Tool-based euthanasia methods for broiler chicks: Evaluating welfare outcomes of Iris and Kelly scissors

The most common euthanasia method for poultry is manual cervical dislocation (CD), but it is challenging to consistently perform in young chicks due to their small body size. Tool-assisted CD may offer an alternative. Our objective was to evaluate the efficacy of two tool-assisted CD methods with Iris (ICD) and Kelly (KCD) scissors compared to manual CD in 1-day-old (1DOA) and 7-day-old (7DOA) broiler chicks. Chicks were randomly and equally allocated to one of three euthanasia treatments: CD (n=20 1DOA, n=20 7DOA), ICD (n=20 1DOA, n=20 7DOA), and KCD (n=20 1DOA, n=20 7DOA). All euthanasia methods effectively rendered chicks insensible, followed by respiratory and cardiac arrest on the first attempt, with cardiac cessation occurring within 52 to 253 sec. Chicks euthanized with CD achieved cardiac arrest sooner at both ages (p=0.0154), displayed less mouth gaping at both ages (p=0.0006), lost the pupillary light reflex faster at 1DOA (p=0.0177), and displayed shorter clonic convulsions (p=0.0331) and feather erection (p=0.0538) at 7DOA compared to chicks euthanized with ICD and KCD. However, CD also displayed the highest macroscopic laceration score (p<0.0001) and subcutaneous hemorrhaging (p<0.0001) than KCD and ICD, and CD was the only method to result in decapitation. The ICD method achieved a similar consistency as CD in the site of vertebral separation, with the majority of separations occurring between C1-C2 vertebrae for both methods (p=0.0046). The KCD method resulted in lower separations (C2-C3 vertebrae; p<0.0001) and a higher incidence of vertebral and crushed fractures than CD and ICD (p=0.0303). Taken together, although all methods were successful in rendering chicks insensible, the CD resulted in insensibility metrics occurring sooner, particularly at 7DOA. However, the CD method demonstrated more lacerations and greater risk for decapitation, which may be more emotionally aversive to the person performing euthanasia. The ICD method offered an alternative to achieve similar consistency in cervical dislocation and brain trauma while minimizing macroscopic lesions and fractures.