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Vets blamed a variety of herbicide-tolerant swedes for the cow deaths.
DairyNZ regional team leader for Southland/South Otago Richard Kyte said blood and autopsy samples DairyNZ collected from dairy cows that grazed on swedes in Southland show the cows suffered liver damage this year consistent with the liver damage associated with swedes.
He said liver damage was observed in cows across a variety of swedes, but DairyNZ could not rule out an ''unknown toxin''.
He said the information from the blood samples and autopsies was limited.
''Because we were late, the sample was quite skewed, so we can't draw any conclusions from that at all,'' he said.
''While the study did not allow comparison between swede varieties, the findings indicate that cows experienced liver damage after grazing [on other] swede varieties as well as the HT (herbicide tolerant) variety, regardless of whether there were visible signs of illness,'' Mr Kyte said.
He said results expected in March from an ongoing survey of 120 farmers - both affected and unaffected by the unexplained illnesses - would further the industry group's understanding of what happened to Southland dairy cows this year.
''Understanding on-farm management practices is a vital piece of the jigsaw,'' he said.
''We have also sought permission to access their relevant veterinary records.
''These could provide a wider dataset and help us understand the illness better and give us valuable insights into what happened this season in Southland.''
Southern vets reported seeing liver-damaged cows dying in mid-July and shortly afterwards concluded a herbicide-tolerant swede was a likely culprit.
More than 200 cows were said to have died this year and others were suffering from liver damage and sensitive and peeling skin.
At a cost of about $2000 per cow, and ongoing veterinary costs for animals that survived, the hit to Southland farmers was expected to be big.
The survey results are expected in March.
An analysis of plant samples is expected to begin in February.