As a result of contemplating eventual replacement of my shaving brush, I have been looking into how three sorts of animal hair are harvested — badger, boar, and horse.

A type of badger bristle is used for the finest sorts of shaving brushes, but these bristles are got from killed badgers. As much as I would like a high-quality shaving brush, I do not want to do anything to promote the killing of badgers. (Their populations could be controlled without slaughter.)

Other shaving brushes (like some hair brushes) are made with boar bristles. Most boar bristles seem to come from killed boars, but there is actually at least one firm that shears living boars to harvest their bristles. I'll look into brushes from such a source.

(I can also get a synthetic-bristle shaving brush, though by all accounts these are inferior to natural-bristle brushes.)

I was under the impression that some shave brushes were made with horse hair, but seem to have been mistaken on that score. [Up-Date (2 August): I have indeed found some horse-hair shaving brushes.] In any event, I learned that some horses are raised for the hair of their manes or tails, which is clipped, but that most horse hair comes from slaughtered horses.