Make sure you have the area well walled off with the log walls before defeating Elkthyr. I did a similar thing figuring out how to breed boars, though had no way to slaughter them til I found out about the butcher knife. Beat the big elk (By then I had fully upgraded leather and decent archery skill) However was completely unprepared for my first "Forest Moves" event, had never even read about it.. It didn't go well for me or my Boar farm. :(