Assessment of Methods for On-Farm Euthanasia of Layer Chickens
Animal care guidelines for poultry require that the methods used for routine killing result in rapid and irreversible loss of sensibility and cause minimal pain and distress. This thesis assessed the efficacy of three types of physical on-farm euthanasia methods in different age groups of layer chickens, and the degree of aversion and time to loss of sensibility for different CO2 concentrations (25%, 35%, 50%, and 70%) in laying hens. In Study 1, all three commercially available non-penetrating captive bolt devices tested caused sufficient brain trauma to result in rapid insensibility and brain death in four different age groups (10-11, 20-21, 30-35, 60-70 weeks) of layer chickens. This study also identified and corroborated practical behavioural indicators of death in layer chickens that can be used in field conditions to achieve the animal care guideline requirements of confirming the death before disposing of carcasses; onset of tonic convulsions, last movement, and cloacal relaxation were good indicators of clinical death. A second study assessed efficacy of a commercially available mechanical cervical dislocation device (MCD) in comparison to manual cervical dislocation (CD) in different age groups (12, 27-29, and 65-70 weeks) of layer chickens. Killing methods were assessed in anesthetized chickens to minimize welfare concerns. MCD resulted in a longer time to brain death than CD. Radiographs revealed that the majority of birds killed by CD had ideal dislocation sites between the skull and atlas (C1) or between cervical vertebrae C1-C2. The MCD resulted in a majority of dislocations at lower cervical vertebrae. There were few fractures in birds killed by either method. A final study demonstrated that concentrations of 50% and 70% CO2 were significantly more aversive to laying hens than 25% and 35%, based on an approach avoidance test. However, hens demonstrated headshaking and open mouth breathing at all tested CO2 concentrations, and some birds displayed conditioned place avoidance at the low concentrations. Loss of posture, indicating insensibility, occurred in less than 25s in all CO2 concentrations with shorter latencies at higher concentrations. The thesis provides important information for refinement of future euthanasia guidelines for the layer chicken industry.