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Vaccination 

Why vaccinate?

Vaccination is the key to preventing some of the most serious sheep diseases. Vaccination stimulates the body’s defence system to build immunity to a particular disease, by exposing sheep to either the live organism presented in a safe form  (e.g. Scabby Mouth vaccine) or to a killed organism (e.g. Blackleg vaccine) or to an inactivated organism (e.g. Johne’s disease vaccine) or to part of an organism (e.g. footrot vaccine, most Clostridia vaccines).

Indeed, without effective vaccines, the control, prevention and management of many diseases in the large vulnerable populations that make up sheep flocks would be virtually impossible. So what vaccines are available, how are they used and what are the diseases that they protect sheep against?

The Clostridia Diseases

The most widely used vaccine in Australia is a vaccine called ‘5 in 1’. It is used to control a group of potentially severe diseases caused by several different species of a bacterium called Clostridium. The important thing to remember with the Clostridia diseases is that they are not something that is caught. The organisms are either in the soil or in the sheep’s bowel. Sheep are therefore exposed to them or already have them in their system virtually all the time. It is only when some trigger compromises the ability of the sheep to resist disease that the sheep become sick. When the sheep become compromised, these bacteria produce potent toxins that cause severe disease and often kill the sheep within hours. There are six diseases that are caused by Clostridium bacteria for which vaccines are available. These are:- 

1/Pulpy kidney

Pulpy kidney is caused by a toxin produced by the bacteria Clostridium perfringens type D. The bacteria and the toxins they produce are present in the intestines of normal healthy sheep. The bacteria multiply slowly and are continuously swept out with the droppings so that the number of bacteria and the level of toxins never really build up. However, if there is highly nutritious food in the bowel as occurs if sheep are placed onto lush pastures or fed grain in higher levels than they are used to and the passage along the bowel slows, these bacteria are able to multiply quickly and produce lethal quantities of toxin. The toxin causes extensive damage to blood vessels throughout the body, including those in the kidneys (which makes them “pulpy” as they decompose after death) and also those in the brain. It is damage to the blood vessels in the brain that kills the sheep and is also the reason why they tend to die fairly quickly – often in hours, and also why there is no effective treatment. Essentially, these sheep have multiple “strokes”. The history of feeding lush food and symptoms displayed by the sheep arouse suspicions of this problem and it is confirmed by autopsy examination.

2/Tetanus

Tetanus is caused by a toxin produced by the bacterium Clostridium tetani. This bacterium survives in soil as spores wherever livestock are kept. These spores contaminate breaks in the skin such as those that occur with tail docking, grass seed penetration or an injury. Once in the body, if in healthy tissue the spores will sit there harmlessly, sometimes for months. If, however, the tissue is damaged, bruised or dead, the spores germinate, multiply and produce a toxin. The toxin then spreads to the nearest nerves and then to the spine and brain, causing a range of nervous symptoms

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