The first time I remember reading about it was in a book called "Irish Country Ways." I don't recall the author's name but I think it was from the 1930s. I don't remember the mention of butter or lard, but the manure pile reference was there. Donkey poo, though, not cow. What difference it would make would be a question for someone who really knows their sh...uh, I mean poo. Maybe the pile creates an anaerobic atmosphere which affects the way the wood decays (or doesn't as the case may be)
Submersion in a bog would make sense, too, based on what little I know about bog oak.
Fire hardening the stick in the chimney makes sense. You always see survivalists fire-hardening a sharpened bit of wood for a spear or arrow.