Efficacy of three different cervical dislocation methods for on-farm killing of layer chicks

Unfit chicks with low viability are often euthanized in the layer industry. An effective euthanasia protocol is characterized by rapid, irreversible insensibility, followed by prompt death. This study was conducted to evaluate the efficacy of three cervical dislocation methods for killing layer chicks (2-3-day-old, avg BW ± SD; 44 ± 3 g, n = 40): manual cervical dislocation (CD), assisted manual cervical dislocation (ACD; the bird's ventral neck is placed on a blunt table edge and the back of the neck pressed firmly), and mechanical cervical dislocation by Koechner Euthanizing Device (KED-model-S). All three killing methods were assessed on anesthetized chicks (intramuscular injections of medetomidine [0.3 mg/kg BW] and ketamine [30 mg/kg BW] were used to induce clinical anesthesia). CD and ACD were also evaluated using conscious chicks to compare the killing methods and to determine the effect of anesthesia on response variables. There were no differences in time to loss of pupillary light reflex, cessation of heartbeat, or duration of gasping between conscious chicks killed with CD and ACD, but these values were all longer for conscious compared to anesthetized chicks. KED resulted in longer latencies to loss of pupillary light reflex, cessation of heartbeat, and duration of gasping. Radiographs revealed that both CD and ACD resulted in cervical luxation, mainly below the C4 vertebra, whereas KED did not cause luxation in any of the 8 chicks tested. Chicks killed by CD and ACD presented more subdural hemorrhage (SDH) at the site of cervical dislocation than those killed by KED. None of the killing methods resulted in brain trauma. Compared to CD and ACD, KED resulted in longer latency to brain death and less anatomical pathology indicating a lower efficacy of KED as an on-farm killing method.