I have 6 barred Rocks approximately 28-30 weeks old, 3 are laying. I have 2 of the hens that are laying pulling feathers out of other chickens to the point the area around the vent is bare. The 2 picking happen to be 2 of the ones laying. They are fed Purina layeena pellets free choice available all times.And one 12 oz dixi cup of cracked corn a week. The coop is 4'x6' with an attached 10'x10' run . What can I do to stop the picking? 4 chickens have bare areas from this.