I keep mine on the grower feed(18%protein) and offer oyster shell free choice. I believe most layer feeds are 16%, unless you get it from a feed mill. I have read that they eat more in the winter to keep body heat up. Increasing protein can do this.
How old are they? I noticed mine did that right before they started laying. Then it stopped after about a week. I think it is a protein issue, body using a little more for egg production.