I tamed a level 40 mammoth, no cheats/tame boost on settings. It ate 100 mejoberry (it said 250 on here) but I needed 102 because spoil times a bummer. It also took 7 narcotics not 76 like it said here. Unfortunately didn't pay attention to how many tranq arrows it took. Hope this helps :)
On the raft build a 3x3 foundation with 3 walls high and a ramp going up into the raft. Go to the winter area youll find Mammoths there. Get it into the raft. Once in the raft shoot it with tranq arrows. Starve it and then feed. Kibble is 80times its food.