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The contamination threat is estimated to have cost Fonterra, the world's largest dairy exporter, more than $20 million.
Although Kerr's jailing sent a message to anyone who might try something similar, Barnett reckoned some exporters were worse off than the convicted businessman.
"There are some out there who will probably look and say, they've invested five or six years into this market and now they're [out of] that market. So who's paid the higher price? Somehow I think some of these small exporters did," Barnett said.
Federated Farmers chief executive Graham Smith didn't hold back when giving a victim statement at Kerr's sentencing in Auckland yesterday.
The 60-year-old's threat, according to Smith, was a "direct attack on the very fabric of society".
Fonterra's Maury Leyland also didn't mince her words.
"It's hard to imagine a worse threat to children and families, or to the viability of our co-operative, the wider dairy industry and our country," said Leyland, who is Fonterra's managing director of people, culture and safety.
Scott Gallacher, of the Ministry for Primary Industries, said the 1080 letter was a "credible threat" to food safety.
MPI informed overseas markets to ensure minimal risk to overseas consumers and the impact on trade, he said.
Had these interactions not been successful, the country faced a real risk of suspension of trade and dairy exports to these markets, he said. It could have caused the fall of up to $4.2 billion in dairy export revenue over a year and a $7.5 billion or 3 per cent reduction in nominal GDP in 2015.