The real question is: at what age wer your ferrets spayed or neutered?
If you have intact ferrets then adrenal gland disease is very unlikely
because the ovaries or testicles will respond to the LH and make the LH
receptors on the adrenal glands nonfunctional.  If you waited till after
they went into heat before you spayed or neutered them, then same thing
happened.  The ovaries or testicles producing the sex hormones maked the
LH receptors on the adrenal glands nonfunctional.  However if they were
spayed or neutered at 4-5 weeks of age (neonatal) just like pet ferrets
here in the USA, then keeping the lights on day and night will increase
the LH level and add to the stimulation of the adrenal glands.  This
chronic over stimulation of the adrenal glands eventually causes adrenal
gland disease to develop.
 
Are your ferrets intact or fixed?  and if they were fixed, at what age
were they fixed?
 
Jerry
[Posted in FML issue 5062]