Also remember that you will need to rest and replace females from time to time and they can take 3 months to grow up. Also do forget that females nursing will be out of the mix for at least 4-6 weeks..so you'll need more moms to replace them.. I was told by a wise BP Jedi.. that a good rule of thumb is 3 females for ever snake you have to feed plus hold backs, thats 1 Breeding - 1 Nursing - 1 Resting or growing up. So if you have 15 snakes you'll need at least 45 female rats at the least.