in dogs and cats, F1 is foundation stock outcross, it does not matter what you breed to, it will be F1. If you are registering purebreds then there are some more detailed steps to follow to go along the line of getting a "purebred" at a minimum of 3 to 5 generations later (depending how many generations the pedigree needs). usually only the Very FIRST outcross used would be a mutt. then ALL of the other crosses are the purebreds breeding back into that mutt. so in just a few generations you can call it a "purebred" again and you only need like 5 or 6 animals, depending on what the registry requires. if you are able to humanely raise a lot of rabbits all at once you could have many different outcross programs at once. When you breed a F1 (AO) to an F1 (AO) you get a BO. If you breed a BO to BO you get a CO. And if you breed a CO to a CO you get a SBT (stud book traditional). So your pedigree would have about 32 great grandparents on it. unless you inbreed to begin with you'd have 16 starter animals, you could use one big giant rabbit male and 8 different unrelated females. so 8 matings, and keep 8 of their AO children. then breed those together for 4 matings and keep 4 BO bunnies to breed together and have 2 litters of CO bunnies, and breed them together to keep 1 and that is your SBT purebred.