You must learn a special skill to tame Blood Beasts. It is taught by a Blood-Soaked Tome of Dark Whispers, a guaranteed drop from Zul in the Uldir raid on Normal Mode or above (i.e. not LFR). Once learned, this skill is account-wide.
Location & Notes:
Located in Abandoned Ruin, Nazmir. This tick spawns during the search of the Abadoned Ruin in the Horde zone quest The Shadow of Death.