Blue-green algae toxicity

Attention! This is a potentially life-threatening condition for your Cow. Time is of the essence, contact your veterinarian immediately.

Blue-green Algae Toxicity

Cyanobacteria Toxicity

Blue-green algae, also known as cyanobacteria, are microorganisms that are similar to both bacteria and plants. They produce poisonous algae blooms containing cyanotoxins, which are secondary metabolites that are highly toxic to cattle. Although there are several types of cyanotoxins, they primarily affect the cow’s liver (microcystins, nodularins and cylindrospermopsins) or nervous system (anatoxins and saxitoxins).

Algae blooms occur worldwide in fresh and brackish water bodies, usually nutrient-rich, calm waters such as that found in ponds and dugouts. They can also occur in small stagnant water puddles or water troughs. They develop in warm sunny weather with temperature conditions ranging from 50 to 86°F (10 to 30°C), high phosphorus concentrations (over 30 micrograms/L), and high water nitrogen content.

Cattle are poisoned through drinking from contaminated water, usually from the windward side of stagnant water sources. Symptoms of poisoning vary depending on the type of toxin ingested.
  • Neurotoxic cyanotoxins: (associated with the nervous system) cause muscle tremors, decreased movement, difficulty breathing, convulsions, or in many cases sudden collapse and death.
  • Hepatotoxic cyanotoxins: (associated with the liver) will cause weakness, bloody diarrhea, pale colored mucous membranes, mental derangement, and eventually death.


Blue green staining
Difficulty breathing
Pale colored mucous membranes
Bloody diarrhea
Weight loss
Muscle tremors
Sudden death


  • History
  • Clinical signs
  • Physical exam
  • Water analysis for microcystins
  • Microscopic water and GI exam for cyanobacteria
  • Tissue analysis


Treatment TypeDetailsReference
Activated charcoal
Symptomatic and supportive care


  • Fence off downwind drinking areas where algae may be present
  • Add copper sulfate evenly to the water (the recommended maximum concentration in the water is 1 ppm, equivalent to 2.7 lb/acre-foot or 8 lbs per million gallons of water)
  • Regularly clean water troughs during humid conditions



Article Reference

Risk Factors

  • Algae growth in water trough
  • Access to a stagnant water source in pastures



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