In the event of an infectious animal disease outbreak, rapid depopulation of the infected livestock herds can help prevent the spread of the disease and potentially reduce suffering of the impacted animals. There are several options for rapid depopulation; however, many methods require substantial labor inputs or specialized equipment, both of which may be difficult and expensive to procure. Delays in depopulation prolong the infection, spread of the disease, and suffering of the affected animal. Inhaled gases for depopulation are advantageous because moderate to low skill is required, can be aesthetically preferable, with only some excitatory movement or vocalization, and can be used on any size pig. Carbon dioxide (CO2) is the most common gas used, but carbon monoxide (CO) could become a viable alternative to CO2. This project aimed to explore the feasibility of using CO as inhalant at full-scale. The first step was to create computational fluid dynamics (CFD) simulation to investigate the transport of CO in a 28 ft wide, 120 ft long, and 7.5 ft tall with a 3 ft deep-pit nursery. Initial modeling with only one CO inlet into the barn showed the desired CO concentration of 4,000 ppm was quite unachievable, especially if any building envelope leakage or strong wind was present. Then, the simulation was
adapted for three CO inlets and results showed more uniform distribution of CO within the pig occupied space; however, concentration of CO failed to achieve the desired 4,000 ppm within 30 minutes. Implementation of CO at full-scale unachievable with the following conclusions: compressed, pure CO procured from an industrial gas supplier, as compared to on-site CO generation, is a more viable option for depopulation when considering cost, safety, availability of application equipment and system reliability. Currently sales of inert gases, such as CO, “where the planned use is as an asphyxiant or toxin to be applied to animals is prohibited, without formal product risk review” by Linde Gas and Equipment, which is the primary supplier of compressed CO in the US. Linde will not move forward with their formal product risk review without justification of the market potential of CO for depopulation. For more information, please contact Dr. Brett Ramirez in the Department of Agricultural and Biosystems Engineering at Iowa State University; email: bramirez@iastate.edu

Key Findings
• A computer simulation using computational fluid dynamics was performed to explore the transport of CO throughout a small nursery building with one and three CO inlets. A simulation of this scale, in three dimensions, has never been created before and could be easily adjusted for different gases, injection locations, buildings, etc.
• One CO inlet showed the target CO concentration of 4,000 ppm was quite unachievable. Three CO inlets results showed more uniform distribution of CO within the pig occupied space; however, concentration of CO failed to achieve the desired 4,000 ppm within 30 minutes.
• Building envelope leakage (infiltration) due to poor/degraded construction or materials and/or wind have a substantial effect on the transport of CO within the room and should be strongly considered for any future discussion on full-scale usage of inhalants.
• Compressed, pure CO procured from an industrial gas supplier, as compared to on-site CO generation, is a more viable option for depopulation when considering cost, safety, availability of application equipment and system reliability.
• Currently sales of inert gases, such as CO, “where the planned use is as an asphyxiant or toxin to be applied to animals is prohibited, without formal product risk review” by Linde Gas and Equipment, which is the primary supplier of compressed CO in the US. Linde will not move forward with their formal product risk review without justification of the market potential of CO for depopulation.