A New Zealand scientist has developed a test that can prove whether eggs come from caged hens or from free-range or organic production.
Dr Karyne Rogers, a senior scientist with GNS Science's National Isotope Centre in Lower Hutt, analysed off-the-shelf eggs from caged, barn, free-range and organically raised hens.
By measuring carbon and nitrogen levels in the eggs, she could link them to the hens' diet, which reflects the farming system used to raise them.
Dr Rogers says the technique is a good way to scientifically prove that eggs are truly free range or organic and could be used as an effective verification tool to guard against mislabelling.
She says New Zealand exports more than two million free-range eggs a year and this test could provide greater consumer confidence, giving the industry an advantage in export markets.
Egg Producers Federation executive director Michael Brooks says the test may also be a useful tool for accreditation agencies and it will talk to Dr Rodgers about her findings.
However, he says egg producers also have some questions about the effectiveness of using diet to differentiate free-range from cage produced eggs.
"That is an issue that needs some further consideration ... Industry nutritionists would wish to explore that topic further to ensure that's the basis of the findings, and it's really important that that's clearly understood by the industry and by Dr Rodgers in terms of doing this work."