Blue-Green Algae Impacts on Cattle

Blue-Green Algae Impacts on Cattle

Cattle in pond
There are several ways to determine if blue-algae is present in the pond or dugout. Photo credit Troy Walz.

Hot, dry weather is impacting part of the state which in turn is impacting the water quality for grazing cattle.  In some pastures, the only water source available are ponds and dugouts which can contain hidden dangers to the cattle.

Blue-green algae also known as cyanobacteria blooms are caused by excess levels of nitrogen and phosphorus.  These nutrients are commonly introduced from runoff or soil erosion from fertilizer and manure.

The combinations of these excess nutrients with hot, sunny days can result in toxic algal blooms.  These blooms commonly occur in late summer and early autumn but can occur earlier depending on the weather.  When conditions are favorable, the bacteria can multiple rapidly with populations doubling in a day or less and persist for several weeks.  However, even with rapid bacteria growth the formation of toxic blooms is not predictable. 

Environmental factors such as rain, heavy winds or cooler temperatures will slow bacterial growth or break up the bloom.  Winds are very helpful in mixing the bacteria throughout the water body which reduces population growth.

Identification of Blue-green algae

Blue-green algae blooms occur commonly on stagnant ponds or dugouts where there is a potential of having high nutrient levels.  As the bacteria colony forms, it can appear as scum on or just below the water surface.  Actively growing cyanobacteria colonies can appear bluish, green, dark green or brownish green in coloration but can also be red or yellow in coloration.  The red or yellow colored colonies will turn a blue color after the colony has died and dried along the shoreline.


It is recommended to look for algae growth on the leeward (downward) side of the water body.  The winds will concentrate the bacteria, making it easier to identify.

Symptoms of Toxicity

There are several species of cyanobacteria found in the environment and not all species are harmful to animals.  However, the few that are harmful produce a toxin called cyanotoxins.  Cyanotoxins are harmful to nearly all livestock and wildlife including cattle, horses, sheep, chickens, ducks, songbirds, dogs, rabbits, frogs, fish and snakes.  These toxins are also harmful to humans.  The toxins affect primarily the nervous system and the liver.

Signs of cyanotoxin consumptions usually appears within 20 minutes of ingestion. Neurological symptoms include: weakness, staggering, difficulty breathing, paddling, convulsions, and death can occur 2-24 hours following ingestion. Hepatological (liver) symptoms include: weakness, pale-colored mucous membranes, mental derangement, bloody diarrhea and death.

Livestock that survive cyanotoxin poisoning typically lose weight but in some situations can develop photosensitivity.    Photosensitive livestock are prone to sunburns affecting the lighter colored areas of their body including the muzzle, udder, vulva/anus and areas with white hide.  Just like human sunburns, the affected areas will dry out, turn dark in coloration and peel exposing brand new skin.

Currently, there are no antidotes available for cyanotoxin poisoning.  Activated charcoal can be administered to decrease toxin absorption and atropine may serve to block acetylcholine receptors for the neurotoxin if suspected.  Thus, actively monitoring ponds and dugouts for blue-green algal blooms is critical and keeping cattle from drinking when bacterial populations become high. 

Copper sulfate (0.2-0.4 ppm) may be added to the pond or dugout to control blue-green algae growth.  Contact your local extension educator if you need assistance in determining the amount of copper sulfate to add.  Animals should not be allowed to drink from suspected ponds for a minimum of five days after water is treated because toxins will still be released as the algae cells die.

Is There a Problem? 

There are several ways to determine if blue-algae is present in the pond or dugout.  One way is by walking to the leeward (downwind) side of the pond or dugout to look for concentrated bodies of blue-green algae.  Also, the presence of dead mice, birds, snakes or fish are present, assume that poisonous conditions exist.

Necropsy any dead livestock by a veterinarian to rule out other causes of death.  If cyanotoxin poisoning is suspected, the veterinarian is able to collect appropriate samples for testing.

Collect water samples from the water body.  The water sample should be at least 500 milliliters in volume from the suspected area.  The sample should be taken from the surface of the water and deeper in the water.  While collecting the sample, be sure to wear gloves because cyanotoxins are also toxic to humans.  Once a sample is collected, place the sample in a cool place but do no freeze the sample.  In Nebraska, water samples can be sent to Midwest Laboratories, which according to The Nebraska Department of Environment and Energy is the only lab offering this service.

Prevention and Control

  • Apply and manage fertilizer and manure properly.
  • Implement a nutrient management plan and/or grazing management system that reduces levels of nutrients entering the water source.
  • Establish or maintain buffer strips of perennial plant species to reduce nutrients such as nitrogen and phosphorous from entering the water source.
  • Prevent livestock from loitering in surface water by installing alternate water sources and/or fencing to reduce access.
  • Create a designated drinking area where the risk of blue-green algae is minimal.  If wind concentrates the bacteria on one corner of the water body, fence that corner off.  Force cattle to drink from the windward side of the pond or dugout, where bacteria cannot concentrate.
  • Pump water from the center of the water body well below the surface to a water tank.  Bacteria concentrations are typically higher on the water surface.
  • Construct drinking ponds so they are 20 feet wide by 80 feet long and 10 feet (water depth) deep.  This decreases the surface area needed for multiplication of the blue-green algae, maintains an adequate supply of water for the livestock and decreases the effect of wind on the surface of the water body.

Lutz, S.  2003.  Bovine Blue-Green Algae Toxicosis.  Purdue University Fall 2003 Newsletter. (

Meehan, M.A. and Mostrom, M.  2021.  Cyanobacteria (Blue-green Algae) Poisoning.  North Dakota State University Extension Publication V1136. (

Purchner, B., Galey, F., Johnson, B. et al.  1998.  Blue-green algae toxicosis in cattle.  JAVMA 213:1605-1607.


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