When the weather started getting colder last month our chickens just completely stopped laying. They still have a warm coop and always have food and oyster shells available but they just stopped. We have 2 groups of chickens the first group is 1 1/2 yrs old and the other group is only about 1/2 a year old. We used to get an egg from each of our chickens daily, before they stopped. Any ideas on why they stopped and how to get them started again?