It's smack in the middle of winter here, and all 4 of our hens are still laying nearly every day. (and we don't have all prolific laying breeds, either!) I think it has a lot to do with how we care for them. We feed the extremely well, allow them to forage for nearly the entirety of daylight hours, and turn a timed heat lamp on in their coop at about 3 am for an hour or so. This keeps them warm and comfortable, which I think is a huge help. We also clean out their run and coop pretty often. I don't know if clean living conditions make an impact on their laying or not, but maybe it does. I know if I were a chicken, I wouldn't want to lay an egg in a dirty place.
For the most part, I think their well rounded diet is to thank for their high production. They get about a large bowl's worth of oats, chicken feed, veggies, and crushed egg shells twice a day. They get a snack of dry oats about mid-day. When we have leftover scraps of meat such as chicken or ground beef, we give them a little of that mixed in with their food for extra protein and fat. When chickens don't get the right amount of protein and calcium, it can make them lay eggs less or completely stop. This is especially true in the winter, when the sudden weather changes can also throw them off their egg game. Just keep an eye on their diets and behavior, and adjust things accordingly. I'm sure they'll be fine!