Abattoir Practices and Animal Products Technology

Types of Gas Stunning Apparatus

TYPES OF GAS STUNNING

The type of apparatus employed to administer the gas depends mainly upon the required rate of slaughter.  There are three main forms:

• The oval tunnel (Combi) system
  • This is used for killing rates of up to 600 pigs per hour.
  • The gas tunnel is in the form of an oval through which a slot conveyor carries pigs, the actual tunnel sloping downward at an angle of 30˚ to the anaesthetizing chamber.
  • On exit the pigs are shackled, hoisted to an overhead rail and bled.
  • The actual conveyor in the tunnel is divided into ten compartments, one pig being accommodated in each compartment.
  • Pigs up to 113 kg can be handled in this equipment, which is not suitable for other species.
• The dip lift system
  • This is suitable for any size of pig as well as calves and sheep.
  • It consists of a cage 213 cm long, 68 cm high and 53 cm wide which, when the animal enters it, descends vertically to the CO₂ pit where it remains for the pre-set time and then automatically returns to ground level, ejecting the unconscious animal for shackling and bleeding.
  • The greatest advantage of the system is that it allows several pigs to be stunned simultaneously, assisting immediate per-slaughter handling.
  • This is suitable for small meat plants.
• The compact CO₂  immobiliser
  • This is a horizontally-revolving apparatus divided into four to eight compartments operating in such a way that, when one section is uppermost for loading, the others are rotating to submerge in the gas chamber.
  • The unit usually has a capacity of up to 300 pigs per hour.
  • In commonly used design the pigs are exposed to 10% CO₂ at the first position, 30% for 10s at the second, 60% for 10s at the third and over 90% for 20s at the fourth and fifth, after which the pigs are discharged from the unit.
  • Pigs go into the machine quietly, become unconscious and remain as far one to two minutes, allowing plenty of time for sticking, they bleed out well, heart action is strong and their is no spasm to delay for continuous flow of blood, very little distress.
  • Concentration of Carbon-di-oxide approximately 65% first 15 seconds apparently unaffected by Carbon di oxide.
  • 15 seconds later state of excitement when they bend their heads backwards and fall over on to their sides.
  • 5 seconds later the sense of pain seems to have been lost.

• CO₂ anaesthesia has been utilized for turkeys and domestic fowl, mostly on an experimental basis.
• A concentration of 73-77% CO₂ has been found to be most suitable for turkeys and 70% for chicken.
• Chickens lose consciousness in about 15 seconds and may retain it in 1.5 minutes; with an exposure of 1 minute unconsciousness may extend for 4 minutes.