The Ministry for Primary Industries says test results showing high toxin levels in herbicide tolerant swedes weren't definitive enough to warrant restricting the sale of the crop to farmers this season.
Hundreds of cows died from liver poisoning and many more became ill in Southland last year after eating PGG Wrightson's herbicide tolerant swede variety.
AgResearch carried out the initial testing on the herbicide tolerant swedes and found high levels of glucosinolates - sixteen times higher than would occur in a natural swede.
Glucosinolates can break down into toxins that cause liver damage in livestock.
Documents obtained by Radio New Zealand show that in October last year the Ministry told the working group investigating the mass stock deaths that the results certainly indicated problems with the crop.
However, the ministry said the initial test results that suggested the high glucosinolate levels were the cause of the illnesses in livestock were actually far from definitive, and could not be considered sufficient scientific evidence to confirm a problem with the HT swedes.
It said it was waiting for a more comprehensive report that it says was due in about a month's time.
The herbicide tolerant swedes were bred to be resistant to the herbicide chlorsulfuron, which will be banned for both sale and use in China at the end of 2015.
The Chinese Ministry of Agriculture have banned the herbicide because of its long-residual effect and its phyto-toxicity to follow up crops.