Review of stunning and Halal slaughter

Summary

All forms of stunning are a means to induce a state of insensibility in an animal about to be slaughtered. Done properly it will achieve this aim immediately and render the animal's brain unable to process the noxious stimulus associated with the stun before the information actually arrives in the brain. The insensible animal then needs to be effectively bled (killed) before the effect of the stun wears off. 
There are two forms of pre slaughter stunning used for ruminants mechanical and electrical. Mechanical stunning can be achieved by either captive bolt or free projectile. Either form requires correct shot placement for effective stunning. Electrical stunning is achieved by passing an electrical current through an animal. The pathways most commonly utilised in the pre-slaughter stunning of animals are head-only, head to brisket, and head to body. 
It is important to note that for animal welfare reasons no current should pass through any part of the body before current has passed through the brain. This is to ensure that the animal is rendered unconscious before the cardiac arrest is induced, as this would otherwise be very painful. With all forms of stunning fast and effective bleeding is an essential part of the slaughter process. It is usually achieved by opening major blood vessels and the bleeding technique is specific to each species. If the meat is to be used for human consumption the removal of blood from the carcass is very important to ensure product quality and shelf life. If religious slaughter is to be performed without prior stunning there are a number of important considerations in order to minimise any suffering of pain and distress by the animal. Above all the animals need to be handled quietly and restrained in the least uncomfortable manner. Subsequent slaughter has to be initiated without any delay and in a manner that ensures maximum blood loss in the shortest possible time. 
After the cut the slaughter man needs to ensure that both carotid arteries have been severed completely and that there is a gushing blood flow from them. If for any primary (incomplete severance of carotid arteries) or secondary (carotid occlusion) reason the blood does not flow freely from both carotid arteries then the animal should immediately be stunned with a penetrating captive bolt gun. If this is not done there would be an unreasonable delay to the onset of insensibility. 
There are two main considerations for assessing the impact of non stunned slaughter on the welfare of an animal: 
1. Does the neck cut cause pain? 
2. How long does it take for the animal to lose enough blood for insensibility to occur and for any perception of pain or suffering associated with slaughter to disappear? 
The overall conclusion from latest research is that the neck cut is associated with noxious stimuli that are likely to be perceived as pain by a conscious animal. The shortest period from neck cut to unconsciousness reported in any animal is 3 seconds, with the longest periods well in excess of 60 seconds. The ranges in sheep are 5 to 22 seconds (most sheep 5-7 seconds), in goats are 3 to 7 seconds, and in cattle are 5 to more than 60 seconds. These variations are most likely due to the variable extent that the vertebral arteries maintain a sufficient blood supply to the brain bypassing the severed blood vessels of the neck cut. Ideally animals should not be shackled or hoisted before the onset of irreversible insensibility due to blood loss. Neither should any dressing procedure be performed before irreversible insensibility is established beyond doubt (Meat Standards Australia Committee 01/2004). The timing for these procedures should be established by checking each animal individually for any signs of sensibility rather than by observing a set time frame. In the Australian Standard (AS 4696:2007) there is a provision for ritual slaughter without prior stunning. 
This provision prescribes: An animal that is stuck without first being stunned and is not rendered unconscious as part of its ritual slaughter is stunned without delayafter it is stuck to ensure that it is rendered unconscious. 
The current state of scientific research on the topics of pain and distress suffered during the act of slaughter and the technologies available to alleviate such suffering overwhelmingly supports the use of pre-slaughter stunning.