I'd be willing to bet I've killed more animals than pretty much anyone on this site - through gamekeeping, farming, deerstalking and over a decade in animal research.
I've been in slaughterhouses and seen normal, halal and kosher methods of slaughter, so will speak from a standpoint of personal experience.
In my opinion, in the modern day, in the UK, there is absolutely no justifiable excuse whatsoever for religious slaughter of animals!
The origins of both methods of slaughter are cultural, and tied in with well meaning methods of ensuring that only healthy meat entered the food chain, it was not possible to pass off sick or diseased animals, as they would be seen in their true state immediately prior to the kill - a perfectly reasonable cultural norm in pre-medieval Abyssinia, not so in 21st century Britain, where regulations ensure the veterinary inspection of live animals both ante and post mortem.
Like it or not, theres more than ample scientific research that shows that pain and suffering is greater in both intensity and duration in an animal that is subjected to exsanguination without stunning, quotes and links below.
Through many years of killing animals for professional reasons, it has always been at the forefront of my mind that respect and compassion for the live animal, and affording it the most humane death possible go hand in hand - even when having had to perform procedures in accordance with defined, regulated and inspected scientific protocols, the level of patience and professionalism that ensured the best welfare standards were upheld in 99.9% of cases was admirable.
The greatest abuses of animal welfare I have ever witnessed come not from hunting or vivisection, but from intensive factory farming
I would suggest that those who feel Halal slaughter is justified go to a slaugherhouse and actually watch it take place, or preferably take responsibility for the consequences of their choices and go and do it themselves;
Finally, I remain convinced that nobody should eat meat unless they have at least once in their lives killed and butchered it themselves and would happily do it again, as I believe that is the only true way of ensuring people understand the value of life and the grave responsibility that weighs on their shoulders every time they choose to eat a piece of meat
http://www.grandin.com/references/humane.slaughter.html
http://www.daff.gov.au/__data/assets/pdf_file/0018/1370331/welfare-sheep-slaughter.pdf
the design of the knife and the cutting technique are critical for preventing the animal from reacting to an incision of its throat. In kosher slaughter, a straight, razor-sharp knife that is twice the width of the throat is required, and the cut must be made in a single continuous motion. For halal (Muslim) slaughter, there is no knife-design requirement. Halal slaughter performed with short knives and multiple hacking cuts results in vigorous reactions of cattle being treated in this manner. Fortunately, many Muslim religious authorities accept preslaughter stunning. Muslims should be encouraged to stun the cattle or to use long, straight, razor-sharp knives that are similar to the knives used for kosher slaughter.
Investigators agree that throat-cutting without stunning does not induce instantaneous unconsciousness. In some cattle, consciousness is prolonged for over 60 seconds (Blackmore, 1984; Daly et al., 1988).
