Method for checking label accuracy in barn and free range eggs

The aim was to develop a method for testing whether eggs sold as either 'barn' or free range' were laid under cage conditions. The surface patterns on 11 520 eggs from cage, barn and free range production systems were examined under ultraviolet light for distinctive fluorescent marks associated with each production system. In addition, the effects of egg washing, egg size, condensation and cage dusting on the prevalence of the fluorescent patterns associated with the cage production system were examined. The prevalence of fluorescent white double parallel lines with 2.2-2.5 cm spacing was a distinguishing feature for eggs laid on wire floors in cages. If five or more eggs in a sample of 90 eggs have double fluorescent lines it can be concluded with greater than 999 in 1000 probability that the batch contains some cage-laid eggs. Dust from the egg collection area below the feed trough was the main source of the fluorescent material. Washing the eggs removed or obscured the double lines. Egg size and condensation had limited effects on the prevalence of double lines. Infrequent dusting of the wire floor did not reduce the value of the test.