At the time of Shechita the carotid arteries serving as the central route carrying blood through the neck to the brain is severed. The instant the knife passes through these arteries, blood flow to the brain ceases, blood pressure drops rapidly, and the animal looses consciousness within two seconds, if not sooner!
On the other hand, non-halachic (not according to Jewish law) forms of slaughter undoubtedly cause pain to animals. Even numbing the animal with an electric shock, which supposedly prevents any feelings of pain, actually only "fries" the beast's brain, and certainly causes unnecessary suffering. And of course, death through a bolt to the head surely engenders suffering in the animal, especially if delivered inaccurately, whether due to poor aim or an unexpected movement of the animal's head. In these cases, levels of pain are far from minimized, and in fact, greater and unnecessary suffering may take place."
It is also worth noting the medical opinion of Dr. Temple Grandin, a worldwide expert on proper livestock handling, who has developed various techniques to decrease animal suffering both on ranches and in the slaughterhouse. Dr. Grandin claims that the major suffering incurred by animals in the slaughterhouse is not in the moment they are killed, but from their improper handling from the moment they arrive until their deaths. According to her findings, if cattle are handled properly, they reach the point of slaughter relaxed and well behaved. Because, in the case of Shechita, the actual slaughter is painless, it is clear that proper handling erases the only other chance for animal suffering to take place.
There is still more.
Meat slaughtered for consumption must be kept hygienic and safe throughout the duration of its storage, both for health reason – to avoid food poisoning – and economic ones – so as not to needlessly waste food. In general, the higher quality the meat and the fresher it can be kept, the less needs to be discarded and the fewer animals need to be slaughtered. According to some researchers, Shechita ensures higher quality meat than other forms of slaughter. Shooting, for example, leaves an excess of blood in the carcass, due to the time lag between death and the bleeding of the carcass. This causes the meat to spoil faster. In other non-halachic methods of slaughter, the situation is even worse. (With regard to this topic, we should note the halachic requirement to salt meat after slaughter in order to extract the remaining blood. This act is derived from the prohibition against consuming blood – primarily a spiritual commandment, which has obvious health benefits as well.)
I have one more question that needs attention. Why, if Shechita is painless and the most humane to kosher animals, is the world so blind that it wants it stopped? Simple answer, Hashem is sending a message to the Jews "It is time to come home." If, eventually, the only place in the world that a Jew can be a Jew; serve Hashem and observe all of the Torah is ISRAEL, (you finish this sentence). Thank you Hashem – Your message is clear.