The American Veterinary Medical Association (AVMA) defines depopulation as “the rapid destruction of a population of animals in response to urgent circumstances with as much consideration given to the welfare of the animals as practicable”.1 There is a multitude of causes that necessitate the depopulation of swine. These causes include an animal health emergency, natural disaster, animal welfare emergency, and industry disruption. The AVMA categorizes methods of depopulation as approved, permitted in constrained circumstances, and not recommended. For swine, the approved methods include gun shot, penetrating captive bolt, non-penetrating captive bolt, blunt force trauma (size dependent), electrocution, injectable anesthetic overdose, and inhalant gases. The permitted in constrained circumstances include ventilation shut down plus and sodium nitrite.1
The U.S. pork industry has continued to prepare for the introduction of a foreign animal disease (FAD), like African Swine Fever Virus (ASFV) which has recently been detected in the western hemisphere. Ongoing industry simulations of a FAD outbreak and the depopulations incurred in 2020 due to the Corona Virus Pandemic (Covid-19) have reaffirmed our lack of resources and infrastructure necessary to conduct large-scale mass depopulation of swine in the U.S.2
The swine industry must continue to research and evaluate efficiently scalable methods of depopulation, providing a rapid loss of consciousness, and minimizing anxiety, pain, and distress of the animals. Further, these methods should consider the mental welfare and physical requirements of the caretakers performing these depopulations across the broad range of sizes of swine in our industry.
Nitrogen gas (N2), as an approved method for euthanasia of swine, has not traditionally been used for gassing in open spaces or containers because of the practical difficulty to displace the oxygen to adequately low enough levels (<2%).3 Livetec Systems has developed a Nitrogen Foam Delivery System (NFDS) that allows for the delivery of an inert gas (nitrogen) within a high expansion foam that envelopes the animal thereby displacing oxygen levels and resulting in death by anoxia. The objectives of this study were to validate the use of high expansion nitrogen foam technology for the large-scale depopulation of swine and demonstrate the Livetec Systems Nitrogen Foam Delivery System (NFDS) for the large-scale depopulation of swine across multiple classes of swine to producers, veterinarians, researchers, and regulatory officials.
A 40 cubic yards roll-off dumpster and a portable cattle corral gating system were used for animal containment. The dimensions of the corral system were set to match that of the roll-off dumpster’s internal measurements of 21′ L x 7′ W x 7′ H. Further, the corral gating had ¼ inch plywood placed from the ground to a height of 4′ and plastic bird netting extended to a height of 7′ to contain the foam. Nitrogen gas was provided to the NFDS by a nitrogen pumper tanker and vaporizer; the gas was provided at a flowrate of 100,000 – 110,000 standard cubic ft/hour and a temperature of 70 – 80 F. The NFDS system then mixed this gas with water and a Class B high expansion (fluorine-free) foam concentrate with the goal to produce a 20 mm bubble through a single foam generator at a rate of 1600 cu ft / min. All replicates had foam filled to a height of 7 ft to evaluate the fill time of a standard volume container. Filling a container to a height of at least two times that of the height of the animals being depopulated would be the recommended fill height. Once the container was filled, the nitrogen system was shut off, and a 20-minute dwell time was observed to ensure a minimum 7-minute exposure period to the Nitrogen gas and ample dewatering of the foam prior to using air lances (leaf blowers) to remove the foam and evaluate the animals.3
There was continuous monitoring and video recording during each replicate of depopulation. Prior to the trial, three (3) animals per replicate were anesthetized and had monitoring devices surgically implanted subcutaneously over the xiphoid process (sternum). These devices monitored temperature, heart rate, and activity. Ten (10) animals had accelerometers placed on a hind limb per replicate to monitor activity. Animals were also observed for escape attempts, grunts, squeals, and time to cessation of movement (COM). Death was confirmed, by a veterinarian, at the time of carcass removal. Ten pigs per replicate were then necropsied to evaluate for the presence of foam and if a total occlusion of the trachea occurred.
Phase 1 of this study utilized two (2) sedated feeder pigs to evaluate the successful cessation of life at the end of the twenty (20) minute dwell time and lack of tracheal occlusion by the nitrogen foam. Phase 2 evaluated three replicates of feeder pigs utilizing 156 pigs averaging 73 lbs. The finishing pig replicate used 45 pigs averaging 240 lbs. The adult replicate utilized 25 animals averaging 390 lbs. The wean pig replicate utilized 325 pigs averaging 11.8 lbs. The adult and wean pig replicate also achieved the second objective. These were conducted with over 60 invited industry guests present to observe the depopulation. To reduce the time needed for observation, the wean pigs were contained within the corral system; this replicate was the only replicate to depopulate in the corral. All others utilized the 40 cubic yard roll-off container.
The time to fill the 40 cubic yard roll-off dumpster to 7 ft ranged from 100 to 140 seconds for complete container fills. The first two replicates of the phase 2 nursery evaluations utilized a divider wall to reduce the internal volume to one half the size. These two replicates took 80 and 89 seconds to fill. During the phase 2 observation of adult and wean pig groups, the wean pig group took 141 seconds to fill the corral, while the adult group took 100 seconds to fill the solid-sided roll-off container.
Evaluating the surgically implanted sensors, the average time to COM, from the start of foam filling, for the first two replicates of the nursery pigs were 100.3 and 89.0 seconds. The third replicate took 151.3 seconds, which was similar to the 44 to 54 seconds of additional fill time required to fill the container. For the market weight group, the average time to COM was 63.3 seconds. The adults took an average of 169.25 seconds to achieve COM.
There were 28 nursery pigs evaluated for the presence of foam in the trachea. A total of 13 animals had the presence of foam. Of the ten market animals evaluated, seven had the presence of foam. Six of the twelve adult animals evaluated had the presence of foam. The wean pigs had six of the ten pigs evaluated show the presence of foam. Of these 60 animals evaluated, none showed signs of occlusion of the trachea. Thus, presuming that death was achieved by anoxia from exposure to inert gas.
In summary, a total of 6 replicates utilizing a total of 551 pigs from wean age to adult were successfully depopulated using high-density expansion foam with the Livetec Nitrogen Foam Depopulation System. The Livetec Systems NFDS was demonstrated to over 60 pertinent industry representatives.
- High expansion water-based foam as a delivery system for Nitrogen gas (N2), an inert gas, successfully depopulated all classes of swine. No animals needed to be euthanized. (post 20-minute dwell time.)
- Although foam was present in some of the tracheas, there was no observed tracheal obstruction by the foam under the conditions of this study. Thus, presuming that death was achieved by anoxia from exposure to inert gas.
- As evaluated via the implanted sensor, the average time of COM, ranged from 63.33 to 169.25 seconds post start of foam filling, for feeder pig, market, and adult animals.
For further questions or information on this study, please contact:
Todd Williams, DVM