CO2 Euthanasia System with Improved Process Control
Project 18-005- Lead Resesarcher: John Van de Vegte, OMAFRA
Researchers: John Van de Vegte, OMAFRA; Summer Student- Keegan Cleghorn, University of Guelph, Engineering.
Project start: May 2018 Project Completion: September 2019
Carbon dioxide (CO2) gas is commonly used as gas in on-farm euthanasia systems. This method is intended to provide a low stress event for both the pigs and the stockpeople managing the process. The system is an alternative for those who do not feel comfortable with the use of a zephyr/captive bolt gun or blunt force for euthanasia and as such may play a small role in worker retention.
Commercially available CO2 euthanasia systems employ a process control method which simply opens and closes the CO2 supply valve according to preset time durations. However, there are inherent issues with the current commercial control methods which can be improved to make the system more humane and efficient.
Issue #1: Residual gas in the chamber: An effective and humane system brings the concentration of CO2 gas up slowly, so that the pigs are not stressed by the experience. CO2 gas is heavier than air. High concentrations of the CO2 gas will remain in the euthanasia chamber after a cycle is completed which will then cause immediate stress to the next group of pigs being placed in the chamber.
Issue #2: Limited Control: The existing system’s control method provides no ability to adjust the process based on the size and number of pigs in the euthanasia chamber for each cycle.
Issue #3: CO2 Concentration Optimization: CO2 gas concentration is not measured in euthanasia system currently available.
The objective of this project was to develop a prototype CO2 gas euthanasia system that incorporates improvements to the issues noted above in commercially available systems.
Methods and Results
The euthanasia chamber including all valves, piping, fans and circuitry are integrated into a single, wheel-mounted enclosure (Figure 1). The system touchscreen controller (Figure 2) provides the operator simple controls to choose 1 of 3 piglet sizes and the ability to start, pause or stop the process. System status and fault messages are also provided on the screen.
A pressure regulator is employed to reduce the CO2 gas supply tank down to the required 15 psi delivery pressure. The flow meter stabilizes the flow rate of CO2 gas into the chamber at required levels. Without the flow meter, CO2 gas flow rates would vary widely depending on the pressure in the supply tank. The use of the flow meter also provides for the elimination of the expensive gas heater unit required on commercial units.
Amongst all the euthanasia cycles monitored, the average time to loss of consciousness for the last pig in each euthanasia group amongst all the test cycles was 3.54 minutes. The average time to complete loss of motion was 8.17 minutes.
Variation in these time points were noted based on pig size and condition. Based on visual monitoring of each cycle, smaller pigs required longer exposure to the high CO2 gas concentration within the chamber to ensure euthanasia was achieved. There appear to be 2 key drivers for variation in time to unconscious and time to loss of motion.
1. Pig weight: Smaller pigs require more time in a high CO2 gas environment to achieve unconsciousness and loss of motion.
2. Pig condition: Weaker pigs require less time in a high CO2 gas environment to achieve unconsciousness and loss of motion.
The farm reported a cost of $80 for a 100lb cylinder of compressed carbon dioxide gas. This size of high pressure cylinder contains 873 cubic feet of gas. At an average consumption of 7.88 cu.ft. of CO2 gas per euthanasia cycle, one tank of gas would last for approximately 110 cycles. The CO2 gas cost per cycle would be $0.72. With an average gas consumption of 5.85 cu.ft per cycle, one tank of gas would last for approximately 149 cycle. The associated gas cost per cycle would be reduced to $0.54.
The integration of improved process control to the CO2 gas euthanasia process results in a stable, repeatable process to minimize stress on pigs and stockpeople. Real-time monitoring of CO2 gas concentrations combined with exhaust port and chamber ventilation control ensures that the CO2 gas profile within the chamber is optimized while avoiding aversion responses by the pigs.
Researcher Profile: John Van de Vegte, OMAFRA