The core condition of valid dhakāh is that the animal is alive when the neck is cut and that blood flows out; Allah forbade "that which is killed by a blow" (al-mawqūdhah) except "that which you slaughter [while still alive]" (5:3). Therefore stunning is only acceptable if it is a reversible method that does not itself kill the animal — so that, if left un-slaughtered, it would recover — and the animal is then properly slaughtered while still alive; a stun that kills renders the meat harām carrion. Many contemporary scholars permit such reversible stunning under strict conditions, but because it is hard to verify in practice, the safest and best course is un-stunned hand slaughter, in keeping with the Prophet's command to perfect kindness in slaughter: "When you slaughter, slaughter well, and let one of you sharpen his blade and spare suffering to the animal."
Q&A · Health & Halal Food
Is stunning an animal before slaughter permissible for the meat to remain halal?
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.