Senior veterinary officer Robert Suter said most old or naturalised perennial ryegrass pastures contained fungal endophytes, which could produce high levels of alkaloids that could be toxic to livestock.
He said PRGT covered a range of nervous disorders including staggers, ill thrift, heat stress, scours and possibly lower fertility. Serious outbreaks occured in high rainfall areas across Victoria, when big springs were followed by a hot and dry autumn.
Dr Suter said in 2002 it was estimated that 90,000 sheep and 500 cattle died from direct causes of these alkaloids and a similar number from indirect causes.
While the forecast for autumn is not currently predicting hotter and/or drier conditions than usual, much of Victoria has experienced abundant spring growth.
The key indicators of high risk to animals, including sheep, cattle and alpacas, were a dominance of perennial ryegrass, high rainfall in spring and summer, which prolonged trhe length of the growing season, and dry conditions and higher average temperatures in March and April. “While the forecast for autumn is not currently predicting hotter and/or drier conditions than usual, much of Victoria has experienced abundant spring growth,” Dr Suter said. “If you have experienced severe issues in the past, it is worth considering now what you might do to reduce the impacts this time.”
Dr Suter said this could include paddock assessment for PRGT, based on knowledge of past events, identifying grass, which should not be grazed by young sheep or cattle and breeding ewes.
“If this is a high proportion of paddocks, then consider using stock containment areas for joining ewes, if spring lambing, and weaners.”
It would also be advisable to limit the time stock spent grazing high risk paddocks and minimise seed head production and access to seed heads. Supplementary feeding on high risk pastures was unlikely to reduce the risk and might worsen staggering. “For the long-term, consider resowing pastures with other pasture species (e.g. phalaris or fescue) or other ryegrass cultivars that have animal ‘safe’ endophytes.”