Blue-Green Algae

Posted by Nancy S. Loving, DVM on 06/08/2020

You’ve probably read the recent reports about dogs dying soon after swimming in waterways contaminated with blue-green algae. Nothing could be more horrifying than seeing your beloved, happy dog come out from the water, and shortly thereafter become fatally sick. This situation is not unique to dogs playing in algae-infested water. Horses, livestock, and people are all subject to the same toxicity.

Let’s start at the beginning. How do waterways become infected with blue-green algae, otherwise known as cyanobacteria? The most common condition that promotes rapid algae growth is the influx of specific nutrients, such as those found in fertilizer, sewage and animal waste, and decaying organic debris: Phosphorus and nitrogen. Add to this recipe water that is slow moving or calm and shallow with warm temperatures, especially over 64 degrees Fahrenheit. The most common seasonal time to see toxicity is in summer and early fall when conditions are hot enough to favor algae growth. In warmer climates, the danger lurks as soon as springtime temperatures rise above 64 degrees Fahrenheit. Before long, algae blooms form a green scum on the water’s surface. When checking water for algae, one misleading situation is that rain, wind, or currents may force the algal bloom beneath the surface for a short time, only to reappear when the water calms.

Keep in mind that it doesn’t take a large water source to threaten horse health with algae blooms. Cyanobacteria can grow in even the smallest water containers – horse watering troughs or automatic waterers, birdbaths, and even something as small as a garden pot, for example. Routine and regular cleaning of all horse watering devices is important to limit this risk, especially in the warm months of the year. 

How is it Toxic?

Of more than 2,000 species of blue-green algae, at least 80 produce toxins that are poisonous to humans and animals. Blue-green algae produces two types of toxins – microsystins and anatoxins – that affect many systems: Microsystins cause liver damage; anatoxins affect the neurologic system. 

Contact with affected water, either by drinking algae-laced water or by licking contaminated wet skin, causes poisoning. Consumption of dried algal mats is similarly dangerous. Toxins are released from algal cells that are damaged or digested, or when the algae die. Even after algal blooms have disappeared from view, the water can still be toxic, and there are reports that dried algal scum is toxic for as long as five months. 

The only way to confirm if a water source is infected with cyanobacteria is to test it in the lab. Not all infected water is tinted blue-green; and not all blue-green discolored water harbors cyanobacteria. Winter is not the total answer to removal of this hazard from water: Cyanobacteria are able to survive beneath ice and in winter conditions. 

Signs of Toxicity

Signs that a horse is affected are variable, ranging from liver disease – jaundice, unthriftiness, and skin photosensitization (sunburn) – to neurologic signs of disorientation, muscle tremors or rigidity, staggers, collapse, seizures or convulsions. Horses may also experience respiratory distress, excessive salivation and tearing, pale mucous membranes, colic and diarrhea or bloody manure. 

Toxicity affects horses fairly rapidly, leading to death within 24 hours of exposure, and sometimes within 20 minutes to hours depending on the amount of water consumed. Wind blowing across water is able to concentrate cyanobacteria in specific areas downwind. Just one quart of contaminated water is enough to kill a cow.

How You Can Prevent Toxicity

An ounce of prevention is worth a pound of cure, the saying goes. Illness or death from cyanobacteria is a terrible thing for an animal to experience, so you can have a huge impact on preventing such sickness or fatalities. If you have ponds or slow-moving water on your property, fence the horses away from these water sources. Provide a fresh water source that is routinely cleaned, and that isn’t contaminated with manure or urine. And, don’t forget that this same caveat goes when you are on the road with your horses – don’t be tempted to let them drink from unknown murky or scum-laden water during rest stops, trail rides, or at events.

If you fertilize your pastures and fields, make sure the fertilizer doesn’t run into the waterways. Similarly, discard and compost your manure on flat areas at a far distance from water sources with no chance of drainage into waterways.

Treatment of a water source with an algae-killing compound, like copper sulfate, should be followed by complete restriction of horses drinking that water for at least a week. Even longer is better. This gives time for toxins released into the treated water to degrade sufficiently.

What About Blue-Green Algae Oral Supplements?

Horse owners often want to find the magic elixir that makes their horse stronger, faster, more robust with a competitive edge. One such supplement fed to horses contains blue-green algae, referred to as pond scum but marketed as a “superfood.” With limited knowledge, a horse owner might be tempted to feed this. However, supplements are not necessarily benign and can, in fact, prove fatal. Manufacturers of this product harvest it during algal blooms to produce a popular supplement fed to horses. 

A journal paper (Mittelman, NS et al, Presumptive Iatrogenic Microcystin-Associated Liver Failure and Encephalopathy in a Holsteiner Gelding, Journal of Veterinary Internal Medication, 2016; 30: 1747-1751) describes a case of an 8-year-old Holsteiner gelding that received the powdered blue-green algae supplement for two months for “purported hoof health benefits.” Three days before the horse became ill, a new container was used. He developed jaundice, had a poor appetite and a dull mental state, began yawning compulsively, and showed mild signs of colic. Blood chemistry parameters indicative of liver disease were elevated. 

The horse was treated for liver failure with medications important for decreasing brain edema and high ammonia levels, along with supplementation using intravenous fluids and dextrose. Despite treatment, the horse developed mania – involuntary biting and compulsive circling – and was euthanized two days after admittance. Necropsy results identified a small, flaccid (like a dishrag) liver, which on histology was consistent with microcystin toxicity that causes hepatic failure and hepatoencephalopathy (neurologic signs subsequent to liver toxicity). Of five unopened containers of the supplement tested, three contained microcystin, a component of blue-green algae. 

It is important to keep in mind that nutraceuticals (nutritional supplements) are not scrutinized by the Food and Drug Administration (FDA) as closely as pharmaceutical medications, and in many cases, not at all. This then falls into the laps of horse owners to be discriminating about their purchases. “Buyer beware” is a difficult position to be in when it comes to doing right by your horse and not just blindly following the latest trend.

If you search online, you will see many holistic practitioners recommending blue-green algae, including spirulina, as a supplement for horses. Despite lack of evidence-based documentation, these reports claim that blue-green algae have benefits for hooves and joints. There are far better and safer supplements – both oral and systemic (via intramuscular or intravenous) administration – to address these and many other musculoskeletal issues. Consult with your veterinarian about some options that provide good efficacy for managing musculoskeletal concerns yet have minimal and preferably no adverse effects.

Subscribe to receive news and updates.