Electric Stunning

Taken from:Survey of Stunning and Handling in Federally Inspected Beef, Veal, Pork, and Sheep Slaughter Plants

Agricultural Research Service/United States Department of Agriculture - 3602-20-00 Project Number -3602-32000-002-08G

Temple Grandin, Ph.D.
Grandin Livestock Handling Systems, Inc.
2918 Silver Plume Dr., Unit C3
Fort Collins, Colorado 80526
USA January 7, 1997

Scientific research has shown that an electric stunner must have sufficient amperage to induce a grand mal seizure to insure that the animal will be made instantly insensible. For market weight pigs a minimum of 1.25 amps is required (Hoenderken 1982, Gregory 1988). For sheep a minimum of 1 amp is required (Gregory and Wotton 1984, Gilbert et al 1991). These amperages must be maintained for one second to induce instant insensibility. Insufficient amperage can cause an animal to be paralyzed without losing sensibility. The Council of Europe (1991) recommends the above minimum amperages. To insure sufficient voltage to deliver the amperage, 250 volts is the recommended voltage for pigs to insure insensibility (Troeger and Woltersdorf 1989). Research has also shown that too high of an electrical frequency will fail to induce insensibility. Warrington (1974) found that insensibility was most effectively induced at frequencies of 50 cycles. Frequencies at 2000 to 3000 hz failed to induce instant insensibility and may cause pain (Croft 1952, Van der Wal 1978). However, in pigs weighing under 200 lbs (80 kg) Anil and McKinstry (1994) found that high frequency1592 hz sinewave or 1642 hz square wave head only stunning at 800 ma (0.80 am p) would induce seizure activity and insensibility in small pigs. One disadvantage is that the pigs regained sensibility more quickly compared to stunning at 50 to 60 cycles. The pigs in this experiment weighed one third less than comparable U.S. market pigs and this probably explains why the lower amperages were effective. Some plants stun animals below the Council of Europe recommended minimum amperages in an attempt to reduce blood spots in the meat. Stunning market weight pigs with less than 1.25 amps should not be permitted (Grandin 1994a) unless different electrical parameters are verified by either electrical or neurotransmitter recordings from the brain. Since only a one second application at 1.25 amps is required to induce instant insensibility in market weight pigs, it is the author's opinion that plants should be permitted to use circuits which lower the amperage settings after an initial stun at 1.25 amps for pigs and 1 amp for sheep. Plants should also be encouraged to use electronic constant amperage circuits which prevent amperage spiking. Both practical experience and research has shown that these types of circuits greatly reduce petechial hemorrhages (Grandin 1985, Blackmore and Peterson 1981). Since U.S. market pigs are slaughtered at heavier weights compared to European pigs an electric stunner must deliver the minimum amperage recommended by the Council of Europe (1991) in order to be rated as either excellent or acceptable. It is the author's opinion that high frequency stunning should not be permitted in the U.S. until research is conducted to prove that it is capable of inducing an instantaneous grand mal seizure in heavier U.S. market weight pigs. In the Anil and McKinstry (1994) experiment, the pigs were stunned with a head only applicator. High frequency stunning has never been verified to induce instant insensibility when applied with a head to body cardiac arrest stunning electrode. This is the type of electrode used in almost all large U.S. pork slaughter plants. However, at the present time, pork plants should be permitted to use higher frequencies in their stunning cycle provided that the initial stun is a minimum of 1.25 amps at 50 to 60 hz for a minimum of one second.