Good theory (about the humane slaughter), but it's not correct.
Mammals' respiratory function is also driven by oxygen lack, and even
if you remove the CO2, they will still experience air hunger when you
decrease the oxygen.

Consider people who are placed at high altitude (like mountain
climbers without supplementary oxygen).  They will hyperventilate as
the oxygen concentration decreases.  

Same with the folks who suffered execution in the gas chamber.
Despite opinions to the contrary, execution by cyanide gas is not
painless, as the cyanide replaces the oxygen in the hemoglobin in the
blood with a compound which is firmly bound (and thus displaces the
oxygen), and this causes rapid oxygen depletion without accumulation
of CO2.  Victims of cyanide poisoning experience severe air hunger and
then usually convulse before lapsing into coma from the eventual
deprivation of the brain of oxygen.

Probably the best way to slaughter food animals is to do it in the
quickest manner, and this would include beheading; and, as apparently
is done in some places, electrocution to the point of unconsciousness
followed by exsanguination via throat-cutting.

Probably, the quickest method (for large animals) would be a 9mm slug
in the brain, but that is potentially messy and is impractical on a
large scale.  I guess that the other approach is to become a
vegetarian.

Best,

Bob

Robert A. Fink, M. D.
Neurological Surgery
2500 Milvia Street  Suite 222
Berkeley, CA  94704-2636  USA
510-849-2555

**********************************
NOTE:  The material above is not "medical
advice".  Medical advice can only be
given after an in-person contact between
doctor and patient.
**********************************

Well, this method will work only in a modern abbatoir. So why not
use the "Jhatka" method, where the animal's head is severed
with a single stroke of the special knife.

Halal mehod is cruel and barbaric.

Better still - why not let them live and enjoy their life like humans do.

Tam