Botulism is caused by a potent nerve toxin produced by the anaerobic bacteria Chlostridium botulinum and is a paralysing disease of humans, animals, and birds (NSW Department of Primary Industries, 2021). Botulism is widespread and is a disease considered to be of economic importance in beef cattle in Australia (especially Northern Australia) as it has a rapid onset and is usually fatal. All animals are predisposed to the condition if they happen to eat toxin-containing food. Common sources of ingestion of the Botulinum toxin include animal carcasses, rotting organic matter and poorly prepared silage. Treatment is rarely attempted but there is a vaccine available for the prevention of botulism in cattle.
The cause of botulism is from poisoning due to the neurotoxin produced by Clostridium botulinum. The bacteria produce one of several types of toxins, designated botulinum A through to G with most outbreaks in cattle and sheep in Australia due to Type C or D (NSW Department of Primary Industries, 2021). The bacteria are commonly found in soil, marine sediments, and water around the world, but they are also a normal inhabitant of the gastrointestinal tract of healthy horses, poultry, and cattle.
Clostridial bacteria produce long-lived spores that ensure their survival in the environment. The bacteria that produce the condition will only grow when moisture and warmth are present and when there is a restriction in oxygen supply. Conditions ideal for the growth of Clostridium botulinum are provided by mouldy hay, chaff, silage, decomposing grass, dead carcases and in water where carcases or other organic matter are present.
Botulinum toxin is often reported as being one of the most potent toxins known to mankind, as only a miniscule dose is required to be fatal. Heat treatment to 100°C for ten minutes is required to destroy the toxin and the spores are even more resistant, requiring 120°C for ten minutes or more before they are destroyed (Hungerford, 1990).
Nearly all cases of botulism in livestock are caused by ingesting the established toxin rather than the bacteria multiplying in the gastrointestinal tract. The disease occurs throughout Australia with outbreaks being associated with (Besier, 2021):
- Bone chewing – Usually caused by a phosphorus deficiency. Many Australian soils are derived from parent material that is low in phosphorus and to help satisfy their craving for phosphorus (or protein), cattle will chew on bones and carrion (commonly contaminated with the botulinum toxin).
- The consumption of contaminated feed or water from rotting organic matter containing the toxin. Eating mouldy cereal, hay and chaff have often been implicated in outbreaks and improperly made silage that rots instead of fermenting is an ideal breeding ground for botulism if spores are present.
- The very rare disease in which C botulinum grows in the tissues of a living animal producing toxins is called toxicoinfectious botulism (Kahn, 2005).
Signs, Symptoms And Diagnosis
The botulinum toxin binds strongly to nerve endings, preventing nerve impulses progressing to muscles and animals with botulism are typically observed in a floppy or flaccid state because they can’t move their muscles
Livestock of all ages can be affected, and generally symptoms include (Hungerford, 1990) (Besier, 2021):
- Not eating or drinking
- Unable to control or withdraw the tongue with it hanging out of mouth
- Shallow, abdominal breathing
- Lassitude (lack of energy)
- Staggering gait, circling, arching the back
- Urinary incontinence
- Recumbency (lying down)
- Limberneck which is the extension of the head when lying down
- Progressive motor paralysis
- Disturbed vision
- Drooling with difficulty chewing and swallowing
- Death (usually due to cardiac or respiratory paralysis)
Clinical signs are usually observed from 2-6 days after the ingestion of contaminated food, with the disease likely being fatal once symptoms occur. The observed signs frequently follow in this order in cattle: loss of appetite for food or water; ceasing rumination; staggering; recumbency with the animal lying on their brisket with their hind legs stretched out behind them. Cattle affected with botulism do not develop a fever and do not respond to treatment for other causes of “downer cow syndrome” like milk fever and three-day sickness (Qld Government Department of Agriculture and Fisheries, 2013).
Typically, there are no characteristic post-mortem changes in the organs, but the tongue is usually found protruding between the incisor teeth, and the presence of food is often found in the lips, throat, and gullet.
Examining the signs suggestive of the disease and the absence of other possible causes is how botulism is diagnosed. Isolating the toxin from bowel contents is quite often impossible and Hungerford (1990) suggests the following features assist a clinical diagnosis:
- History of deficiency in phosphorus or protein, access to contaminated bones, feed, decaying carcasses, or other matter
- Typical symptoms in other affected cattle
- Absence of lesions of other disease at post-mortem
- Presence of sugar in the urine
- Control of the disease following vaccination (in cattle)
Any dietary deficiencies in grazing animals should be corrected and, if possible, the removal of possible contaminants such as carcasses, spoiled feed and decaying grass should be undertaken. When purchasing feed look for quality ingredients that are free of botulinum toxin. Quality assurance systems are now implemented in most commercial feedlots and dairies minimising the risk of using contaminated feed. Effective vermin control measures during the preparation and storage of feed products are very important in the prevention of botulism.
An effective long-term strategy in the prevention of botulism is by vaccination with one of the botulinum vaccines available on the market. Whenever possible, cattle should be vaccinated well before any suspected risk period and all vaccines require boosters to be given to maintain protective levels of immunity.
Most importantly, the correction of any nutrient deficiencies, but specifically of phosphorus, will help prevent bone chewing, and supplementation with MegaMin Extra Phos 8 should be used in deficient country in conjunction with appropriate vaccination programs. Addressing nutritional deficiencies not only helps minimise risk of disease but often comes with the added benefit of improvements in production. MegaMin Livestock Supplements offer a range of quality broad spectrum mineral products that are tailored to maximise optimal growth, health, and performance of livestock in a vast range of feeding situations and environmental conditions.
Botulism is a disease that can have a serious economic impact with outbreaks sometimes resulting in massive herd losses. To reduce the risk of botulism outbreaks, good management strategies must be commenced with quality control of feedstuffs, vermin control, removal of carcasses from paddocks and watering points. Most importantly for botulism prevention is the elimination of nutrient deficiencies via supplementation, in conjunction with an appropriate vaccination program.