. I'm assuming the federal government won't think of younger females that have never been bred as breeding females.
You assume wrong.
This has been one of th biggest bones of contention amongst breeders, and on multiple occasions when this has been posed to APHIS they have said that they define a breeding female as ANY intact female. Period. So that would include not just females actively involved in breeding, but young prospects being raised as possible breeding females as well as non-breeding dogs and retired breeding dogs who are not spayed. Some people don't believe in spaying/neutering dogs even if they are not for breeding, or the dog has medical problems that preclude breeding but also make surgery unwise.
We had a wonderful young female we purchased as a puppy from another breeder, but unfortunately she developed epilepsy and then the seizures in turn damaged her heart causing sub-aortic stenosis. We wouldn't breed her, but couldn't spay her either as her heart condition made it likely she would die during surgery. She lived out what, unfortunately short, time she had as a beloved pet here. I guess now maybe it was a blessing that she died in her sleep a few months ago because now, thanks to APHIS, she would have counted against our allowed number of breeding females causing us to have to consider either spaying her against the advice of her cardiologist, find someone we could give her to that was willing to take on several hundred dollar a month medical expenses and a dog who due to the heart condition was unlikely to make it to her 4th birthday, or put her down. We wouldn't have been able to sell her, even if she didn't have the health problems and might have been worth a few dollars, because then we'd have been a dealer for selling a dog who wasn't born and raised here and lose exemption due to that.
APHIS also doesn't take into consideration ownership of the intact female, it's purpose for being at the breeder's, or how long it is in residence at the breeder's. They say ANY intact female, over 4 months old, who resides at the breeders for ANY length of time. So this means that the following would also count against the breeder's number of allowed females:
A female leased for a litter, owned by someone else, who will only be there temporarily.
A female being boarded at the breeder's for the purpose of being bred to one of their studs.
An unspayed rescue or stray that passes through the breeder's home, if even for an overnight as part of a transport.
A female being boarded at the breeder's for any other reason... we have always been open to boarding dogs for friends/family/customers on a short term basis when they are on vacation or such so that they don't have to use a kennel. No more of that if it's an intact female.
Friends/family visiting and staying at the breeder's bringing along their own dog. No more of that either if it's an intact female.
Breeders are expected to take dogs back if for some reason they don't work out or the customer can't keep them, and good breeders are always willing to do that. But now breeders will have to think twice about that if it happens to be an intact female.
The intact females number also refers to females of ANY of the species regulated. So if you have 3 female dogs, your daughter has an unspayed female rabbit as a pet in a cage in her room, and you pick up an unspayed stray cat off the side of the road, you just went over the allowed number for exemption.