Blue-green algae and livestock

Farm Forum

BROOKINGS, S.D. – Recently there have been concerns about algae blooms on stock dams. The predominant question is ‘Do I need to be concerned about my livestock?’

The answer is maybe, said Adele Harty, SDSU Extension Cow/Calf Field Specialist.

“With the recent warmer temperatures, the conditions are right for blue-green algae blooms,” she said. “The different species of blue-green algae contain various toxins, which can poison livestock, resulting in rapid death.”

Blue-green algae does not look like traditional green algae, that typically forms in a mat, but rather it can appear like small grains of green sand at the water surface.

There are different types of blue-green algae that also have varying appearances. Some may resemble spilled paint around the edge of the stock dam, some will give the entire water source a pea-green appearance, while others will have a teal green appearance.

Harty explained that blue-green algae blooms when weather is hot and winds are calm. As the algae begin to die, gas is produced in the cells causing the colonies to float to the water surface. “The wind blows the algae blooms to the shorelines resulting in their concentration and easy access to livestock,” Harty said.

She added that identification of blue-green algae blooms in water can be difficult because the blooms appear and disappear rapidly.

These blue-green algae blooms can contain neurotoxins (nervous system damage) or hepatotoxins (liver damage), depending on the type of blue-green algae present. “If water containing blue-green algae is consumed by livestock, death will typically occur within 24 hours or less after ingestion,” she said. “Cattle, sheep, horses and small animals are all susceptible to these toxins, as well as humans!”

Due to the rapid advancement to death, Harty said the observation of clinical signs including tremors, paralysis, respiratory failure, diarrhea, and salivation, are not often seen. “The most frequent indicator of toxicity from blue-green algae is to find a dead animal close to the contaminated water,” she said.

If the animal survives initial poisoning, photosensitization (sunburn) will be noticeable, however Harty said the animal will likely die later due to liver failure.

Unfortunately, there is not a typical treatment for blue-green algae toxicity due to the rapid progression to death.

“If you suspect that you have lost livestock to blue-green algae toxicity, work with your veterinarian to collect the appropriate samples to confirm or deny the blue-green algae toxicity,” Harty said.

A complete set of tissues (liver, brain, stomach contents) and a water sample is needed for diagnosis.

Collecting water samples

Water samples should be taken from concentrated areas. The diagnostic lab requires two water samples; 10 milliliters of water mixed with 10 milliliters of 10 percent formalin, and a quart of frozen water.

Your local veterinarian can then submit the samples to the SDSU Animal Disease Research and Diagnostic Lab.


The only way to prevent poisoning from blue-green algae is to remove the animals from the contaminated water. Harty encourages producers to move the livestock to a different pasture with a different water source, free of blue-green algae.

If this is not possible, she said it is necessary to control access to the pond, especially in areas downwind where the concentration occurs.

“Pump water from below the surface in the middle of the stock dam to a holding tank so that the scum on the top can be avoided,” she said.

The stock dam can be treated with copper sulfate as an algaecide, but consider the risk to fish and wildlife and ensure that the appropriate amount is added to the dam to control the algae bloom. Copper sulfate should be applied at 2 pounds per acre-foot of water, which is equal to 8 pounds per 1 million gallons.

If you suspect a blue-green algae bloom in your cattle drinking water, the first step is to move the livestock to a clean water source, then send samples of the water for analysis.

For more information, contact Harty at 605-394-1722 or or Robin Salverson at 605-374-4177 or