FEBRUARY 2007 PRIMEFACT 429 (REPLACES AGFACT A0.9.4)

Annual ryegrass toxicity and blown grass/beard grass poisoning

Dr Chris Bourke grasses such as blown grass and annual beard grass can also be infected. Annual ryegrass toxicity Principal Research Scientist (Poisonous ), is widespread in the agricultural districts of SA and Orange Agricultural Institute the wheat belt of WA.

This Primefact covers annual ryegrass toxicity Annual beard grass toxicity is a persistent problem (ARGT) and the related livestock poisonings in some areas of south-eastern South and associated with blown grass ( avenacea) blown grass toxicity occurs intermittently in north- and annual beard grass (Polypogon monspiliensis), western NSW. in NSW Australia. Rathayibacter toxicus infection has so far not been For at least 40 years an unusual form of poisoning detected in annual ryegrass infested pastures and has occurred in livestock grazing annual ryegrass crops growing in NSW. and annual beard grass pastures in South Australia and Western Australia. In 1990 this same form of Signs in affected livestock poisoning occurred in NSW in livestock grazing Livestock affected by ARGT, or ARGT-like another annual grass called blown grass. Frequently disorders, display the following clinical signs. referred to as ‘ARGT’ or ‘ARGT-like’, this toxicity kills large numbers of livestock throughout southern • Initially they are reluctant to move. Australia every year. It can rise to outbreak • When disturbed they move with an proportions in some districts in years with particularly uncoordinated gait. favourable weather conditions. • Their limbs appear weak. How do some annual grasses become • Individual muscle movements are rather rigid, toxic? irregular and abrupt, and whole limb movements may be excessively pronounced. The bacterium Rathayibacter toxicus can be carried by an Aguina spp. nematode into the developing • While running they may suddenly fall on their seed heads of some annual grasses, where it knees, brisket or head. eventually produces a powerful tunicamycin–like • When at rest they adopt a wide-based stance, poison called corynetoxin. Poison production occurs sway their head, drool, and experience frequent when the grass is haying off, or ’senescing’. Any muscle twitches. cattle, sheep, goats, horses or pigs that eat • Some may display a backwards and forwards infected seed heads can die. rocking motion. These seed heads may contaminate hay made • Many affected animals eventually fall down, from affected pastures and this hay can also kill the convulse and then get up again. animals that eat it. An ARGT-like poisoning can • Between these convulsive episodes some can sometimes occur in livestock fed water-damaged, appear to be normal but most remain mouldy wheat, but in these cases a different apprehensive, depressed and off their food. bacterium and a different tunicamycin-like poison Mild, forced exercise or excitement can cause a are involved. rapid recurrence of clinical signs and many affected animals will die during convulsions. Grasses affected by the bacterium The death rate from ARGT can be very high. Rathayibacter toxicus most commonly infects annual Wimmera ryegrass (Lolium rigidum), but

Delayed onset of clinical signs In NSW this suspect material should be forwarded to the diagnostic laboratories at the Stock may ingest a lethal dose of the poison during Orange Agricultural Institute for confirmation of the their first day on a toxic pasture but about 4–5 days presence of Rathayibacter toxicus. Outbreaks only will pass before any signs of ill health develop. occur when the infected poisonous grass in the Death may occur within hours of the first clinical pasture has reached a mature stage of growth, signs or not until many days later. Deaths may seed set is obvious and the grass itself hayed-off. continue to occur for up to a week after animals have been removed from an infected pasture. A careful inspection of many seed heads in the affected grass population will eventually reveal the presence of darkish nematode gall enlargements in Autopsy and laboratory findings some seeds and orange-yellow bacterial gall Autopsy examination of affected cattle and sheep enlargements in others. will reveal similar findings. These findings are consistent with this form of poisoning but not conclusive for it. The lungs may be congested and © State of New South Wales oedematous, with froth in the airways. Small focal through NSW Department of Primary Industries 2007 haemorrhages may be present on the surfaces of the heart, the liver may be pale and swollen and ISSN 1832-6668 the brain mildly swollen and congested. Replaces Agfact A0.9.4 Microscopic examinations of tissue sections from these organs reveal changes that are consistent Check for updates of this Primefact at: with their gross appearance, but non-specific in www.dpi.nsw.gov.au/primefacts nature. Disclaimer: The information contained in this publication is The most reliable indicator of the presence of an based on knowledge and understanding at the time of writing (February 2007). However, because of advances in ARGT-like poisoning in livestock is the clinical knowledge, users are reminded of the need to ensure that signs – for example intermittent episodic information upon which they rely is up to date and to check convulsions – together with finding Rathayibacter currency of the information with the appropriate officer of toxicus infected grass seed heads in the food New South Wales Department of Primary Industries or the eaten. user’s independent adviser. Job number 7321 What to look for in suspect pastures During the investigation of a suspect outbreak look for twisted and deformed grass seed heads, some of which may have an orange-yellow exudate forming on them. This exudate soon dries off, but inspection under a magnifying glass should still reveal individual seeds that have changed into swollen, discoloured, bacteria-infected, seed galls.

PRIMEFACT 429, ANNUAL RYEGRASS TOXICITY AND BLOWN GRASS/BEARD GRASS POISONING 2