Hot, dry weather that affects parts of the state each summer and fall can affect the water quality for grazing cattle. In some pastures, the only water sources available are ponds and dugouts that 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 they can occur earlier depending on the weather.
When conditions are favorable, the bacteria can multiply rapidly with populations doubling in a day or less and persisting 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 helpful in mixing the bacteria throughout the bodies of water, 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, but they also can be red or yellow. 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 body of water. 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 also are harmful to humans. The toxins affect primarily the nervous system and the liver.
Signs of cyanotoxin consumption usually appear within 20 minutes of ingestion. Neurological symptoms include weakness, staggering, difficulty breathing, paddling and convulsions, and death can occur two to 24 hours after 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 or anus, and areas with white hide. Just like human sunburns, the affected areas will dry out, turn dark in color 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, along with keeping cattle from drinking when bacterial populations become high.
Copper sulfate (0.2-0.4 parts per million) 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-green 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, if dead mice, birds, snakes or fish are present, assume that poisonous conditions exist.
Necropsy any dead livestock 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 body of water. 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 also are toxic to humans. Once a sample is collected, place the sample in a cool place, but do not 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
Follow these tips to prevent the formation of toxic algal blooms:
- Apply and manage fertilizer and manure properly.
- Implement a nutrient management plan 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 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 body of water, 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 body of water 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 body of water.
Timmerman is a Nebraska Extension educator.