollen because of the large amount of gas produced by the bacteria. It often feels like bubble wrap and makes a crackling noise when touched. This is called crepitus.”