Efficacy of a novel cervical dislocation tool for humane euthanasia of broilers and broiler breeders

Abstract

Euthanasia is an essential task performed daily on commercial poultry farms around the world to safeguard animal welfare. Manual cervical dislocation (MCD) is the most common euthanasia method but can be challenging to perform given the physical strength required to implement this technique. Therefore, the objective of this study was to evaluate the efficacy of a novel cervical dislocation tool (NCDT) compared to MCD. A total of 60 Ross 308 chickens (6-wk old) and 60 Ross 706 parent stock breeders (21-wk old) were enrolled in the study. Birds were sexed, blocked by body weight, and allocated to 1 of 2 treatments: 1) MCD and 2) NCDT. Immediately following euthanasia application, insensibility, and death were monitored. Once death was confirmed, gross evaluation, radiograph, and macroscopic/microscopic scoring were performed. Both euthanasia methods were 100% effective in achieving insensibility followed by cardiac and respiratory arrest in both age groups. In 6-wk-old broilers, there were no differences in insensibility measures or location and severity of the dislocation site by treatment. The NCDT treatment group showed an increased frequency of fractures located at the tooth-like process that projects from the cranial aspect of the centrum of the axis (dens) but had no impact on bird insensibility. For parent stock, differences in nictitating membrane reflex (NMR) and laceration scores for birds euthanized with NCDT were found and likely associated with additional force exerted with the tool. The NCDT is a promising replacement for MCD and future work should address the development of free and accessible training materials for on-farm use.

Keywords: animal welfare; broiler; broiler breeder; cervical dislocation; euthanasia.

Figure 1

Novel cervical dislocation tool in use.

Figure 2

Boxplot of time to cessation of nictitating membrane reflex (s) for 6-wk-old broilers and 21-wk-old broiler breeders (the diamond indicates the mean; the black circle indicates the outlier; and * indicates a significant difference).

Figure 3

Bar plot of dens fractures (presence or absence) for 6-wk-old broilers and 21-wk-old broiler breeders (* indicates a significant difference).

Figure 4

Lateral radiographs of a chicken with (A) and without (B) den fractures. In the chicken with the dens fracture, the dens (arrow) is superimposed with C1 and not seen on the cranial margin of C2 (closed arrow). In comparison, in the chicken without a fracture, the dens (open arrowhead) is seen on C2.

Figure 5

Boxplot of laceration scores between the treatments for 6-wk-old broilers and 21-wk-old broiler breeders (the diamond indicates the mean; the black circle indicates the outlier; and * indicates a significant difference).

Figure 6

Macroscopic findings in the 6-wk-old chicken groups. (A and B) From left to right are progressive rostral to caudal transversal dissections of the same bird head. (A) No macroscopic evident subdural hematomas (score = 0). (B) The subdural hematoma reaches the rostro-ventral area of the cranium (red arrows) (score = 2). (C and D) Longitudinal sections of the aboral cranium and occiput. All sections present subdural hematomas encircling the cerebellum and medulla oblungata. (C) The occipital condyle was intact (red asterisk) and articulating with a fractured first vertebral articular process (white asterisk). (D) The occipital condyle was intact (red asterisk) and articulating with an intact first vertebral articular process (white asterisk). (E) The occipital condyle was fractured (red asterisk). The gross panel was assembled in Biorender.com (Agreement number: IE25TWJU2N).

Figure 7

Microscopic observations in the 6-wk-old group. (A and B) Longitudinal sections of the dislocated end of the spinal column with spinal cord. (A) The articular surface of the vertebra was intact (black arrowhead, score = 0), subdural, subarachnoid, and parenchymal hemorrhages were moderate (back asterisk, score = 2). Spinal cord (Sc) was rarefied and fragmented near the site of dislocation. (B) Multiple fractures were effacing the vertebral edges (black arrowhead, score = 3), severe hemorrhage effaces meningeal compartment, and spinal canal (black asterisks, score = 3). The spinal cord (Sc) was fragmented and retracted into the canal. (C and D). Transversal sections of spinal column at 0.5 cm from the dislocated edge. (C) Mild subdural hemorrhage was present (black asterisk, score = 1). The spinal cord was mildly rarefied (score =1). (D) Presence of severe subdural and subarachnoidal hemorrhage (score = 3) which extends to the adjacent connective tissue. These were accompanied by moderate demyelination and rarefaction of the spinal cord. All scale bars (right bottom corner) are 500 um. Histopathological samples were assembled in Adobe Acrobat.