New Zealand authorities are puzzled as to how a shipment of beef sent to Taiwan tested positive for a growth-enhancing drug banned in most countries.
The additive ractopamine is used by farmers in some countries to convert fat to lean muscle in their stock in the weeks before slaughter.
New Zealand is one of only 27 countries in the world to allow its use, but restricts it to the pork industry which says it is not widely used here.
Earlier this year, Taiwanese food safety testing detected traces of ractopamine in New Zealand beef at a popular restaurant chain.
Tim Knox, director of market assurance at the Ministry for Primary Industries, says Taiwanese authorities contacted the MPI about their post-border find.
He says a traceback to the farms where the beef came from found no evidence of any offence.
The farms did not stock ractopamine and there were no pigs on site.
Earlier this month Russia announced it would no longer import meat with traces of the drug, causing a trade spat with the United States.
Most countries ban the growth-enhancing drug due to concerns about its impacts on animal and human health.