Hello,
I started out with 7 RIR, 3 Leghorns, and one Australorp (that's 11 total)...all the same age..a year and a half ago. They get along pretty well and I was getting 8-9 eggs a day minimum when they hit their stride. They have been through one winter. I put a light bulb in the coop and...
I put a 60 watt fluorescent in my coop. I leave it on 24/7. My 11 hens (they are all less than a year old) have averaged 7-8 eggs a day all winter. I am in north-central Missouri. It gets cold here. Down to 0 some nights. I have 7 RIR, 3 Leghorns and one Australorp.