I raise Silver Fox in Black and Blue. 6 years now, I breed for show meat and pets.
General rule for Silver fox is 8 months or 8 lbs which ever comes first.
I know other breeders who breed them at 6 months and have had some of the product of the younger breeding's.
Usually a doe bred before 8 months old tend to stay on the small side and have issues kindling.
Silver fox are noted for having large litters between 6 -10 at one time. some smaller younger does will have problems taking care of that many babies as inexperience will usually leave most of the babies cold on the bottom of the nest box.
Your little Blues are very nice animals.
FYI Silver Fox dress out with a 65 % meat to bone ratio, making them one of the better meat rabbits.
Pelting one is the easiest I have ever dressed out. even 10 week old dress out easily.
Enjoy your Fox they are sweet rabbits, wonderful mothers and when you do breed them they make excellent foster mothers for another doe who is clueless when her babies arrive.
Add a black fox if you are breeding and going to use the pelts, the black will stabilize the blue color making it stay the correct color.
http://www.nationalsilverfoxrabbitclub.org/
tons of information at the National Site. please visit and consider joining us Fox enthusiasts.