Botulism is a paralytic neuromuscular disease caused by the ingestion of potent neurotoxins released by Clostridium botulinum bacteria.
The bacteria grow in decomposing animal carcases or decaying plant material, and during peak toxicity ingesting only a few grams of infected material can be enough to kill a cow.
Toxins are not contained to carcases and can leach into surrounding feed or water.
Not all carcases will carry botulism, but in the right (or wrong) circumstances a single carcase can cause a huge amount of damage.
There are two main ways in which cattle are likely to ingest botulinum toxin:
1. Protein or phosphorus deficiency can result in carrion eating or bone chewing, particularly in cattle in northern parts of Australia during dry seasons.
2. When stock feed or water is contaminated with the toxin, large numbers of animals can be exposed. Carcases in water sources can cause outbreaks, as can feeding mouldy spoiled silage, hay made during rodent plagues, or poultry litter.
Clostridium botulinum thrives best in warm, moist, anaerobic conditions, which can make silage the perfect environment for growth.
When cattle are fed bales in the paddock for instance, they are unlikely to ingest a contaminated section as they can see, smell and selectively avoid it. At worst, a small number of animals may ingest a toxic dose.
Mixer wagons, however, amplify the risk of outbreaks significantly. A small area of contamination within a bale or stack can be chopped and dispersed through an entire load and become undetectable to cattle.
Botulism can affect cattle of any breed or age. Regional climate is not considered a risk factor.
Signs and severity of botulism depend on the amount of toxin ingested, but can include:
● Sudden death.
● Progressive muscle weakness leading to complete paralysis, respiratory failure and death.
● Weak down cows (often unable to raise their heads).
● Flaccid paralysis of the tongue and jaw (tongue will often hang out).
● Inability to eat, drink or swallow.
● Paralysis of the tail.
● Restlessness, incoordination.
● Reduced appetite.
● Dehydration and sunken eyes.
● Constipation.
● Weakness.
After ingestion of the toxin, signs can occur within as little as 12 hours but can also take up to three weeks to present.
If you suspect the disease in any of your livestock, contact your vet immediately.
Diagnosis is usually made based on history and typical clinical signs. Specific tests to detect the presence of botulism toxins are currently expensive, complicated and unreliable.
There is no treatment specifically for botulism. If cattle are affected so badly that they cannot stand or signs progress rapidly, death is inevitable and they should be humanely euthanased as soon as possible.
Mildly affected cattle require gold-standard nursing to avoid secondary complications.
Prevention is possible through annual herd vaccination.
Your regular veterinarian will be able to help you determine your herd’s level of risk. All farms using mixer wagons should strongly consider vaccination.
There are several vaccines available, so it’s best to speak with your vet to determine the optimal product and strategy for your farm.
The author has no affiliations (financial or otherwise) with any botulism vaccine manufacturers.
Lucy Collins is completing her Dairy Residency with The University of Melbourne. She works as a dairy veterinarian for Apiam Animal Health and alongside her partner on his family’s dairy farm in south-west Victoria. She is a 2021 Nuffield Scholar supported by Gardiner Dairy Foundation.