All of my chickens of different ages and breeds are sneezing very often all day. The oldest ones have been doing it for months and show no signs of there being anything wrong. Laying has not been affected, there is no drainage from their noses, no swelling, nothing out of the ordinary. They are in a healthy environment. Is this just a winter thing? This has been going on for awhile, but has never happened before during warm weather. They are in a draft-free environment with a heat source. Just baffles me. And it isn't a mold problem or fungus.