You need ahve rope in hand ( like gun)[you can make rope from fiber) and you use rope like gun on brahmin untill you succeslyfullcatch it, or till brahmin kill you ;p And you need minimal charisma 3 im not sure but more then Charisma 1.
you cannot have cow if you have charisma 1 why the heck would a cow care about that for ... (yes my char have ch1...)