I am not a breeder nor a vet, but the way I understand it...
 
If a Jill comes into heat and you want to spay her and not have babies, the
most appropriate response is to utilize the services of a vasectimized hob
to take her out of heat, wait a few weeks, then do the spay.  While you can
spay a ferret while she is in heat, there is a slightly elevated chance of
bleeding or other complications due to the increased hormone levels and
blood flow to the pelvic area.
 
We have a rescue here that we are playing the waiting game to see if she is
whole or not.  The above will be our response if she is.
 
-Anne
[Posted in FML issue 2040]