Poultry breeder and medical advisor Mike Byron said major supermarket chains will be forced to turn to cage produced eggs if free-range orders cannot be filled.

This backs a recent analysis by the Sun-Herald newspaper which found as many as one in six eggs labelled free-range on retail shelves were cage or barn-laid.

Mr Byron said the current legislation determining what constitutes a free-range egg is being exploited by some unscrupulous producers.

“Currently to have a free-range egg you need a deep litter house and, for three to four thousand chickens, they must have exposure to 12 square metres of sunshine each,” he said.

“Obviously very few of them get exposure to the full 12 square metres but commercial producers then charge a premium price for what they can label a free-range egg.”

Mr Byron also answered some misconceptions about egg production.

“I think overall there is probably little difference between organic, free-range, caged and nutrient fed eggs. There is a market perception that free-range eggs taste better and have more nutrients,” he said.

“Many years ago you could tell the difference in yolks between a free-range and cage egg. A cage produced egg would normally have a lighter yolk.”

But according to the chook breeder, many years ago cage farmers started to feed keratin to the chickens which is a natural substance free-range chickens have access to and turns the yolk a certain colour.

President of Mudgee Poultry and Pigeon Club Bill Robinson said he knows of producers delivering different brands of eggs with different feeding techniques in an effort to create a new market.

Last week, the NSW Greens sought to introduce a rigorous definition of free-range eggs, and the RSPCA backed calls for a mandatory labelling scheme.