A comparison of eggshell mineral composition between cage and free-range eggs via inductively coupled plasma-optical emission spectrometry

Context: In Australia and many other countries, free-range eggs can be sold at significantly higher prices than cage eggs. Mislabelling cage eggs as free-range eggs and vice versa has been documented, and has a significant impact on consumer trust and egg consumption. The development of methods to identify eggs produced from different production systems is necessary to satisfy consumer demand.

Aims: The objective of this study was to determine whether eggshell mineral composition could be used as a way to differentiate eggs originating from each production system. Our hypothesis was that birds with access to soil would have higher levels of trace minerals in shells.

Methods: Eggs were randomly collected from six commercial caged and six commercial free-range flocks in Australia. Twelve eggshell samples from each flock were analysed for mineral composition (Ca, P, Mg, Na, Al, B, Cu, Mn, Fe, K, S and Zn) by using inductively coupled plasma-optical emission spectrometry.

Key results: The results showed that free-range eggshells contained significantly higher contents of macro-minerals (P, Mg and Na) but lower contents of micro-minerals (Cu, Fe, K, S and Mn) than the cage eggshells (P < 0.05). For all minerals measured, a high variability was noted within and between production systems.

Conclusions: Analysis of eggshell mineral composition may not be effective for determining the origin of eggs.

Implications: Systematic studies of the bird’s environment, including analysis of mineral composition in diets, pastures, soil and drinking water are required for comprehensive evaluation of the influences of production systems of laying hens on mineral composition of eggs and eggshells.