My hens all had fertile eggs even at ten years old. I know that Porter's switches his hens out after 4 years old and his toms after 3 years old. I suspect is the problem is toms more than hens.All I have is 1 LED bulb that hangs in their coop and it gets them going lol. I don't trust my girls to hatch their own eggs but every egg I get, I throw in the bator. I've almost always had luck hatching them in the winter. Fertility started going down last year. I thought it was due to having too many toms fighting over the girls but this year, I only have 2 boys and Taz respects Romeo as the boss. I think the issue is that Romeo is being up there in age. He'll be 5 this year (I think?) And several of my hens are really getting up there. Pebbles, Eve, and Sweet Pea will all be 6 years old this year!