Evaluating the efficacy and safety of differing gun caliber and ammunition combinations for the euthanasia or depopulation of market-weight pigs

Objective: Evaluate the effectiveness and safety of firearm caliber and ammunition combinations that could be used on farm for euthanasia of market-weight pigs. Materials and methods: Heads from 64 market-age pigs (32 barrows and 32 gilts) were collected from a federally inspected slaughter facility. Heads were randomly assigned to one of 4 caliber and ammunition combinations: .22 long rifle (LR), .22 Magnum (Mag), .38 Special, and 9 mm. The fully jacketed ammunition was discharged from each of the 4 unique firearms (each with a 16-in barrel length) while ensuring a consistent muzzle to forehead distance of 12.7 cm. Results: The 9 mm bullets traveled further through the head and into the ballistic gel (P < .001) and the furthest total distance (P < .001). Bullets from the .38 Special traveled further into the ballistic gel and a further total distance than both the .22 LR and .22 Mag (P < .001). The trauma area of the brain was greater for the 9 mm and the .38 Special bullets when compared to .22 LR or .22 Mag, respectively (P < .001). There was no difference in the trauma area of the brain for the .22 LR bullets compared to .22 Mag bullets (P = .12). Implications: This proof-of-concept study generated data to define efficacy and safety considerations when using a firearm to euthanize market-weight pigs and demonstrated that the .22 LR full metal jacket bullet could provide predictable euthanasia in market-weight pigs with minimal risk of contralateral emergence.