Impact Energy Requirements for Hunting Various Animals

I saw on youtube a guy taking a .177 with 10 grain or so pellets out of a springer/gas ram making a kill shot on a deer head and a pigs head. Would guess the muzzle velocity in the 800fps range due to the fact it was a 1200 foot advertised speed rifle and shot at 50 yards. I think the guys channel was shoot to kill or something like that. Not sure what sized critters the heads came from.