I remember that once, a Facebook page was hacked into (I guess) and started posting pictures and stories about tortured animals. Everybody went WTF and the page was shut down a few days later.

4chan all just like animals

I've never been there, but plenty of people on the internet do. Facebook pages against vivisection etc. seem to get way more likes than those in favour of it, the meme that humanity had better become extinct because wildlife would be better off is quite widespread, and some people even rejoice when a hunter dies (though this is a minority stance).

How often does 4chan torture animals?

Not often. Hurting animals is generally considered Not OK on 4chan, to the extent that anything is Not OK on 4chan.

There are a few pictures and stories that get passed around (some kids kicking a cat against a wall like a football, shoveldog, etc), but many fewer than the human gore pictures. 4channers mostly aggregate this stuff from all over and post it to be edgy and drive people who aren't edgy enough away from 4chan.

And yeah, to the extent that people do torture animals in current events (as opposed to past stories), vast hordes of moralfags and raiders from 4chan tend to hunt them down and ruin their lives.