Did the breeder tell you they were so many months old when you got them?
It's been observed that ASF's have around 10 litters before the numbers drop off sharply and stop producing, we're these ones very small and just weanlings when you got them, or were they just about the same size as they are now? I ask because like Mike, you may have not gotten fresh ones if the production suddenly fell.
What are you feeding them, and how is the protein and fat percentage? Is it a standard diet and do you give them anything extra?