I have 5 white rocks all less then a year old here recentley i have noticed that 2 of them have a really dirty rear end. they free range at least 5 days a week and their coop is cleaned twice a week. they eat good the two days not free ranging and egg production has not slacked off. what is causing this do they need some other kind of feed . they also get a a big helping of kail every day . could this be causing the dirty rear ends. any suggestions would be appreciated.