The deaths of more than 100 dairy cows at a Jersey farm were not caused by notifiable diseases, according to the island's government.
The cattle at Woodlands Farm, St Helier died from an unknown cause in mid-December 2022.
Animal tissue samples taken by the farmer’s private vet were sent for analysis immediately after the incident.
A number of possible diagnoses that can cause high mortality in cattle have now been ruled out.
These include notifiable diseases such as anthrax, BSE and foot and mouth disease.
Samples of the feed taken by the Jersey government’s Natural Environment team are still being tested at a laboratory in the UK.
The findings of the initial testing on the animal tissue samples are being used to help focus the secondary testing.
This is likely to take some time and may not be conclusive, the government said.
Director of Natural Environment, Willie Peggie, said initial findings confirmed that the deaths had been an isolated incident.
"We have a working theory and strong confidence in what caused the cows to die so suddenly," he said.
"However, it would be unprofessional, unwise and without scientific rigour to state that publicly just yet, until the further testing of the feed is complete."
Mr Peggie added that the testing of feed samples were ongoing at the laboratory, and results would "take some time".
"The testing is a process of elimination, and this means that the most we may be able to provide is a likely explanation of the cause, rather than one that is absolutely definitive."
