Animal Health Matters: Summertime brings threat of blue-green algae to animals

Russ Daly
Special to the Farm Forum

It’s been a long time coming, but we’re finally getting to the time of year when the water in our lakes is warm enough for summertime activities. Partly because of that phenomenon, our family is careful not to schedule its annual trip to “the lake” in northern Minnesota too early in the season. Some of those trips earlier in the summer have meant some pretty cold tubing or water skiing sessions!

Warming water temperatures are good for recreation, but also good for some of the life forms that call our ponds and lakes home. One of those is the group of organisms called cyanobacteria, or “blue green algae.” Under the right conditions, these organisms can multiply in ponds and stock dams that serve as water sources for animals on pasture. And for animals that drink that water, the consequences could be deadly.

Blue green algae appear green while in the water, but may take on a bluish tint as they dry on the shoreline. It’s very important to understand that most of the “pond scum” that normally forms on water sources in the summertime is not of the blue-green variety. Blue-green algae does not form a mat that you can pick up—the individual organisms are dispersed throughout the water. They often create the appearance of “green paint” on the water, a color best described as “John Deere green.”

Also, it’s only under certain environmental conditions that blue-green algae form. Hot, dry conditions – as well as high nutrient levels from runoff – favor the growth of these organisms, so blue green algae poisonings are typically a summer and early fall phenomenon. When these organisms “bloom,” they outstrip their oxygen supply, die off, and float towards the surface. Winds that push the algae to the shore then give animals easier access to the contaminated water.

Toxins produced by the algae are what causes death in cattle and other species—sheep, horses and dogs. These animals are at risk from drinking water containing these toxins. Additionally, dogs put themselves at risk when they swim in these waters and lick the algae off their coat. Some of these toxins affect the nervous system, resulting in muscle tremors and convulsions before death. Others cause liver damage, resulting in anemia, behavior changes and death. A quick onset is common: animals are usually simply found dead, often near the water source. Animals getting a lower dose become chronic poor-doers. Diagnosis of these poisonings in cattle involves having a veterinarian doing a post-mortem exam to rule out other causes of death, along with evidence of exposure to a source. Blue green algae can also affect people who swim in contaminated water – causing rashes and non-fatal illnesses.

How does one know whether the “scum” in your pond is blue-green algae, or something less harmful? First, consider whether the environmental conditions have been right for the bloom of algae, and whether the algae fits the description above.

If necessary, water samples can be tested by having your veterinarian send them to the lab. Diagnosis is made by directly looking at the algae under a microscope. The desired sample is a pint of fresh water collected where there is a high concentration of suspect algae is sufficient. Collect it in a clean container, keep it cool, and get it to the lab as soon as feasible.

Dealing with a stock dam that has a bloom of blue-green algae can be difficult, and usually is best accomplished by fencing livestock out of the area — at least the downwind areas where the algae may concentrate.

In some cases, water sources can be treated with copper sulfate to help diminish the problem.

While it’s still early yet, suspect blue-green algae poisonings have already been coming into the SDSU veterinary diagnostic lab, with confirmations pending. In most years we see positive samples at SDSU, along with reports of associated death losses. Keep an eye on your animals’ water sources as our summer progresses, and contact your veterinarian or Extension field specialist to investigate if you suspect problems. With a bit of vigilance, this potential problem can be identified and managed before animal illness or death occurs.