A couple things to mention:

1. This guy cannot be knocked out by simply shooting him with tranqs. You need to get him to stand up on his hind legs. The best way to do that is to punch him (and keep punching him every now and then to maintain agro as he loses it fast, don't shoot him to do this as youd just end up killing him despite his high HP. Once he is on his hind legs keep your distance and shoot his Hind legs to deal torpor (as long as he does this he'll take reduced damage to them) The higher the damage you deal the more Torpor you do. The best weapon to do this is the Fabricated Sniper, Fabricated Pistol or Assault Rifle as it lets you space your hits properly to avoid hits when he is in his knockout animation (which has him sway slightly and then fall over on his sides, it's quite hard to tell when the torpor is full so wait a 1-3 Seconds in between shots.)

2. He loses torpor very fast when he goes back down to walk normal again. So try getting him into Bipedal stance again as fast as possible.

3. Once he's out be aware of Torpor drain roughly equal to a Giga

4. He eats Exceptional Kibble and above, Berries and Crops however Kibble is the only real way to tame him as he only gets about 0.1-0.5% taming progress from Berries and crops and you'll go through your entire Narcotics supply trying to keep him down if you go for them.