shell size for 50 lb prey

[catlynn54]

I have my great-grandfather's 12 ga shotgun along with dove/quail shells.
What size shell should be used for eliminating prey of about 50lb? I mean for instance coyote size or so.

[Villimus Rex]

I would use buck shot. Pretty much any size will do just get them inside of 25 yards to be sure of a killing shot.