Scientific data supported the possibility substances in the swedes caused the mystery illnesses.
But the possibility of an unknown toxin causing the problems could not be discounted, DairyNZ Southland/South Otago regional team leader Richard Kyte said.
“However, we have to be careful about drawing any major conclusions from these findings.
“The analysis is based on samples collected at a single point in time towards the end of the period when the illness was evident.
“They were not collected over the whole swede grazing period.
“Additionally, only a selection of swede varieties was represented in the animal samples taken.
“The findings appear to be consistent with known liver damage associated with cows grazing brassica forage crops, except the visible signs of illness seemed to be more severe,” he said.
“While the study did not allow comparison between swede varieties, the findings indicate that cows experienced liver damage after grazing swede varieties other than the HT (herbicide tolerant) variety, regardless of whether there were visible signs of illness.
“The nature of the liver damage is similar to that seen in outbreaks of facial eczema with visible signs such as photosensitivity occurring after the liver has been damaged.”
All brassica varieties produced a range of sulphur-containing substances (pre-toxins) such as glucosinolates and SMCO (S-methylcysteine sulphoxide) which were not toxic in themselves but brassica pre-toxins were changed during rumen digestion into toxic agents such as nitriles.
Nitriles were known to cause liver damage in rats.
Levels of glucosinolates and SMCO in plants could be affected by plant growth conditions and were generally highest in mature plants and flower heads.
The next step in the investigation was to collate and analyse the data from an in-depth survey of 120 farmers and their graziers. The survey was in the process of being completed.
“We have interviewed farmers across the region, both affected and unaffected by the issue, to help us understand whether farm management practices may have been a contributing factor,” Kyte said.
“Understanding on-farm management practices is a vital piece of the jigsaw and we really appreciate the time and support farmers have provided us by completing the survey questionnaire.
“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.”
Analysis of the survey data had now started with findings expected in March.
To help understand how affected cows had recovered, an analysis of more blood samples was also under way. Findings from that analysis were expected by the end of February.
The analysis of plant samples was expected to begin in February.
“We are working with NZ plant breeders and laboratories to ensure we use a consistent methodology for the analysis of the plant samples. That’s vital to ensure we get some robust and useful information from that work,” he said.
