Both water availability and quality are important considerations for cattle at grass, particularly during periods of hot weather. Although rare, cases of blue-green algae (or cyanobacteria) toxicity have been occasionally diagnosed in cattle by SRUC Veterinary Services and sheep can also be affected. This condition should be considered in cases of otherwise undiagnosed sudden death, particularly in cattle at grass depending on their water supply.
In the acute stages of the disease where the onset is rapid, cattle can show nervous signs and muscle tremors. In the chronic form of the disease, cattle will have liver damage caused by the ingested toxins. Liver damage can make cattle more susceptible to photosensitisation, which is inflammation of the skin and sometimes the eye due to exposure to sunlight. Algal toxicity is more commonly diagnosed by changes in liver tissue observed in postmortems and so outward signs of a problem are not always detected before it is too late.
High water temperature, shallow water and high concentrations of nitrogen in the water pre-dispose to algal blooms. Excess phosphorus from fertiliser application and manure from over-supplementation of livestock can also contribute to algal blooms if phosphorus makes its way into water courses. Animals drinking near the edge of a pond are more at risk as the algae and toxins are concentrated close to the water’s surface. Another risk factor might be water troughs in fields that have been shut up for silage that then return to grazing where water troughs might need cleaning and water refreshed.
Depending on how the rest of the summer’s weather goes the risks of this condition occurring might be higher. It is a good prompt for farmers to ensure that water troughs are cleaned out. There are regulations on how and where livestock should have access to water courses from an environmental perspective and if there are concerns about algal blooms, livestock should be fenced off from affected natural water supplies.
Lorna MacPherson, email@example.com
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