Editor’s note: This was written by Wilson K. Rumbeiha, Diagnostic Center for Population and Animal Health and appeared in the April 2010 Michigan Dairy Review.
Blue green algae, also known as cyanobacteria, are microorganisms with characteristics that fall between those of bacteria and plants. They grow in water bodies in tropical, subtropical and temperate regions all around the world. In Michigan, blooms of blue green algae occur any time from late spring to early fall (June through September or October) but more especially in July and August.
For blooming to occur, the right combination of environmental conditions must exist and these include warm sunny weather with temperatures ranging from 50 to 86 degrees Fahrenheit, phosphorus concentrations in excess of 30 micrograms/liter, and high water nitrogen content. Some of these environmental conditions are consistent with water pollution, generally referred to as eutrophication.
Around the world blue green algal blooms are found both in fresh and brackish water bodies. In Michigan, blue green algal blooms are associated mainly with fresh water bodies. For the past 3 years there have been more than usual inquiries or reports of blue green algal poisoning in cattle in Michigan. In summer of 2008 there was an unconfirmed case on a dairy farm in Michigan in which nine out of 80 cows died suddenly.
Toxic Species and Compounds
There are hundreds of blue green algal species but only a handful are associated with poisoning in animals. Common poisonous species include Microcystins, Anabaena, Planktothrix, Nostoc, Oscillatoria, and Anabaenopsis. These species of blue green algae produce different kinds of toxins of which two classes -- microcystins and anatoxins -- are responsible for most animal deaths. Microcystins poison the liver, whereas anatoxins target the nervous system.
The majority of blue green algal poisoning is caused by microcystins. Naturally, these toxins are found inside algal cells, but stressful conditions such as treatment of water with algaecides or natural death of cells results in release of these potent toxins.
Cattle can be affected by drinking water containing toxins or intact blue green algal cells. In small lakes or large ponds of water, wind effect tends to concentrate the blooms on one side of the water body. Cattle are usually poisoned when they drink from the windward side of these stagnant water bodies where the blue green algae have accumulated.