A jill is capable of having two litters in a year.  An average litter may is 6-8 kits, there may be as many as 12 kits in a litter.  A ferret can breed at 4 months and up. If females are not bred, they can develop a condition that is often fatal, as they will not ovulate until bred and will stay in heat perpetually. This seriously affects the health of the female. There are also problems with lactation and mastitis.

Over-population of ferrets can and should be avoided with proper spaying or neutering.

Neutering drastically reduces the odor of a male, prevents him from marking his territory with smelly slime, and makes him less aggressive (males in season may kill other ferrets, even females).  Spaying saves a female's life, since once she goes into heat she will need to be bred or she will almost certainly die of anemia.

A female can be spayed even after she goes into heat, but if she's been in heat for a month or more, your vet should do a blood test before the surgery.  Females can be brought out of heat without
becoming pregnant with a hormone injection or by breeding with a vasectomized male, either of which will lead to a false pregnancy which will last long enough to let her be spayed.  Neither one is a good long-term solution, though.

When ferrets breed it is very rough! The male will dig his teeth into the scuff of the female so she will not run away. Even though her skin is tough in that area, continual mating can cause a lot of cuts and abrasions. This means that you will need to separate the ferrets once mating has taken place. Ferret breeding is very noisy, with the female screaming and the male chattering very excitedly, even angrily!

Jills tend to have problems giving birth, producing milk, and so forth.  If you're serious about breeding, talk to someone who has first.

Some Questions to ask yourself  if you are considering breeding ferrets:

• Can you get them altered to sell as pets?
• If so, what is the cost?
• How much does it cost to feed a ferret per year?
• How about waste disposal?
• Can a person get one at a pet store cheaper?
• If not altered, will they make good pets unaltered and is it humane?
• Will they end up in shelters because someone told you they would have the ferret altered but then said "it stinks and I don't want it." Will the breeding be indoors or out?
• Are you prepared for the smell of indoor breeding and the difficulties of outdoor breeding?
• Do you have a USDA license to sell them and are they legal in your area to own or breed?
• What vaccinations will they need and what is the cost?
• Will you have enough jills to foster out kits as needed?
• Will you have enough ferrets for genetic diversity?