Relationship between captive bolt placement, tissue parameters, and brain contact in cadaver heads from culled Holstein cows >30 mo of age

Penetrating captive bolt (PCB) is a method of euthanasia and preslaughter stunning for cattle. Industry guidelines include multiple PCB locations with minimal scientific justifications. Our objectives were to determine tissue depths, PCB position relative to anatomic features, and brain contact associated with 5 frontal placements and a poll placement for mature dairy cows. Cadaver heads were obtained from 22 Holstein cows >30 mo of age (hot carcass weight, mean ± SD: 278.83 ± 46.61 kg); all heads were stunned at a frontal location with a PCB at the collaborating slaughter establishment. Heads were cooled at 2°C to 4°C for ∼114 h before data collection. The frontal A placement was at the intersection of 2 lines from the lateral canthus of each eye to the center of the base of the opposite horn, or the equivalent position in polled animals. The frontal B placement was halfway between a line connecting the lateral canthus and top of the poll on the midline. The frontal C placement was 2.5 cm antirostral to frontal A. The frontal D placement was 5 cm antirostral to frontal A. The ideal frontal placement was based on the location of the thalamus. The poll placement was located just ventral to the external occipital protuberance at midline and directed toward the bottom of the central incisors. frontal A was marked on each head and a free-flight inline PCB was applied to each head at the poll placement. Tissue depth measurements were taken at these placements with a digital caliper. Tissue depth measurements were recorded at the remaining PCB placements from images collected during head processing. Mean separation was determined via Student's t-tests with the Bonferroni-Holm adjustment. Total tissue thickness was greater at frontal D (142.60 ± 2.26 mm; upper reference limit [URL]: 185.86 mm) and poll (36.81 ± 1.80 mm; URL: 47.15 mm), compared with frontal A (26.12 ± 1.80 mm; URL: 36.08 mm), frontal B (27.24 ± 1.80 mm; URL: 40.18 mm), frontal C (36.42 ± 1.80 mm; URL: 51.19 mm), and ideal frontal (27.53 ± 2.11 mm; URL: 38.50 mm). Thalamic depth was greater at poll (97.93 ± 1.73 mm; URL: 116.05 mm) than ideal frontal (84.82 ± 1.73 mm; URL: 96.31). The bolt path was located within the plane of the brain for all heads at frontal A, frontal B, frontal C, frontal D, ideal frontal, and poll; however, the bolt path was only located within the plane of the brain for 12/22 heads at frontal D. The bolt path was located within the plane of the thalamus for all heads at ideal, 15/16 heads for frontal A, and 10/16 heads for poll. The bolt path was not located within the plane of the thalamus for any heads at frontal B, frontal C, and frontal D. Of the placements evaluated in this study, ideal frontal appeared the most favorable for PCB use for Holstein cows >30 mo of age. Ultimately, ideal frontal, located ∼1 cm rostral to the intersection of 2 lines between the lateral canthus and the opposite outer lateral aspect of the poll, may present the least risk for failure of PCB euthanasia and stunning for Holstein cows >30 mo of age.