Castration involves cutting the scrotum, popping the testes out and pulling them away until they rip out. Here's a nice guide for pigs.
Castrating pigs is a big deal. It helps to consider what intact male pigs (boars) can do:
- Compulsively mount other animals.
- Impregnate females.
- Fight other males for dominance, leading to injuries.
- Damage fences to get to females
- Attack humans more often than barrows.
- Produce meat that stinks when cooked.
Hence almost all male animals get castrated. If only we could engineer pigs that wouldn't have so many male offspring; we'd eliminate castration as a regular and necessary practice.
In Austria some Mangalitsa producers slaughter their male animals before they are too old and have had sex. The idea is that the animals provide usable meet if certain criteria are met - without requiring castration.
It is clear that castration is an unnatural mutilation - this sort of thing doesn't happen routinely in the wild. It is something that humans do to the animal, because we've decided that we don't like funky, fecal-smelling meat as much as meat that doesn't smell that way.
Whenever I think about castration, I wonder what people are thinking when they invent certifications like, "Certified Naturally Grown". How do you naturally castrate a piglet? It is a fundamentally unnatural process - we humans have decided to unnaturally neuter pigs, so we do it.
In general, I have a problem with terms like "naturally grown", because raising crops or livestock is fundamentally unnatural. Just look at the definition of "naturally" - farming is inherently unnatural, as it involves humans bending nature to our will.
Whether it is pest mitigation, castrating pigs, or simply feeding animals (instead of having them fend for themselves), farming is unnatural. Giving pigs, who are cannibals and scavengers, a vegetarian diet is unnatural - as they eat dead stuff in the wild.
If I were to try to imagine the most "natural" hog farm, it would be something like a game preserve - as that would duplicate nature as much as possible. Yet even that would be unrealistic: if the hogs aren't there, how natural is it to dump a bunch of them in some fenced in area?
One might use terms like "non-chemical" or "non-manmade-chemical" to describe certain foods that people think of as "natural" - but such specific terms aren't anywhere as sentimental or marketable as "natural". In general, when I see terms like "certified naturally grown" or "organic", I figure it has some specific meaning, perhaps even a legal meaning - but it probably doesn't mean what I think it means.
My rule for dealing with what to eat is natural (and it is similar to the way pigs behave): ignore the labels, certifications and other unimportant details. If something smells and tastes good, eat it. If it doesn't, don't eat it.
 I have a similar problem with the term Certified Humane, Raised and Handled - the certification allows things that probably aren't humane - but are convenient for humans.