Welfare of Pigs During Transport and Slaughter

Abstract

Humane slaughter, method of inducing death in animals without causing avoidable anxiety, fear, pain, suffering or distress, regulations require that stunning methods should induce immediate loss of consciousness. If the stun is not immediate, the induction of unconsciousness should occur without causing the animal avoidable fear, pain, anxiety, suffering or distress. The duration of unconsciousness must be longer than the sum of time that it takes to perform shackling and bleeding and the time to onset of death through blood lose at slaughter. Head-only electrical stunning is universally practised to stun pigs under commercial conditions, where high throughput rates are required. Electrical stun/kill is also performed by either passing an electric current from head-to-body using a single current cycle or by applying a current across the chest of head-only electrically stunned pigs (within 15s from the end of stun) to induce cardiac ventricular fibrillation using two separate current cycles. A minimum current of 1.3A delivered using 50 to 1500 Hz current will be necessary to induce satisfactory stunning and the same current level could also be applied using a 50 Hz AC to achieve stun/kill in single and two current cycle methods. Carbon dioxide stunning of pigs is becoming common however this method remains to be controversial on animal welfare grounds. This is because inhalation of high concentrations of carbon dioxide (40% or more in air) is extremely aversive to pigs and induces severe respiratory distress prior to the onset of unconsciousness. It has been recommended in the UK that carbon dioxide stunning of pigs must be phased out over the next five years. Alternatively, argon or nitrogen-induced anoxia (< 2% residual oxygen) is reported to be the pleasant way of loosing consciousness in humans and, certainly, pigs do not seem to find it aversive and they show no signs of distress during the induction of unconsciousness. Captive bolt stunning is the only stunning method available in some developing countries and is also used as a back-up method to stun pigs showing signs of return of consciousness in high throughput abattoirs. © Wageningen Academic Publishers, The Netherlands 2008.