While I can appreciate both sides of the Neuter/Spay debate, I just want to elaborate on one of the reasons it is so risky for small animals of any kind (small being the factor).
Anaesthesia is hard on large bodies, if not calculated correctly (and sometimes, even if it is correct), therefore, it is a huge jeopardy to the tiny little bodies of our pigs, ratties, puppies and kittens, young rabbits and so on. This isn't to say that it shouldn't be done, though. An
experienced Exotics or Small Animals Veterinarian can greatly minimize the risks and it is important to have one of these in your corner anyway. (I always ask "how many surgeries have you done on 'such and such' animal? .. and how many of those were successes? ...and why weren't the others?"
I have a few ratties here, and it becomes necessary for unruly boys.. bloody, ripped flesh, missing toes kind of "unruly" ...and it's a great preventative measure for mammory tumors in females (which is seemingly inevitable with female rats from
any background).
I do not have my ratties altered just "willy nilly", though. (and I won't have it done to Giorgi, the piggy, if he and another male ..still looking... can get along well enough) If I have a "bad boy" that is creating a horrific situation for everyone involved, then he gets the 'snippity snip'. If I discover the tiniest "growth" of any kind on a girl, she gets a check up and a diagnosis from the Vet, as to whether she really needs to be spayed (to try and avoid future tumors), or just have that one removed, etc. .
While there have been many studies done on humans and the effects of having hysterectomies, etc. ...hormonal imbalances and such... there isn't much evidence (published scientific studies available to us.. as laymen or hobbyists) to suggest this with small animals. From experience, it certainly doesn't decrease their lifespan (short of surgical or post surgical complications, that can happen to even the healthiest animal).
Just my $0.02