Annual ryegrass toxicity (ARGT) is a potentially fatal poisoning of livestock after consuming annual ryegrass infected by the bacterium Rathayibacter toxicus (formerly known as Clavibacter toxicus).
All grazing animals are susceptible to ARGT, including sheep, cattle, horses and pigs.
How ARGT develops
The cycle starts with a migratory nematode called Anguina funesta. These nematodes can travel into the flowering parts of developing Wimmera ryegrass (Lolium rigidum) and colonise them, eventually taking over the seed head to form nematode galls.
Problems concerning ARGT begin when the bacterium R. toxicus is present in soil and carried by the nematode as it moves into the developing ryegrass flowers. The bacterium often out-competes the nematode to take over the seed heads. The bacterium produces toxins from the end of flowering, through seed set, to seed maturity.
Dried out infected ryegrass remains toxic. Hay made from toxic ryegrass will also be toxic.
The toxins that cause ARGT (corynetoxins) are cumulative meaning the more the animal consumes, the greater the impact. It takes up to 6 months to clear all effects of the toxin. If the animal consumes toxins up to 9 weeks apart, those toxins will accumulate until they cause clinical disease.
Signs of ARGT in livestock
ARGT causes neurological signs brought on by stress or activity. The disease is often first suspected when animals are being moved for yarding or to change paddocks. If the animal is left undisturbed it may appear to recover, regain its feet and rejoin the mob with a stiff gait.
Animals may be found dead with evidence of convulsions before death. Intermittent appearance of clinical signs is a feature of this disease.
Before being moved to the new paddock, the previous paddock where the stock were located should also be checked for ARGT.
In cattle and sheep, ARGT may cause the following signs:
- neurological signs exacerbated by stress or movement
- uncoordinated movements
- falling over and if they recover and regain feet, will re-join mob with stiff “rocking horse” gait
- convulsions in fallen stock with strong muscular movements, often with the head thrown back and stiff limbs
- pregnant stock may abort
- death.
Signs of ARGT may appear as soon as 4 days or as late as several weeks after animals are introduced to toxic feed (pasture, hay, grain). If clinical signs appear sooner than 4 days after stock are introduced to a paddock, stock have already ingested the toxin in the previous paddock.
Diagnosing and treating ARGT
A history of neurological signs, first appearing when animals are being driven, is strongly suggestive of ARGT.
There are a range of laboratory tests to assist with diagnosis of ARGT. Faeces and rumen contents can be tested for the presence of the toxigenic bacterium. Tests can also be conducted for the prevalence of the bacterium in pasture, hay, silage, processed feed and grain samples. Histopathology can be used to identify key changes in brain and liver that can also indicate ARGT.
There is no specific treatment for ARGT,. With time, less severely affected animals may recover. When affected animals are found:
- Immediately and calmly move the stock to a ‘safe’ paddock with clean water, safe feed and shade.
- Badly affected stock should be protected from weather and predation.
- Stock unable to rise within 12 hours should be humanely euthanised.
Animals may continue to show clinical signs for up to 10 days after being moved from the toxic paddock. Peak deaths in ruminants occur 4 days after removal from affected feed source. Not all animals that develop clinical signs will die.
A safe paddock is one which has been tested and reported as “Not detected - no risk (on average less than 1 gall/kg in sample supplied)” for ARGT during the current season.
Animals in paddocks or being fed feed that tested as a "very low risk" or “low risk” should be observed daily for signs of ARGT and removed to a safe feed source as soon as signs appear. Animals should not be grazed on or fed “high risk” pastures or feed.
Refer to Testing for ARGT risk below for more information.
Horses are susceptible to ARGT though signs may differ slightly from those seen in livestock. Affected horses may stop eating, show muscle tremors, and become increasingly reactive to stimuli. Neurological signs can escalate quickly, including lack of coordination, disorientation, and seizures.
Since there is no specific treatment for ARGT, the priority is to remove the horse from the contaminated feed source immediately. Provide fresh hay and clean water, keep the horse in a calm, quiet environment. If you suspect your horse may have ARGT, contact your private veterinarian as soon as possible for further care and monitoring.
How ARGT may be prevented
The keys to preventing ARGT occurring in livestock are:
- daily inspection and immediate removal of stock to a safe feed area if they show signs of ARGT
- good biosecurity to minimise the introduction of the ARGT-causing organisms through contaminated feed such as hay
- paddock management to prevent seed
- vendor declarations for bought-in hay, grain and that show the testing status for ARGT
- testing hay, silage, processed feed, grain and pasture for ARGT.
Between October and December, stock grazing paddocks which contain annual ryegrass should be inspected at least once daily to monitor for early signs of ARGT.
When stock are placed onto stubbles containing ryegrass in summer, they should be inspected daily for the first 2 weeks.
Inspection should involve moving the mob briskly over 100 to 200 metres as the signs of ARGT are brought on by stress or activity. Early detection of the disease will allow action to be taken to minimise losses.
Any means of spreading ryegrass seed can spread the organisms that cause ARGT.
These include movement of contaminated feed (hay, grain), infected ryegrass seed, machinery or vehicles that have not been cleaned, or animals carrying galls in their fleece. The galls weigh less than the seed and can be moved by strong winds. Surface run-off, water and creeks can move the organism considerable distances.
Once the organisms are introduced, paddock management is an important way of reducing the risk of ARGT.This should include regular cropping or cutting of hay or early pasture topping within 10 days of the start of flowering.
When buying hay, it is recommended that you ask for a vendor declaration before purchase and to view the ARGT test results.
Hay vendors are encouraged to show prospective buyers the DPIRD Diagnostics and Laboratory Services (DDLS) test results with the risk rating on their samples. Suitable vendor declarations and more information are available from Integrity Systems.
Testing for ARGT risk
Ryegrass testing in paddocks can identify safe paddocks and detect bacteria early so it can be managed. For the most accurate results from testing, carry out sampling according to the instructions below.
Samples should be:
- 1 kg or roughly a “pillowcase” sized sample
- clearly labelled to identify the area it was taken from
- tightly sealed to prevent loss of the sample or potential cross-contamination.
The label appearing on the sample(s) is what will appear on the final report.
If there are multiple bales of hay, collect a sub-sample from up to 10 bales to make up a total of 1 kg. For example, if there are 10 bales, collect approximately 100 g hay from each bale to make up 1 kg.
Hay bale sampling
Take representative ‘grab’ samples from within the bale. Only ryegrass seeds contain the toxin, however to assess the risk of feeding the hay, include a similar percentage of ryegrass in the sample as is present in the hay.
Sample as close as possible to the centre of the bale, as this area is most likely to be compressed and will hold all ryegrass seed head (if present) in place.
Paddock sampling
Collect a small handful of pasture from approximately 100 well-spread points across the paddock. Walk the paddock for a thorough check or use a vehicle for speed, but ensure all areas – especially spots like headlands, fence lines, dams and tree belts – are covered.
Don’t mix samples from different paddocks. For large paddocks, sample sections separately, but a single, well-collected sample can still provide valuable information.
Testing takes a minimum of 24 hours, as pastures need to be soaked overnight prior to testing. During peak season, allow up to one week after receipt by DDLS.
To send your ARGT sample to DDLS:
1. Put the hay sample/s into a clean plastic bag that can be well-sealed to prevent loss of sample and potential cross-contamination of samples.
2. Label the sample with your name and property identification code (PIC). If multiple samples are submitted, label with an identifier such as 'Bales 1 to 10' so you can identify from which area in the paddock samples were collected.
3. Complete a laboratory submission form to accompany the samples. Ensure the PIC box is completed on the submission form.
4. For clients submitting their own pastures, use the Annual ryegrass toxicity (ARGT) testing submission form.
- For clients submitting via a veterinarian or other consultant, use the DDLS Animal Pathology Diagnostic Submission Form.
- Deliver the samples by post or courier:
By post: Send the bagged hay sample in a suitable container (satchel bag, cardboard box, dry foam esky) to DDLS:
DDLS – Specimen Reception, Building 102
Department of Primary Industries and Regional Development
3 Baron-Hay Court
SOUTH PERTH WA 6151
Email: DDLS@dpird.wa.gov.au
In person: follow the signage to DPIRD main reception between 8:30 am and 4:30 pm:
3 Baron-Hay Court
SOUTH PERTH
Note that access to the rest of the South Perth site is restricted.
The cost of conducting testing for a 1 kg hay sample (from up to 10 hay bales) for ARGT risk is:
- $52.88 (incl. GST) per sample
- $31.57 (incl. GST) handling fee per submission.
If the sample was sent from a regional DPIRD office, courier fees may also apply.
Note: prices are subject to change at the end of a financial year so please visit DPIRD’s Fees and Charges page for the current financial year price booklet.
Contact: DDLS South Perth
Phone: +61 08 9368 3351
Email: ddls@dpird.wa.gov.au
Look and report
If you see unusual disease signs in your stock, call your private vet, a DPIRD Field Vet, or the Emergency Animal Disease hotline on 1800 675 888.
Livestock with neurological signs which meet certain criteria may be eligible for the or the Significant Disease Investigation (SDI) program. The cost of the veterinary investigation will be subsidised in eligible cases.
Related information
- Annual ryegrass toxicity testing submission form (154 KB)pdf
- Significant Disease Investigation (SDI) program
- A guide to diagnostic sampling in ruminants - annual ryegrass toxicity and toxic algae (86 KB)pdf
- National Transmissible Spongiform Encephalopathy Surveillance Program (NTSESP) Scrapie
- Hendra virus