Risk of poisoning by blue-green algae
All animals, including people and farm dogs, are at risk of poisoning from blue-green algae. Sheep are more likely to be affected than cattle because they tend to drink from the dam edges, while cattle often wade into the dam beyond the more toxic margin.
Toxicity can change rapidly and can increase as a bloom ages or starts to die. Some toxins persist for more than 3 months before being degraded by sunlight and microbial activity. Water can be toxic to stock even after the bloom has disappeared. Sun-dried algal scum can remain toxic to animals for up to 5 months.
Signs of blue-green algae poisoning when neurotoxins are involved
Signs can include:
- dead livestock found close to water supply
- muscle tremors, staggers and convulsions
- death within 24 hours of first signs.
Signs of blue-green algae poisoning when liver toxins are involved
Signs can include:
- ill-thrift and scouring
- photosensitisation – pale, bare areas of skin, particularly around the head, become swollen and red, followed by erosions and scab formation
- deaths can occur 1–2 weeks after ingestion.
Treating poisoned livestock
If blue-green algae poisoning is suspected, immediately remove livestock from the contaminated water supply. There is no specific treatment for livestock showing signs of blue-green algae poisoning. Activated charcoal or bentonite can be used before signs develop to prevent further absorption of the toxin, but are expensive and only an option for valuable livestock.
Diseases which may look like blue-green algae poisoning
- anthrax (reportable disease)
- pulpy kidney
Call a veterinarian when high stock losses occur.
The signs of blue-green algae poisoning can be similar to other livestock diseases that are reportable. Always ask your veterinarian to investigate whenever sudden death and high death rates occur in livestock. Blue-green algae poisoning can have similar signs to anthrax, which is a reportable disease with human health risks and potential to adversely affect some export markets if not contained rapidly.
If you see unusual disease signs in your stock, call your private veterinarian, a veterinary officer at the Department of Primary Industries and Regional Development (see the Livestock biosecurity contacts page), or the Emergency Animal Disease hotline on 1800 675 888.
Preventing poisoning by blue-green algae
It is possible to reduce the likelihood of blue-green algae developing in farm water supplies. Regular sampling of susceptible supplies will help identify the early stages of algae growth, and early treatment is much more successful in preventing blue-green algae growth and poisoning.
See Managing blue-green algae on farms in Western Australia for details.