If it is true that...

The American cat population is estimated from 60 million to >100 million

and

Cats live ~15 years

Then it must be true that...

To maintain the cat population, the annual birth rate must be 4–6.6m cats

If it is true that...

To maintain the cat population, the annual birth rate must be 4–6.6m cats

Then it must be true that...

To merely be the majority source of cats, breeders would need to produce several million cats per year, every year, without fail