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Hot weather increases livestock-poisoning risk

Several advisories were posted in 
North Dakota this month

Hot weather and a stagnant water supply create prime conditions for cyanobacteria to form.

High temperatures promote the growth of blue-green algae, which can produce harmful toxins. Cyanobacteria, also known as blue-green algae, can produce toxins that are harmful to livestock, wildlife and people.

This month North Dakota Department of Health has posted blue-green algae advisories for four lakes. In addition, several water samples associated with the death of cattle and other animals that were submitted to the North Dakota State University Veterinary Diagnostic Laboratory have tested positive for cyanobacteria.

  • Read more: Testing livestock water quality critical during drought

“The growth of this bacteria is facilitated by the high temperatures common in July and August,” says Miranda Meehan, NDSU Extension livestock environmental stewardship specialist. “Blue-green algae often occurs in stagnant ponds or dugouts with elevated nutrient levels, forming large colonies that appear as scum on or just below the water surface. Live cyanobacterial blooms can be green, but also red or yellow, and often turn blue after the bloom dies and dries on the surface or shoreline.”

Some species of cyanobacteria can be toxic when livestock and wildlife ingest them. Toxicity is dependent on the species consuming the water, the concentration of the toxin or toxins and the amount of water ingested.

Cyanobacteria can produce neuro- and liver toxins. Signs of neurotoxin poisoning can appear within five minutes to up to several hours after ingestion. In animals, symptoms include weakness, staggering, muscle tremors, difficulty in breathing, convulsions and, ultimately, death.

Animals affected by liver toxins may exhibit weakness, pale-coloured mucous membranes, mental derangement, bloody diarrhea and, ultimately, death. Typically, livestock are found dead before producers observe symptoms. If cyanobacterial poisoning is suspected as the cause of death, producers should check the edges of ponds for dead wildlife.


  • Reduce nutrient levels entering the water source by implementing a nutrient management plan or establishing buffer strips with perennial plant species.
  • Create a designated drinking area where the risk of cyanobacteria is minimal. Fence off the pond and pump water from the pond to the water tank. Use water from other sources following periods of hot, dry weather.
  • Add copper sulphate to the water if the source has a history of algae blooms. Apply two pounds of copper sulphate per acre-foot of water, which is equal to a rate of eight pounds per one million gallons. Livestock must be fenced out of treated water sources for at least 10 days.

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