Fonterra says it won't be changing its testing for nitrate levels in dairy products, despite China rejecting more than 40 tonnes of powder for failing the test there.
The powder was tested and cleared for export in New Zealand, but did not meet testing specifications when it arrived in China.
Food safety and quality group director Ian Palliser said that could have been down to the normal variations in test results, and there's no need to change it.
He said there is a limit of two parts per million in China and the product was tested at somewhere between 2.4 - 2.8.
Mr Palliser said when the product left New Zealand it was testing at somewhere between 1.4 - 1.8 and was therefore within specified levels for both New Zealand and China.
He said it may be variations in testing mechanisms.
"We are not changing our testing methods because we believe they are quite acceptable as they are, this is a case of a product has gone off specification in transit, we don't understand why."
Mr Palliser said the product was removed once they agreed with the Chinese authorities that it was out of specification and it's been returned to New Zealand and used as stock food.
He said the product has been taken out of any form of human consumption.