I haven't tested but given how other farming works the only progress that should be made while you're away is that warm eggs will hatch. They'll probably also become hungry again. Probably best to feed them when you come back for some time, and not bother before you leave since that'll just be a waste of food.

Last time I checked chickens will eat any seeds, making barley an expensive way to go - carrots, turnips, and onions all produce 3 seeds per plant. They'll even eat tree seeds, so if you have them saved up rather than planting a forest or throwing them away then you have stacks of ready chicken feed.