This only pertains to ferrets indirectly as I am replying to the
spaying/neutering = longer lives.  I think it is an interesting question
but it difficult to seperate from the fact that spaying/neutering also
implies a more responsible and caring owner.  I.e. a person who fixes
their kitten/puppy is more likely to ensure other veterinary care, not let
the animals out indiscriminately etc.  This contributes to longer life than
say just letting a Tom cat roam or a female breed indiscriminately which
can have negative effects.  As to female dogs - it has been proven that
spaying before the first heat will drastically reduce the likelyhood of
mammary cancer.  After each heat the effects of spaying are reduced till
at some point (2 years?) spaying will no longer reduce the likelihood.
 
So many ferrets are fixed young (and for good reason) that it would be hard
to get a database going on long term effects between non-neutering and
neutering.
 
One other thing - people used to neuter dogs and cats around 6 months or
later.  Only recently have people been doing it significantly earlier.  One
thing being noticed is that dogs neutered very early (12-16 weeks say) seem
to grow taller, leggier.
 
Mary, Booker and the fuzzbutts too
[Posted in FML issue 2725]