In theory you could hit a boar with 1 Marksmanship, you would miss about 98% of the time however. But, I have around 50 Marksmanship and hit a X bear 95% of the time.
i kill lvl 1 stuff easy with lvl 15 markmenship. if i was a betting man, try gettin it to lvl 30 and make sure you have some good Q bow and arrows, and then try ur luck.