How come my neighbors eggs are always poopy on the shell? He has 26 hens of various ages from 7mo-7yrs. My pullets laying for almost 2 weeks now always have clean poop free eggs. Why is that. The only things we do differently is I have single bird nest boxes and he has a 3 foot long "communal" nest area. Also I put ACV in my birds water. Any clue as to the different outcomes?