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(567) If drinking water becomes heavily contaminated with green and blue toxin producing algae, acute disease and high mortality can take place. Poisoning is only likely to be seen in pigs outdoors where there is access to ponds used as drinking water (unless of course indoor pigs derive their water from such sources). Large numbers of algae appear in the water during periods of warm sunny weather. Wind blows the organisms to the waters edge where they are ingested by the pig. The algae produce highly toxic substances that cause massive damage to the liver and haemorrhage and / or affect the nervous system causing coma and respiratory failure. Post mortem examinations show a grossly enlarged liver with haemorrhages.

Clinical signs

The onset of symptoms is usually sudden and within one to two hours. Death within 24 hours. Pigs show sudden collapse, muscle tremors, convulsions, discoloured skin and bloody diarrhoea.


A history of pigs having access to water showing evidence of algae blooms suggests poisoning. Clinical signs and post mortem examinations provide strong diagnostic evidence. A sample of the algae should be sent to a laboratory for identification and information sought on how to control it.


  • There is no specific treatment.
  • Give gastrointestinal absorbents such as charcoal and kaolin as a drench in water or in feed if practicable.
  • Pigs should be removed immediately from the source of water and housed away from sunlight in warm surroundings.
Management control and prevention
  • Provide an alternative source of water or if this is not possible install a fence to allow access to only a small area of the waterline. Protect this by a muslin barrier to hold back large numbers of the algae.
  • Multi-vitamin injections particularly the B complex may help.

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