Salam alaikum mufti
Many halal slaughter houses stun the animal before slaughtering it
They use low electric voltage so that the animal loses conciousness but doesnt die
Then They slaughter it the halal way. Is it permissible
Strictly controlled stunning if necessary is allowed if the animal does not die through stunning. If there is a fear or experience has proven that stunning would kill the animal then it would be prohibited to use stunning and the animal if died before being properly slaughtered would become Haram.
There are different forms of stunning that are being used in slaughterhouses throughout the world. Stunning for birds is different from the stunning used for cattle and livestock. If the the stunning method is lethal then it is prohibited. If the stunning method is not lethal and it is reversible then it is permissible.
The lawfulness of the bird's or animal's meat would depend on the fact whether it was alive at the time of slaughter or not. If it was alive at the time of slaughter and it was slaughtered Islamically then the meat would be Halal. If it had died before being properly slaughtered or proper Islamic slaughter was not performed then the meat would be considered Haram.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America