The last copra toxin scare was in 2007 when Fonterra ordered its farmers to stop feeding out the coconut husk derivative after finding elevated levels of toxins in milk.
After the 2007 scare, the dairy industry and feed manufacturing industry developed a best practice guideline to manage the use of copra cake by dairy farmers.
Fonterra says the latest incident is tiny by comparison to the 2007 one.
Only one shipment
Routine weekly testing and surveillance for copra aflatoxins by Fonterra late last month picked up a slight increase in the milk from 26 farms nationwide.
The company and four feed merchants reacted quickly and traced the contamination to one shipment, said Fonterra food safety and sustainable production manager Andy Goodwin.
The level of aflatoxins in the affected milk was "very small" and "miles" under the European Union safety standard threshold, Goodwin said.
Copra has been increasingly imported as a feed supplement for dairying in recent years but in small quantities compared to palm kernel.