I found some info on a couple of Web pages (in French):

http://perso.wanadoo.fr/solis/textes/abatt.htm
http://www.pmaf.org/

Summary:

To make animals suitable to human consumption, most of their blood has
to be drained (with the exception of game, which is prepared in a
special way).

Since a dead animal loses very little blood, all animals are bled
alive, and die from blood loss. As it is crual to slit a live animal's
throat, most countries have passed a law compelling to stun it
beforehand.

Stunning methods:

1. Cranial percussion by means of a special gun. Widely used for
bovines, it injures part of the brain and induces
unconsciousness. The animal is then hooked and bled.

2. Electronarcosis, often used for pigs. Fainting is induced by
electrods applied on the head. Variant: Chickens' heads are plunged
into water crossed by an electric current.

3. Anesthesia with carbon dioxide. Rarely used, despite the fact that
it is the most reliable method (percussion and electronarcosis, if
applied incorrectly, may fail to anesthesize the animal; or the animal
may wake up after a while).

--Jean-Louis Tu <[log in to unmask]>