Can I found out if my animals were butchered? And if they were, who did it?

I don't think such information is available. If they were in an open area, then fence it off and get the region protected so that other players can't build things to get over the fence. If the area was already protected like such, then there's a possibility that there was a server glitch which deleted the entities from the chunks.

From what I've seen, refunds for this sort of issue are generally not given out due to the workload required for mods to do these refunds fairly, as well as a lack of data to verify exactly what was lost.

Thanks, Darth. My large pasture is surrounded by a 3 high fence. This is the second time this has happened. This time I lost about 50 to 60 sheep, by my estimate. I guess I'll try to build my flock one more time, if I can find any loose sheep wandering around.

Building a fence won't keep people out, even if it's in a protected area, people can "hop" the fence by using the split second the block is placed to hop up and place another to get over, I've watched someone do it to my own animal pens, build a roof over the pen to ultimately keep people out.

I really don't think they were stolen or killed ... I had about 100 animals spread over a 200 x 200+ plot of ground. I logged on and they were there ... left ... came back a little later and they were all gone, except 2 cows and 1 sheep on the extreme south of my property. And the stray animals outside my fence to the north were all gone too. Either someone issued butcher command in my area or a server glitch killed north of a line that cuts through my property.