Taming a equus is a passive tame not a knock out. You'll need to make a trap so it won't run off and get killed. You'll need as much berries as the DeX says. And have a ghillie suit to not spook it.But in case you accidently mount off and lose some taming effect have some more berries with you just in case. This is how I did it.

More Equus Taming & KO Tips