I had an interesting case discussion with a Saskatchewan veterinarian last week.
He was investigating a case of sudden death in a cow-calf herd. One cow and one calf had died very suddenly out of a group of 80 pairs on native grass.
Both the cow and calf were found dead right next to the dugout. The local veterinarian was suspicious of blue-green algae toxicity, but we discussed several other causes of sudden death, including sulfate toxicity, nitrates, lead toxicity and anthrax.
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Another cow-calf pair looked to be weak and wobbly, but they both improved without any treatment.
The producer wisely fenced off the dugout immediately so that the cows no longer had access to that water source.
The veterinarian had the producer submit a water sample to the veterinary diagnostic laboratory, and the results came back as positive for one of the two common toxins that are related to blue-green algae toxicity.
This toxic condition is actually caused by a bacteria known as cyanobacteria, which was previously known as blue-green algae.
The growth of these toxigenic cyanobacteria has also been termed freshwater harmful algal blooms (FHAB) and tends to occur when water temperatures are above 20 C and in relatively stagnant water sources.
Nutrient rich water will support the growth of cyanobacteria, and so dugouts or other water sources that have runoff or soil erosion that allow fertilizer or manure to enter the water are more likely to have blue-green cyanobacteria growth.
When conditions are favourable, the bacteria can grow rapidly, doubling their numbers in one day or less.
The toxic blooms are very unpredictable and often do not last long. Cooler temperatures or heavy winds can inhibit growth or break up the blooms.
Blue-green algae blooms can appear as scum near the surface of the water. The water can be green, bluish or brownish green in appearance and sometimes even red or yellow.
Once the cyanobacteria die, they may turn blue along the shoreline. It is also possible that the wind can concentrate the bacteria on one side of a water body, making it more toxic for the animals that drink on that side.
The toxins produced by cyanobacteria are harmful to all animals and can affect cattle, horses, sheep and wildlife. They have almost immediate effects, and symptoms can occur within 20 minutes of ingestion of contaminated water.
They can affect the nervous system and damage the liver. Symptoms might include weakness, staggering, muscle tremors, convulsions and difficulty breathing.
If the cattle consume the toxin that causes liver damage, you might see longer-term effects, such as photosensitivity, or they may eventually die of liver damage.
The water from this dugout tested positive for Anatoxin A, which is one of the most rapid acting cyanotoxins. It is rapidly absorbed and clinical signs are almost immediate.
The cow and calf probably died very quickly from respiratory paralysis.
Unfortunately, there are also no obvious post-mortem lesions for veterinarians to diagnose in these types of deaths.
It’s important to differentiate blue-green algae blooms (cyanobacteria) from other things such as duck weed or other filamentous algae.
If you’re not sure about the water source, you can take a picture and send it to a local livestock extension specialist or you can take an approximately 100 millilitre sample of water and send it to the veterinary diagnostic laboratory for analysis. It’s probably best to freeze the water sample before submitting it to the lab.
Water contaminated with cyanobacteria can be treated with copper sulfate. You want to be careful and use only the recommended amounts for treating dugouts because too much can be harmful to other beneficial organisms in the water.
It is usually recommended to not allow livestock to contact the water for approximately two weeks following treatment to allow all the toxins to dissipate.
Water quality is an important issue when the temperatures start to rise. In this case, it was blue-green algae, but we have seen similar sudden death scenarios with high sulfate water sources causing polioencephalomalacia.
It’s important to monitor your water sources and work closely with your veterinarian to diagnose the cause of any sudden death cases.
