Nearly 70 cattle have died from cyanide poisoning at Old Man Plains research station near Alice Springs.
The cattle died at the site in March, with the 69 deaths caused by eating a native plant, according to a Department of Industry (DITT) spokesperson.
"The investigation has found that the deaths resulted from cyanide in the foliage of spotted emu-bush, a native plant species which can cause toxicity in cattle," the spokesperson said.
Over an eight-day period, 56 breeders and 13 steers died, including cattle that were euthanised when it was clear they would not recover.
"Clinical signs included severe dehydration, difficulty breathing, lying down and difficulty rising," a DITT report on the incident said.
Another 27 surviving animals were trucked to another paddock, while the carcasses of the dead stock were buried in pits on the research station.
Contaminated water and disease ruled out
Research staff checked water quality and the paddock for non-natural sources of poison, but ruled these out as potential causes of sickness.
A vet conducted autopsies, but analysis of tissue and blood samples showed no indication of infectious disease.
Investigations showed cattle had been grazing near a short-lived wetland, which still had relatively green grass around it, even though the water had dried up.
Staff believe cattle ate large amounts of spotted emu-bush (Eremophila maculate), which was growing abundantly around the wetland area.
It appeared cattle ate other species of Eremophila too, but according to samples sent to an interstate laboratory only the Eremophila maculata had cyanide levels above the tolerance of cattle.
Investigation continues
It is not known why poisoning happened this year, but not in previous years.
The department has hypothesised the sudden change to hot weather, rapidly curing grass and time spent grazing in the location where the poisonous plants were abundant may have been contributing factors.
"It is strange that there have been no similar cases in neighbouring paddocks despite them also containing spotted emu-bush," DITT stated in its newsletter.
Department staff are considering installing fencing to stop cattle grazing near the wetland area, planning a survey of the spotted emu-bush and preparing a case study on the event.
There is also scope for further investigations into native plant poisoning of cattle in Central Australia.
The spotted emu-bush poses no risk to humans, but producers concerned about vegetation on their land have been advised to get in contact with the agriculture branch of DITT.
NT Cattlemen's Association chief executive Will Evans said he was not aware of this happening elsewhere in Central Australia.
"In my time in the territory this isn't an issue that we've come across before, we obviously had indigofera poisoning in horses, but in terms of cattle this is new for me," he said.
"I think the government have done a good job in this circumstance in trying to get to the bottom of the issue.
"But it's really important that producers, government, anyone who owns cattle, feels comfortable with coming forward and reporting that an issue's happened and letting people in the region know that this is going on, and that's something they need to be looking out for."
