Anatomical Pathology, Behavioral, and Physiological Responses Induced by Application of Non-penetrating Captive Bolt Devices in Layer Chickens

Abstract

We evaluated three models of non-penetrating captive bolt devices, Zephyr-E, Zephyr- EXL, and Turkey euthanasia device (TED) for time to loss of sensibility and degree of brain damage during euthanasia in four age groups of male and female layer chickens (10-11, 20-21, 30-35, 60-70 weeks respectively). Latencies to onset of insensibility and cardiac arrest were assessed to detect whether killing birds via these devices was humane and effective. Both gross and microscopic pathology evaluations were conducted to score skull and brain trauma post mortem. All three NPCB devices induced loss of breathing, pupillary reflex and nictitating membrane reflex within 5 s after application in most chickens. Latencies to loss of jaw tone and neck muscle tone were longer in 60-70 weeks old roosters (p < 0.05). Younger birds (10-21 week-old) demonstrated the longest time (p < 0.0001) to onset of tonic convulsions, time at last movement, cloacal relaxation and cessation of heart beat. A positive correlation (p < 0.0001) was found for all three devices between time of cardiac arrest and times to onset of tonic convulsions, last movement, and cloacal relaxation. More than 80% of birds had skin lacerations with external bleeding following application of all 3 devices. Device type did not affect the incidence of skull fractures but higher skull fracture scores were noted in 10-11 week-old birds compared to other ages. Regardless of device type and age, microscopic SDH was most apparent in the brain and proximal spinal cord of all birds. In summary, all three devices caused significant trauma to the midbrain and spinal cord. Results demonstrated that all three devices induce rapid insensibility after application and can be used as a single-step method that results in a humane death in all age groups of layer chickens.

Keywords: brain death; brain hemorrhage; brain stem reflexes; cardiac arrest; euthanasia; insensibility; poultry welfare.

Figure 1

Non-penetrating captive bolt devices. (A) Zephyr-E standard: (B) Conical shape bolt head, (C) Standard subject adapter. (D) Zephyr-E-layer: (E) Round shape bolt head, (F) Chicken subject adapter. (G) Zephyr-EXL: (H) Conical shape bolt head, (I) chicken subject adapter. (J) Turkey Euthanasia Device (TED): (K) Flat bolt head, (L) R-3 subject adapter.

Figure 2

Application of the Zephyr-EXL device on a 30 w.o. hen: The bird was restrained in sternal recumbency with its neck resting ventrally on the ground, and the wings held gently toward the body during the application of the device. Device was placed perpendicular to the top of the frontal bone just behind the comb and on the mid line between the eyes and ears.

Figure 3

Gross pathology scoring criteria for skull fractures. Arrows indicate the fracture type [modified from Erasmus et al. (12) and Casey-Trott et al. (15)]. (A) No fracture, intact skull (score 0). (B) Depression fracture (score 1). (C) Penetrating fracture-no imbedded fragments (score 2). (D) Penetrating fracture- with imbedded fragments (score 3).

Figure 4

Skin reflected to demonstrate gross subcutaneous hemorrhage. (A) Hemorrhage with less than 25% of area covered (score 2) of a 65 w.o. bird killed by the TED. (B) Hemorrhage completely covering area from the eyes to base of the skull (score 4) of a 10 w.o. bird killed by the TED. (C) Gross subdural dorsal hemorrhage covering <25% of the brain surface (score 1) of a 33 w.o. bird killed by the Zephyr-E. (D) Gross subdural dorsal hemorrhage covering 51–75% of the brain surface (score 3) of a 33 w.o. bird killed by the Zephyr-E.