Stagnant pond water consumed during hot, dry weather can be dangerous to livestock, reminds Charles Stoltenow, North Dakota State University Extension veterinarian. "The water can contain certain species of cyanobacteria (formerly known as blue-green algae) that typically grows in stagnant, warm pond water." At least four types of potentially poisonous cyanobacteria are known to occur. Toxins from these bacteria are poisonous to most livestock, including cattle, horses, sheep, pigs, chickens, domestic and wild ducks, pigeons, geese, and even frogs, fish, and snakes.

The toxins primarily affect the nervous system and the liver. Signs of cyanobacterial poisoning include nervous derangement, staggering, tremors, and severe abdominal pain. The toxins are also poisonous to humans. Take note of any dead wildlife around bodies of water, Stoltenow advises. A close watch for unexplained livestock deaths is also important. Consult a veterinarian to find a cause of death so steps can be taken to prevent additional livestock deaths. There are no known antidotes for cyanobacteria poisoning.

The algae flourish only in the top few inches of water, so toxic concentrations are typically found only in small ponds where waves don't mix the water thoroughly. Cyanobacteria blooms don't occur in lakes and rivers. Under favorable conditions, the algae can double in number in 24 hours and can turn pond water blue to brownish green. If a pond contains toxic concentrations, keep animals from drinking from it by fencing off the water and providing another source of water. Because the toxins are concentrated at the surface, water may be pumped from the bottom of deep sloughs or potholes to watering tanks.

Typically, toxic algae blooms last only a few days but may persist for several weeks. A veterinarian can help determine if a pond has toxic concentrations of the algae. More information on cyanobacteria and protecting livestock is available at www.ext.nodak.edu/extpubs/ansci/beef/v1136w.htm.
-- Clint Peck