I've been googling like crazy for this information but really can't find a good answer. Does anyone know what the average productive breeding life of an ASF female is?

I've found information that they generally live about 3 years for the males, about 2 years for the females but nothing on how much of that time she's highly productive. I'd like an idea of when I need to be weeding out the older females to keep the production where I need it to be but can't find a decent answer for this anywhere online.