Algal poisoning of livestock is a real threat this year due to lower than normal dam levels. There have been several outbreaks of blue green algae in dams on properties throughout Western Victoria with one sample confirmed to be Anacystis spp. algae.
Algal blooms occur when the combination of nutrients (phosphorus and Nitrogen) light and temperature are optimal for development. The algae rise and fall through the water column, coming to the surface to photosynthesize, and then sinking again until their carbohydrate reserves are depleted. The algae are spread from dam to dam by carriers (i.e ducks), and the spores of the algae can live in the mud on the bottom of a dam for many years, so unfortunately, if you experience an algae problem on a dam, you will experience it again down the track.
When the algae begin to die (turning a scummy/blue colour), they release toxins that are harmful to livestock. Some of these toxins produced are as lethal as the toxins produced by a blue ring octopus or a brown/tiger snake and primarily cause blood poisoning to livestock usually within 24hrs of drinking the water. Both liver and kidney damage occur, and for animals that do not die immediately, may develop jaundice or severe photosensitisation. There is NO TREATMENT for affected livestock. Stock affected by algal poisoning show nervous tremors and a staggery gait. They quickly become recumbent, begin to convulse and die. Usually the animals’ mouth, nose and feet will be stained green by the algae, and a post mortem by a veterinarian will confirm the cause of death.
The most practical way to reduce the risk is to remove stock from paddocks with affected dams. This involves monitoring the water source and waiting for 2-3 weeks after the scummy blue phase has passed. Re-testing the water at this point will give you piece of mind before putting stock back into the paddock. Testing water for toxin levels is hugely expensive (thousands of dollars) but be mindful that some toxins can survive for a period of time after the algae have disappeared.
There are commercial algicides that can be used such as Coptrol but these products yield variable results, usually only killing the surface algae, not the algae below the surface. The use of products containing Copper Sulphate can also increase the risk of livestock deaths, particularly if livestock have already suffered liver damage caused by the algal toxins. Products such as “Phoslock” permanently locks up the phosphate and makes it inaccessible to the algae. Aerating the affected dam with a fire pump is unlikely to be of any benefit. The algal bloom will usually disappear with time so patience is paramount. To discuss treatment options, call Steve at Dynamic Ag.