Farmers have just been alerted that the wrong variety of swede has been distributed to more than 500 farms.
Due to "human error", the farms received HT-S57 in November last year instead of the Hawestone yellow-fleshed Cleancrop swede.
PGG Wrightson released a statement on Friday that 556 farms received the incorrect variety.
HT-S57, which has since been phased out, is the same variety that caused hundreds of livestock deaths after a mild winter in 2014.
Apart from the difference of yellow flesh versus white flesh, the HT-S57 can become toxic with a mild winter. A mild winter makes the swede go to seed earlier, becoming toxic for pregnant and lactating livestock.
PGG Wrightson seeds general manager David Green told RadioLIVE's Rural Exchange the swede mix-up was a serious mistake.
"We pride ourselves on our quality systems and we are embarrassed this happened," Mr Green said
Since the variety had been sold for the last seven years, Mr Green said most people have used it successfully in the past. He assured that yields will be the same.
Vet South director Mark Bryan commended PGG Wrightson for front-footing the situation.
But Mr Bryan warned farmers to prepare for a mild winter and the potential problems that could arise.
The expert advised farmers to transition cows and sheep more slowly onto the HT-S57 and to keep more feed on hand. However, this could prove challenging for farmers recovering from drought conditions and tight feed budgets.
"It is not a very palatable swede and animals tend to eat the plant and not the bulb and that's where all the problem is," he said.
Newshub.
