Horses are firming as the prime suspect in the mystery poisoning of dogs in Victoria.
More than 20 dogs are known to have died and dozens more became severely ill after eating pet mince in June.
The dogs have died from liver poisoning caused by indospicine, a toxin never seen before in the state.
Agriculture Victoria says test results have confirmed pet meat processed in Gippsland as the likely source of the toxin.
"Horse meat is emerging as the focus of the investigation into the indospicine toxin found in pet meat products," the Victorian government said in a statement late last week.
"PrimeSafe and Agriculture Victoria are now aware of a consignment of horses that came to Victoria to be processed for pet meat from the Northern Territory where the Indigofera plant that contains indospicine is known to grow."
Read also: COVID-19's impact on NSW: the numbers
Feral horses and camels from the Northern Territory outback graze on the plant and have caused toxicity problems before.
It is believed there are more than half a million feral horses roaming free across the outback.
In Victoria, horses can be legally used in a knackery for use as pet food in accordance with the Australian Standard for the Hygienic Production of Pet Meat.
"Testing and gathering information continues, and is now focusing on identifying any further distribution of the indospicine contaminated pet meat, and on gathering lessons from this rare event," the government statement said.
Read also: COVID changing home trends living costs
Dog owners are reminded not to feed their pet any fresh or frozen raw pet meat sourced from the knackery between May 31 and July 3.
All kinds of pet meat should be considered at risk of indospicine contamination, due to the blending of pet meats, including products described as beef and kangaroo pet meat.
Officials fear pet meat contaminated with indospicine may still remain in circulation, despite voluntary withdrawals by the pet meat processing facility and recalls by pet meat retailers.
Businesses and dog owners are encouraged to check the source of their pet meat.
If unsure, owners are advised to contact their pet meat supplier to check where and when their pet meat was sourced.
Some products will be labelled as Maffra District Knackery and Backman's Greyhound Supplies, a government spokeswoman said.
"After initial distribution, the pet meat could have been processed into a variety of products making identification of all affected pet foods difficult.
Since the end of May, government agencies have been made aware of 61 affected dogs, of which 21 have died.
These cases are predominantly in Bairnsdale, Traralgon, Mornington Peninsula and eastern suburbs of Melbourne areas to date.
Indospicine was confirmed as the toxin causing the illness and deaths on July 23.
Indospicine is a toxin found in native plants of the Indigofera (Indigo) species across Australia, but the species that produces high levels of the toxin is found in northern Australia.
The toxin has been previously shown to build up in the tissue of some grazing animals when they continue to eat these plants and dogs are especially sensitive.
Indospicine toxicity had not previously been reported in Victoria but has been reported in northern Australia when dogs eating horse or camel meat were affected.
There are no indications of any risk to human health nor of human food safety issues associated with these cases to date.