Ryegrass Toxicity
Ryegrass is a pasture, often mixed in with meadow hay that is fed to horses and other livestock. Although mainly safe, it has the potential to cause fatal poisoning if the ryegrass is toxic. Annual ryegrass toxicity is most commonly seen in Western Australia over the summer months with feeding of hay contaminated with infected ryegrass seedheads. The infection is caused by a toxin-producing bacterium Rathayibacter toxicus which is carried into the ryegrass by a nematode Anguina funesta.
WHAT SIGNS TO LOOK FOR?
The toxin is cumulative and so signs do not appear until a near fatal dose is ingested. The time taken for clinical signs to appear depends on the amount of hay being consumed and the amount of toxin present in the seedheads. Occasionally animals may die before symptoms are noticed. Common signs include
- Weakness
- Un-cordinated gait
- Diffuse mild to severe muscle tremors
- Staggering
- Collapse
- Convulsions and eventually death
Signs are brought on by stress or activity so it is important that horses suspected or confirmed of having ryegrass toxicity are handled and moved quietly. Unfortunately there is no specific treatment for horses with ryegrass toxicity other than supportive care. Symptoms may be intermittent and often if the symptoms are mild, they may recover and appear normal before experiencing another episode. Not all horses developing clinical signs will die, with recovery taking up to 2 weeks.
If you suspect your horse may be affected you should ring your veterinarian straight away. Minimise any stress or excitement and remove access to suspected toxic hay from all animals.
HOW TO PREVENT CONSUMPTION OF TOXIC RYEGRASS
It is strongly recommended that all stock owners and feed store merchants ensure meadow hay containing annual ryegrass is tested for the presence of the bacterium that causes ARGT. The bacterium cannot be detected by simple visual inspection so the hay needs to be tested in a laboratory. Annual ryegrass and hay sampling and submission kits can be obtained from Department of Agriculture offices. Other types of hay such as oaten or Lucerne hay do not normally contain ryegrass and should be safe to feed.
