Perennial ryegrass toxicosis = potential summer risk
5 January 2017
Most old or naturalised perennial ryegrass pastures contain fungal endophytes which can produce high levels of alkaloids that can be toxic to livestock.
Agriculture Victoria Senior Veterinary Officer Robert Suter said the symptoms are collectively called perennial ryegrass toxicosis (PRGT) and cover a range of nervous disorders including staggers, ill thrift, heat stress, scours and possibly lower fertility.
Serious outbreaks occur in high rainfall areas across Victoria when big springs are followed by a hot and dry autumn.
Mr 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. The key indicators of high risk to animals (this includes sheep, cattle and alpaca) were identified as:
- A dominance of perennial ryegrass in the pasture (with Wild Type endophyte).
- A big spring with high rainfall in spring-summer that prolonged the length of the growing season.
- This was followed by dry conditions in March and high average maximum temperatures in March (230C) and April (20oC).
While the forecast for autumn is not currently predicting hotter and/or drier conditions than usual, much of Victoria has experienced abundant spring growth. If you have experienced severe issues in the past, it is worth considering now what you might do to reduce the impacts this time.
These would include:
- Assess each paddock on the farm for the risk of PRGT (knowledge of past effects).
- Identify which paddocks shouldn't be grazed by susceptible classes of stock (young sheep or cattle or breeding ewes) in the high risk period. If this is a high proportion of paddocks then consider using stock containment areas for joining ewes if spring lambing, and weaners.
- Limit time stock spend grazing high risk paddocks, and minimise seed head production and access to seed heads.
- Ensure access to plentiful water with a low risk of drowning.
Supplementary feeding on high risk pastures is unlikely to reduce the risk, and may worsen the staggering seen.
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 but still have persistence attributes for the plant.
The information in this article has been sourced largely from 'Management of perennial ryegrass toxicosis' authored by Kevin Reed and John Webb Ware and published by MLA.
Categorised under: Agriculture