Hi Shelley,
I only have breeding experience with ferrets kept outdoors under natural
light conditions in the UK.  I have not had it in my business but friends
of mine have had ferrets which come back into heat 3 or more times a year.
Over 30 years I have only had jills come into oestrous once a year, usually
around March.  It was three years before I learnt that they were not
supposed to be left in heat all summer, It was when my first jill had to be
helped over the bridge aged only three and a half and a friend asked how
her kits were doing.  He told me that it was better to breed every year.
She had had two summers in full heat.  Back in the 60s and 70s before the
jill jab and vasectomiesed hobs it was not that uncommon for jills to be
left in oestrous for five months they lost a lot of condition but did not
normally die if they were in good condition and well fed ( which a lot of
ferrets were not ).  At that time the average age for a ferret was only 4
to 5 and Snowy had a large cancer on the side of her neck, which I do not
think had anything to do with being left in heat as her brother died the
same way 18 months later.
 
I never spay my jills, if they are not going to be used for breeding they
are given a jill jab at the end of March, I have been told that this should
not be done but one of my jills has been jill jabbed 10 years in a row and
is fine fit 11 year old and is always the first ferret in the food bowl in
the mornings.  Hope this info helps.
 
Chris
Wessex Ferret Club    www.wfc.cwc.net
[Posted in FML issue 3217]