Validating the effectiveness of alternative euthanasia techniques using penetrating captive bolt guns in mature swine (Sus scrofa domesticus)

Abstract

Euthanasia of mature swine is challenging. Temporal and behind-the-ear locations are two sites that have been identified as alternatives to the more commonly used frontal placement. In stage-one, the effectiveness of two penetrating captive bolt gun styles (cylinder or pistol) was evaluated using frontal, temporal and behind-the-ear placement in anesthetized mature swine (n=36; weight: 267 ± 41 kg). For stage-one, when evaluating treatment efficacy by sex, the cylinder style equipment was 100% effective in achieving death when applied to all cranial locations (frontal, temporal, behind-the-ear) for sows; however, the pistol style equipment was only 100% effective when applied at the behind-the-ear location for sows. For boars, the cylinder style equipment was 100% effective when applied to the frontal and behind-the-ear location, but the pistol style equipment was not effective for any cranial location in boars. Therefore, the pistol-frontal, pistol-temporal, pistol- behind-the-ear and cylinder-temporal were not included for boars, and pistol-frontal and pistol-temporal were not included for sows in stage-two. In stage-two, commercial, mixed breed, mature swine (n=42; weight: 292 +/- 56 kg) were randomly assigned to one of four treatments based on inclusion criteria described in stage-one. A 3-point traumatic brain injury (TBI) score (0=normal; 1=some abnormalities; 3=grossly abnormal, unrecognizable) was used to evaluate six neuroanatomical structures (cerebral cortex, cerebellum, hypothalamus, thalamus, pons and brain stem) and the presence of hemorrhage was also noted. All treatments were 100% effective in stage-two. A significant interaction between gun style and placement was determined on predicting total TBI as the cylinder style produced a higher total TBI score compared to the pistol type, of magnitude of +2.8 (P < 0.01). The cylinder style tended to produce a greater TBI score than the pistol in the temporal location (+1.2; P=0.08). No difference was noted for TBI score behind-the-ear between the cylinder and pistol style gun (P>0.05). TBI tended to be less in boars compared to sows (-0.6; P=0.08). Hemorrhage was observed in frontal, parietal, occipital and temporal lobes. This study demonstrated that the cylinder style captive bolt gun more effectively resulted in brain trauma and death compared to a pistol style gun and the behind-the-ear and temporal placement showed promise as an alternative placement site for euthanizing mature pigs on-farm.

History and best practices of captive bolt euthanasia for swine

“…The majority of peer-reviewed scientific publications on the topic at the time of this review were focused on NPCB euthanasia of neonatal (3 d of age or younger) pigs ( Casey-Trott et al, 2013 , 2014 ; Grist et al, 2017 , 2018a , 2018b ). At the time of this review, one peer-reviewed scientific publication exists related to the PCB euthanasia of grower-finisher swine ( Anderson et al, 2019 ) and two on the PCB euthanasia of breeding swine ( Anderson et al, 2021 ; Kramer et al, 2021 ). In addition, a thesis focuses on the NPCB and PCB euthanasia of six weight classes of swine, from 2 to 200 + kg ( Woods, 2012 ).…”

“… Woods (2012) and Kramer et al (2021) both evaluated the efficacy of euthanasia with PCB devices for breeding swine. In contrast with the Anderson et al (2021) study, each of these studies was able to assess efficacy because live animals were used.…”

“…It is unclear if an immediate second shot would have been required for two animals where respiration post-application was observed but no eyeblink response was reported ( Woods, 2012 ). Kramer et al (2021) focused on the efficacy of euthanasia with two PCB types (pistol and inline) at the temporal and behind ear placements for live, mature swine. Similar to the Woods (2012) study, this was performed in two stages: first on anesthetized animals and then on live-conscious animals.…”

“…In the first stage, death was achieved within 10 min of PCB application for three of three anesthetized sows with the inline-frontal, inline-temporal, inline-behind ear, and pistol-behind ear device-placement combinations; at least one of the three animals was not effectively euthanized with the pistol-frontal and pistol-temporal device-placement combinations ( Kramer et al, 2021 ). Effective euthanasia with death occurring within 10 min of the PCB application occurred for three of three anesthetized boars with the inline-frontal and inline-behind ear device-placement combinations; at least one of three boars did not achieve death following a PCB application with the following device-placement combinations: inline-temporal, pistol-frontal, pistol-temporal, and pistol-behind ear ( Kramer et al, 2021 ). The findings of Woods (2012) and Kramer et al (2021) indicate that the pistol-type PCB applied in the frontal placement may not be an effective means of euthanasia for mature breeding swine.…”

“…Effective euthanasia with death occurring within 10 min of the PCB application occurred for three of three anesthetized boars with the inline-frontal and inline-behind ear device-placement combinations; at least one of three boars did not achieve death following a PCB application with the following device-placement combinations: inline-temporal, pistol-frontal, pistol-temporal, and pistol-behind ear ( Kramer et al, 2021 ). The findings of Woods (2012) and Kramer et al (2021) indicate that the pistol-type PCB applied in the frontal placement may not be an effective means of euthanasia for mature breeding swine.…”