My three hens are still laying an egg a day and it’s winter? Is it okay?
How old are they? Some pullets (some but not all) skip the molt their first winter and keep laying until the following fall when they molt and take a break from laying. Others molt their first fall/winter and stop laying. Like Aart, I'm guessing that yours are seeing their first fall/winter. (I see you answered while I was typing. And ISA Browns are especially bred to lay a lot so this is pretty typical behavior for them.)
The normal pattern for hens is that they lay eggs during the good weather months, then stop laying eggs and use that nutrition to replace worn-out feathers. The trigger for that is the days getting shorter in the fall. The trigger for them to resume laying is the days getting longer. Some people use lights to stop the days from getting shorter and keep them laying. By domesticating them we've weakened some of those instincts. If you don't play with the lights the vast majority will still stop laying and molt when the days get shorter the second fall/winter if they don't their first fall/winter.
One place domesticating them has changed them is that some do not wait for the days to get longer in the spring to resume laying after the molt. They now start laying after they replace their feathers. This is some of them, not all. Some will wait for the longer days of spring. It's pretty normal for most of mine to start laying after the molt in the dead of winter. I remember one specific adult broody hen that molted in late summer while she was taking care of her chicks and had finished the molt and was laying again by the time the rest of the flock started molting. That older hen laid all through winter.
So with ISA Browns 9 months old, absolutely normal.
