Blue-green algae blooms – caused by cyanobacteria whose toxins can affect the nervous system and liver, and which form in stagnant water under conditions of high heat and a high presence of nutrients – can be deadly to livestock and wildlife.
Most of us are familiar with algae blooms in our stock ponds. One of my ponds has gone through this process this year, with the water appearing thick and green with algae. It is, of course, related to heat and nutrients along with stagnant water that hasn’t been getting replenished.
While unpleasant and capable of depleting oxygen in the pond when decaying after the bloom, our standard run-of-the-mill algae blooms aren’t really a danger to our cattle. However, things are different with “blue-green algae.”
Also referred to as cyanobacteria, there are many species of blue-green algae that can poison animals. The two main types of toxins are neurotoxins, which affect the nervous system; and hepatotoxins, which affect the liver.
The clinical signs will depend on the type of toxin, with the neurotoxin form acting very fast, as in finding dead livestock right next to the pond. Meanwhile, the hepatotoxin will take longer to cause death, but death may still occur within a day or two depending on the dose. As always, sick or debilitated cattle in your pastures merit an immediate call to your vet.
Affected ponds will appear as if there is a bluish-greenish scum on the surface, although different species of cyanobacteria may also appear red or brown. This layer can be fairly thick, even to the point of resembling a thick paint. Although poisoning often occurs with this kind of dense bloom, cyanobacteria can be present at different locations in the water column, and signs in cattle or other animals around the pond should not be ignored just because the surface appears clear.
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The environmental factors that are responsible include warm weather and lots of nutrients, especially phosphorus and nitrogen. These are two components of manure, so ponds with runoff from pastures and areas with high manure concentrations, as well as fertilized fields, are likely to have the right nutrient composition.
In fact, blooms may follow storms that wash nitrogen and phosphorus into ponds, followed by periods of high temperatures. Wind may also increase the chance for toxicity by blowing the scum on the surface to one shore, and thereby concentrating the algae and the toxin.
While these blooms often occur in brackish water, they may also occur in fresher bodies of water. These toxins are very potent for wildlife, other livestock, and humans. One signal that something is wrong with a pond might be the discovery of dead wildlife in the vicinity of the pond, including dead frogs, raccoons or opossums along the shore. Fish can also be affected.
Even if not directly consumed, high concentrations of the toxins can be very irritating to human skin. Dogs are at a high risk because they may lick themselves to clean the algae from their coats if they went for a swim.
Algicides, such ascopper sulfate, may be effective in killing off a bloom, but be aware that killing off a large population will result in a sudden release of toxins from the dead algae. This actually makes the water more deadly for a period of time. Copper sulfate can also be harmful to marine life in the pond, so care must be taken to get advice on the correct dose and precautions.
Your veterinarian can help you find more resources on this potential threat to your herd, including getting in touch with a toxicologist to aid in evaluating blooms. I consulted several good resources in the form of Extension publications from the Iowa State University Beef Center, Kansas State University, and North Dakota State University, as well as the Merck Veterinary Manual. Your Extension agent will also likely have some resources to help you minimize your risk.