Perennial ryegrass staggers and phalaris staggers
Elle Moyle, Hamilton District Veterinary Officer, Agriculture Victoria
Perennial ryegrass staggers
The current extraordinary season of rainfall and pasture growth leading into late summer and autumn may be setting us up for a diabolical perennial ryegrass staggers (PRGS) year in many areas of the state.
PRGS is seen when sheep graze tall, dry ryegrass (Lolium perenne) particularly in late summer and autumn, and often following sufficient rain to stimulate limited pasture growth. We have previously seen similar years in 1986 and 2002, when PRGS was prominent.
PRGS is usually observed as temporary incoordination (hence the name ‘staggers’) in sheep and cattle. This occurs when endophytes (fungus) are established in older stands of perennial ryegrass pastures. The endophytes produce a toxin that protects the plant from insects and helps with establishment, but also interferes with the nervous system of sheep.
Sheep, cattle and horses are all susceptible; however, PRGS is usually seen more in younger animals. Weaners should be closely monitored during this time.
PRGS develops within 7–14 days of the ingestion of toxic pasture.
First signs are usually fine tremors of the head. More severe signs are seen with exercise or under stress, such as mustering. These include stiff movements and incoordination, often resulting in collapse with stiffly extended limbs. The ingested toxin can also induce high body temperatures, so sheep may try to cool themselves in dams and troughs, sometimes drowning or otherwise injuring themselves in the process.
There is no specific treatment for PRGS. It is best to remove an affected flock from the source of the problem by moving them quietly (without a dog) into another paddock. It is important to avoid stressing affected stock, as this will worsen their condition. Animals will recover once removed from the pasture for one to two weeks. Cases will cease following a significant break in the season and onset of cooler weather.
If exposure to toxin is prolonged, permanent neurological damage can occur.
PRGS could be a significant issue this season as a result of the rainfall seen across parts of Victoria in the past six months, which has led to significant pasture growth and standing feed bank going into summer. It is recommended that you act early to graze off your ryegrass to prevent having tall, dry ryegrass in late summer.
Perennial ryegrass staggers (PRGS)
- Great season means an increased risk of PRGS.
- Highest risk in March–April with high carryover of dry ryegrass.
- Graze ryegrass paddocks in early summer to reduce risk.
- Inspect mobs twice weekly from mid-January for signs.
If you see signs, immediately and quietly remove flock from paddock (very slowly, with no dogs).
Phalaris staggers (PS) is a common syndrome that is associated with the intake of green, actively growing phalaris at a time when it contains toxic alkaloids.
The risk of PS is associated with soil cobalt levels (marginal or deficient in cobalt), animals’ access to ingestion of soil and the amount of phalaris in a pasture.
Typically, PS is of low risk in summer however it may occur at any time of the year, especially late autumn/winter. If you have had significant summer rainfall that has either led to early growth of phalaris or the rain has flattened tall grass that may reduce the level of soil ingestion (and thus dietary cobalt), then you may experience PS in your flock earlier than usual.
Clinical signs of PS may occur after 14 days of grazing green, actively growing phalaris and can occur up to five months after sheep are taken off phalaris pasture. The clinical signs include head nodding and bunny hopping with a wide hindleg-based gait. These signs are often noticed when mustering or handling.
Mildly affected animals may recover; the chance of recovery is higher the more rapid the onset of signs. If the symptoms are more severe, there is no specific treatment, and the animal should be euthanised.
PS can be prevented by cobalt supplementation: two intraruminal cobalt bullets (will prevent PS for three years) or cobalt foliar sprays (annually soon after the autumn break) are the most effective ways to prevent PS in high-risk areas.
Phalaris staggers (PS)
- Associated with grazing green phalaris for at least 14 days, combined with low cobalt intake
- Ingested soil is a major source of dietary cobalt
- La Niña increases summer risk of PS, particularly if rain events cause enough matting of dry feed to prevent soil ingestion
- Prevent with cobalt bullets every three years or annual pasture spray