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This may not apply to yourThis may not apply to your problem but I had a thought or two to share to possibly help you. First, since they are free-ranging...Are you SURE that some are not laying in a nest of their own making somewhere on the property? Chickens, like people, don't always get along so they avoid each other. Maybe there are nests or spots they are using on the land and perhaps, other critters are eating the eggs. Other than that, chicken hens may stop laying if they get yeast, fungus, and/or bacterial infections or get mite infested or sore around their vents. Any kind of stress including fear of other animals (like snakes, etc.) could stop the laying. I recommend looking for things that might be stressing them if they truly seem to not be laying or laying less.

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