A New Zealand researcher has developed a test that can tell the difference between eggs from caged hens and those from free-range and organic birds.

Developed as a tool to help the industry detect any mislabelling of eggs, it is believed to be the first time that eggs from the different systems can be distinguished by using isotope analysis.

Karyne Rogers of the National Isotope Centre in Lower Hutt, New Zealand, compared different brands of shell eggs produced under cage, barn, free range and organic systems.

She found that almost all the eggs could be differentiated by relating the carbon and nitrogen found in the egg to the hen’s diet.

This was possible as diet directly reflected the type of farming environment where the hens were raised, said Dr Roger.

“Free-range and organic birds have access to a wider range of food sources than caged hens, such as insects, vegetation or organic feeds and this changes the isotope fingerprint of their eggs.”