Technical Note: Validation of the effectiveness of electric stunning for euthanasia of mature swine (Sus scrofa domesticus)

Lay Summary Euthanasia is a moral obligation of all individuals working in the swine industry. A majority of acceptable methods have been validated for market weight pigs, while less attention has focused on heavy-weight mature boars and sows. The objectives of the current study were to evaluate the effectiveness of a mobile electric stunner (E-STUN) as a method of humane euthanasia in heavy-weight mature boars and sows and to assess the outcomes when compared with a penetrating captive bolt gun (PCBG) method. The efficacy of the treatment was defined as any pig that achieved cardiac and respiratory arrest within 10 min after treatment application. The amount of traumatic brain injury was evaluated across the brain, and the presence of intracranial hemorrhage was also noted. All animals were immediately rendered insensible, and rhythmic breathing was absent following either treatment application. Boars and sows had a decreased time to last heartbeat with the E-STUN when compared with the PCBG method. Intracranial hemorrhage was common for both methods, and visible disruption of brain tissue was evident due to the physical nature of the PCBG. This study demonstrated that a mobile E-STUN is as effective as a PCBG for humane euthanasia of heavy-weight mature swine. A limited number of safe and reliable euthanasia methods have been documented and validated for mature boars and sows. This study evaluates the efficacy of a mobile electrical stunning device as a method of euthanasia for heavy-weight mature boars and sows. Electrocution and the use of a penetrating captive bolt gun (PCBG) are both acceptable methods of euthanasia for market weight swine. Research has demonstrated that a PCBG is effective in both growing and mature swine. Given limited to no published research base on electrocution in mature swine, the objectives of the present study were to evaluate the efficacy of a two-stage (head only followed by head to heart, 10 s contact for each) mobile electric stunner (E-STUN, Hubert HAAS TBG 96N) and to assess euthanasia outcomes when comparing E-STUN with the frontal placement of a heavy-duty PCBG (Jarvis, In-line Cylinder Style) when applied to heavy-weight (>200 kg) mature boars and sows. Effectiveness of the E-STUN and PCBG was evaluated first in unconscious anesthetized mature swine (n = 7 boars and sows per treatment; average weight 282 +/- 48 kg, n = 28) to reduce the risk of failure in a conscious animal and then in conscious mature swine (n = 3 boars and sows per treatment; average weight 282 +/- 63 kg, n = 12). Data from both stages were combined for analyses. Treatment efficacy was defined as any pig that achieved cardiac and respiratory arrest within 10 min after treatment application. A three-point traumatic brain injury score (0 = normal; 1 = some abnormalities; and 2 = grossly abnormal, unrecognizable) was used to evaluate six neuroanatomical structures (cerebral cortex, cerebellum, hypothalamus, thalamus, pons, and brain stem), and the presence of intracranial hemorrhage was also noted. All animals were immediately rendered insensible with E-STUN and PCBG, and no difference was noted between treatments for the detection of corneal reflex following treatment application (P = 0.11). Rhythmic breathing was absent following the administration of either E-STUN or PCBG. When evaluating the time to last heartbeat, there was a significant interaction between sex and treatment. Boars euthanized via E-STUN had a 346.8-s decrease in time to last heartbeat compared with boars euthanized via PCBG (P < 0.001), and females euthanized via E-STUN had a 479.3-s decrease in time to last heartbeat compared with females euthanized via PCBG (P < 0.001). Intracranial hemorrhage was common for both methods, and visible disruption of neural tissue was evident due to the physical nature of the PCBG. This study demonstrated that a mobile E-STUN system is as effective as a heavy-duty PCBG in inducing insensibility and death and shows promise as an alternative method for euthanizing mature pigs on-farm.