One of the known things, which is also why I don't know many vets who'll
neuter or spay a dog under six months, is that sexual hormones are
nessisary, especially in males, for proper and full adult growth.  Early
neuter ferrets lack the muscularity and sexual dimorphism of non-neutered
or 4 months-1 year neuter of other ferrets.  Another concern is that
they're small animals and sometimes the job has been incomplete,
especially with females, when done by techs doing hundreds of animals
at a large breeder.  For some time, Hagen ferrets in our area were
constantly going into heat, which the less informed owner was left doubly
unprepared for since they had been told their animal was neutered, as
were the local vets who often weren't used to ferrets and didn't realise
it was a case of part of an ovary being left in.  The other health
concerns are things I don't feel qualified to comment on, but I think
both these reasons make it reasonable for people to prefer ferrets to
be neutered at an older age.
 
Melissa Smith (nee Drake)
http://www.blueskunkland.com/ferret (the Wooze Crew)
http://www.blueskunkland.com/ferrettoons (over 20 designs on over 30
products for the holidays!)
[Posted in FML issue 3996]