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accumulation of waste products. This causes brain dysfunction and brain death. Correct slaughter will lead to rapid effective blood loss. Consequently energy and oxygen supply progressively falls to the heart and brain and both will stop to function over time (Michiels, 2004; Rosen, 2004; Pallis, 1982a; Pallis, 1982b; Pallis, 1982c; Pallis, 1982d). 2.8
Physiology of exsanguination or bleeding out
Slaughter is the process of bleeding to induce death, usually by severing major blood vessels supplying oxygenated blood to the brain (see Dialrel glossary in the annex of this report and EFSA (2004)). After severing the major blood vessels of the neck, with either reversible or without stunning, animals die due to loss of circulating blood volume and the resultant cerebral anoxia. Exsanguination can be carried out either by neck cut or thoracic cut. A neck cut according to the Dialrel glossary, involves severing of major blood vessels in the ventral neck region (skin and vessels cut simultaneously). Neck cutting also referred to as throat cutting means an incision below the angle of the jaw. The two carotid arteries and jugular veins are severed simultaneously with the oesophagus trachea and vagus nerves. This practice has been suggested as not been optimal with regard to hygiene reasons. According to the EU hygiene regulations, “the trachea and oesophagus must remain intact during bleeding” (VO EG Nr 853/2004, Annex III, Sec I, Chap IV, No. 7. a3). Nevertheless the practise of severing the trachea and oesophagus is explicitly allowed in the EU hygiene regulations in the case of religious slaughter. The thoracic cut according to the Dialrel glossary is described as “severing major blood vessels emerging from the heart by inserting a knife in front of the brisket or sternum (double cut: first the skin, then, with another knife, the vessels)”. By thoracic or rather pre-thoracic cut of cattle (also imprecisely referred to as chest stick), the brachiocephalic trunk is severed immediately cranial to the thoracic inlet. The brachiocephalic trunk is a single large vessel that emerges from the aorta and gives rise to the common carotid arteries, which supply the head with blood. 2.8.1
Loss of blood volume, loss of blood pressure
The circulating blood volume in animals is estimated to be 8% of body weight and about 18% of total cardiac output flows through the brain at any one time (EFSA, 2004, page 23). With adequate incision of the neck vessels all animals loose between 40 and 60% of their total blood volume and the pattern and rate of loss is similar in the various species examined (Warriss and Wilkins, 1987). Cutting leads to a drop in blood pressure, which may result in hemodynamic instability, interruption of blood supply to the brain and other organs. This can result in insufficient perfusion of tissues with blood, leading to inadequate oxygenation and removal of toxic waste products. Life threatening drops in blood pressure are often associated with a state of shock – a condition in which tissue perfusion is not capable of sustaining aerobic metabolism. The bodies compensatory response to a hemorrhagic shock caused by bleeding, includes systemic reactions such as increased heart rate, local vasoconstriction of arterioles and muscular arteries and shifting of extravascular and venous reserve fluids to the circulating blood volume. This response aims to enhanced cardiac output and maintenance of perfusion pressure, especially in heart, brain and adrenal glands (Guiterrez et al., 2008). The time lag between severe haemorrhage and unconsciousness certainly depends on whether and how long compensatory mechanisms are successful or whether they are eventually overwhelmed by blood volume losses (Gregory, 2005a). 3
7. Stunning, bleeding, skinning, evisceration and other dressing must be carried out without undue delay and in a manner that avoids contaminating the meat. In particular: (a) the trachea and oesophagus must remain intact during bleeding, except in the case of slaughter according to a religious custom;