Religious slaughter evidence

[Napoléon]

For me it's a darn no brainer that it causes unnecessary suffering.

But if you really need some 'evidence' a wiki article I have used before has some sources of investigations into the act:

In the United Kingdom, the government funded but independent advisory body Farm Animal Welfare Council recommended that conventional Ḏabīḥah (along with Kashrut slaughter) without prior stunning be abolished. The FAWC chairwoman of the time, Dr Judy MacArthur Clark, said, "This is a major incision into the animal and to say that it doesn't suffer is quite ridiculous".

Various research papers on cattle slaughter collected by Compassion In World Farming mention that "after the throat is cut, large clots can form at the severed ends of the carotid arteries, leading to occlusion of the wound (or "ballooning" as it is known in the slaughtering trade). Nick Cohen wrote in the New Statesman, "Occlusions slow blood loss from the carotids and delay the decline in blood pressure that prevents the suffering brain from blacking out. In one group of calves, 62.5 per cent suffered from ballooning.

http://en.wikipedia.org/wiki/Dhab%C4%AB%E1%B8%A5ah

It has a section on 'controversies'.