Relationship of tissue dimensions and three captive bolt application sites on cadaver heads from mature swine (Sus scrofa domesticus) <200 kg body weight

Karly N Anderson; Ashlynn A Kirk; Jennifer Berger; Arquimides A Reyes; Ruth Woiwode; Perle E Zhitnitskiy; Kurt D Vogel

doi:10.1093/jas/skae045

. 2024 Feb 15;102:skae045. doi: 10.1093/jas/skae045

Relationship of tissue dimensions and three captive bolt application sites on cadaver heads from mature swine (Sus scrofa domesticus) <200 kg body weight

Karly N Anderson ¹, Ashlynn A Kirk ², Jennifer Berger ³, Arquimides A Reyes ⁴, Ruth Woiwode ⁵, Perle E Zhitnitskiy ⁶, Kurt D Vogel ^7,^✉

PMCID: PMC10941640 PMID: 38366605

Abstract

Penetrating captive bolt (PCB) is a common method of euthanasia for swine but has not been evaluated for mature swine < 200 kg body weight (BW). The objectives were to determine tissue depth, brain contact plane, and visible brain tissue damage (brain damage[BD]) for the common FRONTAL (F) and alternative TEMPORAL (T) and BEHIND EAR (BE) placements for PCB use on sows and boars weighing < 200 kg. Cadaver heads were obtained from 30 sows and 30 boars (estimated BW, mean ± SD; sows: 165.8 ± 22.4 kg; boars: 173.6 ± 21.4 kg) from a slaughter establishment after electrical stunning and exsanguination. Heads were cooled at 2 to 4 °C for approximately 64 h. A Jarvis PAS-Type P 0.25R PCB with a Long Stunning Rod Nosepiece Assembly and a 3.5 GR power load was used for all PCB applications at the following placements: F–3.5 cm superior to the optic orbits at midline, T–at the depression posterior to the lateral canthus of the eye within the plane between the lateral canthus and the base of the ear, or BE–directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye. For sows, the bolt path was in the brain for 10/10 (100.0%, 95% CI: 69.2% to 100.0%) F, T, and BE heads. In heads that could reliably be assessed for BD, BD was detected in 10/10 (100.0%, 95% CI: 69.2% to 100.0%) F heads, 9/9 (100.0%, 95% CI: 66.4% to 100.0%) T heads, and 0/10 (0.0%, 95% CI: 0.0% to 30.1%) BE heads. For boars, the bolt path was in the plane of the brain for 8/9 (88.9%, 95% CI: 51.8% to 99.7%) F heads, 9/10 (90.0%, 95% CI: 55.5% to 99.7%) T heads, and 11/11 (100.0%, 95% CI: 71.5% to 100.0%) BE heads. In heads that could reliably be assessed for BD, BD was detected in 8/9 (88.9%, 95% CI: 51.7% to 99.7%) F heads, 7/10 (70.0%, 95% CI: 34.8% to 93.3%) T heads, and 4/11 (36.4%, 95% CI: 10.9% to 69.2%) BE heads. Tissue depth was reported as mean ± SE followed by 97.5% one-sided upper reference limit (URL). For sows, total tissue thickness differed (P < 0.05) between placements (F: 49.41 ± 2.74 mm, URL: 70.0 mm; T: 62.83 ± 1.83 mm, URL: 76.6 mm; BE: 84.63 ± 3.67 mm; URL: 112.3 mm). Total tissue thickness differed (P < 0.05) between placements for boars (F: 54.73 ± 3.23 mm, URL: 77.6 mm; T: 70.72 ± 3.60 mm, URL: 96.3 mm; BE: 92.81 ± 5.50 mm; URL: 135.3 mm). For swine between 120 and 200 kg BW, the F placement may have the greatest likelihood for successful euthanasia due to the least total tissue thickness and may present less risk for failure than the T and BE placements.

Keywords: boar, captive bolt, euthanasia, sow, swine, welfare

This study evaluated tissue thicknesses, brain area, and brain damage (BD) associated with frontal, temporal, and behind-ear penetrating captive bolt placements for sows and boars weighing < 200 kg. The frontal placement appeared to be more reliable than the alternative temporal or behind-ear placements due to the least tissue for the bolt to travel through to reach the brain, the greatest potential target area, and prevalent BD.

Introduction

Euthanasia is often defined as a “good death” (NPB and AASV, 2016; AVMA, 2020), and is further described by the National Pork Board and American Association of Swine Veterinarians (NPB and AASV, 2016) as “the humane process whereby the pig is rendered insensible, with minimal pain and distress, until death.” A euthanasia procedure must be quick, effective, and reliable to be considered humane (NPB and AASV, 2016). How an animal dies, including the potential for pain and distress, is largely determined by the method of euthanasia selected (AVMA, 2020; WOAH, 2022). It is critical to consider this when choosing euthanasia methods (Anderson et al., 2021a).

Penetrating captive bolt (PCB) is a method often used for the euthanasia of nonsuckling (>5.44 kg and > 3 wk of age [Anderson et al., 2022]) swine. It is approved by AVMA (2020) and jointly approved by NPB and AASV (2016) for use in grow-finish and breeding swine. A PCB placement on the front of an animal’s head is described across all guidance documents (Anderson et al., 2022); from AVMA (2020), NPB and AASV (2016), North American Meat Institute (NAMI, 2021), as well as international guidance documents from the Humane Slaughter Association (HSA, 2016) and European Food Safety Authority (EFSA, 2004; 2020). A single PCB application in this common frontal placement has been evaluated and found to be an effective means of euthanasia for market hogs weighing up to 120 kg (Woods, 2012). However, for sows and boars visually estimated to weigh more than 200 kg, this method was not reliable (Woods, 2012). Additionally, Kramer et al. (2021) reported that a pistol-type PCB applied in the common frontal placement was not 100% effective in causing death for anesthetized sows and boars greater than 200 kg body weight (BW). A pistol-type PCB was found to be effective for market swine weighing up to 120 kg, but not reliable for mature breeding swine >200 kg, while PCB use for smaller breeding swine (those <200 kg BW) was not evaluated (Woods, 2012). This is further exacerbated by the fact that pigs are described as the most difficult animals to stun with a PCB (HSA, 2016). One causative factor of this is that pigs have a smaller brain—the target for PCB use—relative to their size compared to other species (HSA, 2016). Additionally, as pigs age, their skull thickness increases, largely due to the expansion of the frontal sinus cavities (EFSA, 2004; HSA, 2016). A recent review focused on the captive bolt euthanasia of swine (Anderson et al., 2022) revealed that PCB use had not been formally evaluated for swine between 136 and 200 kg BW through scientific investigation.

In addition to the common frontal placement, two alternative PCB placements have been identified: temporal and behind the ear toward the opposite eye (AVMA, 2013); however, in 2020, the AVMA clarified that these alternative placements were intended for use with gunshot only, not PCB (AVMA, 2020). While the temporal placement is only mentioned in AVMA guidelines (2013, 2020), the behind ear placement is mentioned in AVMA guidelines (2013, 2020), as well as in NPB and AASV guidelines (2016), where it is specified as an alternative placement for euthanasia via gunshot. The behind-ear placement was first evaluated by Anderson et al. (2019), who used cadaver heads to assess PCB use at the frontal and behind-ear placement for market hogs estimated to weigh 136 kg. For sows and boars weighing more than 200 kg, the frontal, temporal, and behind-ear placements have been evaluated by Anderson et al. (2021a) and Kramer et al. (2021).

Published data evaluating PCB use at the frontal, temporal, or behind-ear PCB placements for sows and boars <200 kg BW did not appear to exist at the time of this study. Our study was designed to serve as a first step in the scientific evaluation of PCB euthanasia for sows and boars weighing <200 kg BW. There is a need to understand the tissues the bolt must pass through to reach the brain using a non-live animal model. The objectives of this study were to (1) determine the tissue depth, cross-sectional brain area, regions of brain damage (BD), overall BD, and whether the brain was located within the plane of bolt travel for the frontal, temporal, and behind ear PCB placements on cadaver heads from sows and boars <200 kg BW; and (2) to determine the relationships between external dimensional head measurements, BW, and tissue depth parameters associated with these PCB placements. Our hypothesis was that differences in soft tissue thickness, cranial thickness, total tissue thickness, and cross-sectional brain area would be detected between PCB placements.

Materials and Methods

Animal use protocol

It was not necessary to submit an animal use protocol to the University of Wisconsin—River Falls Institutional Animal Care and Use Committee because live animals were not directly manipulated in this study. The pigs from which the heads were obtained were slaughtered at a commercial slaughter establishment under inspection by the United States Department of Agriculture Food Safety and Inspection Service (USDA FSIS) in accordance with the Humane Methods of Slaughter Act (7 USC 1901) (United States House of Representatives Office of the Law Revision Council, 2023) and compliant with associated Federal regulations (9 CFR 313) (United States Electronic Code of Federal Regulations, 2023). The exemption from Institutional Animal Care and Use Committee approval followed the precedent set by Anderson et al. (2019, 2021a, 2021b) and Hamilton et al. (2023).

Description of cadaver heads

To replace the use of live animals to achieve the objectives of this research, cadaver heads were selected, as described by Anderson et al. (2021a) and Hamilton et al. (2023). Briefly, cadaver heads were obtained on five collection days from a total of 30 sows (average BW = 165.8 ± 21.4 kg, mean ± SD) and 30 boars (average BW = 173.6 ± 22.4 kg, mean ± SD) that were electrically stunned and slaughtered at a regional commercial processing facility. The specific age and parity of each source animal were unavailable, but all source animals were cull sows and boars. A power calculation to determine sample size was conducted using the POWER procedure of SAS 9.4 (Statistical Analysis System Institute, Inc., Cary, NC) with the following parameters: detectable difference of 12.7, SD of 9.893, power of 0.8. The detectable difference was derived from cranial thickness measurements of boars weighing more than 200 kg BW in the FRONTAL and TEMPORAL PCB placements, and the SD value was back-calculated from the SE values reported for the same measurements (Anderson et al., 2021a). Hot carcass weight (HCW) of skinned carcasses and the average dressing percentage from the slaughter establishment (58%) were used to calculate the estimated live weight for each source animal; to account for the neck tissue remaining on the heads, an additional 4.535 kg were added to the weight of each pig (formula: estimated BW = HCW [kg]/ 0.58 + 4.535 kg) (Anderson et al., 2021a). Heads had the skin on, intact jowls, and were not scalded; approximately 6 cm of neck tissue was left behind the ear to prevent soft tissue distortion at the PCB application site. All heads were placed in large storage totes with secured lids (Sterilite 1,466 to 27 Gallon Industrial Tote, Sterilite Corp., Townsend, MA) with two heads per tote, and stored at ambient temperature for approximately 4 h postmortem prior to unrefrigerated transport (distance traveled: 188 km; duration: approximately 2 h) to the University of Wisconsin—River Falls Meat Science Laboratory and Animal Welfare Lab, as described by Anderson et al. (2021a). Heads were stored in the storage totes with the lids slightly offset inside a walk-in cooler for approximately 61 h at 2 to 4 °C prior to PCB application and head processing to improve the rigidity of brain tissue (Anderson et al, 2021a). After post-application head processing, the mean temperature of the exposed internal cranial surface was 7.61 ± 1.12 °C (mean ± SD) and did not differ between sex and treatments (Table 1). Between 19 and 30 heads were obtained for each head processing date, but only heads from animals with an estimated BW of less than 200 kg were enrolled in this study. As a result, 7 to 17 heads were included for each head processing date.

Table 1.

Source animal and cadaver head characteristics from mature sows and boars¹ (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements² and sectioned by band saw following the plane of bolt entry

Sex	Dependent variable	PCB placement
Sex	Dependent variable	FRONTAL			TEMPORAL			BEHIND EAR
		n	LS means	SE	n	LS means	SE	n	LS means	SE
SOWS
	Brain Temp, ° C	10	8.03	0.37	10	7.52	0.36	10	8.36	0.24
	Estimated BW, kg	10	172.14	6.10	10	159.12	7.16	10	166.04	7.96
	Head weight, kg	10	16.86	1.31	10	17.42	1.09	10	17.73	1.22
	Distance between optic orbits, cm	10	14.70	0.55	10	13.99	0.38	10	14.69	0.62
	Snout to poll distance, cm	10	29.22	0.54	10	29.12	0.68	10	29.92	0.69
	Maximum deflection distance, cm	10	3.84	0.34	10	3.70	0.25	10	4.21	0.20
BOARS
	Brain Temp, ° C	9	7.94	0.46	10	7.02	0.23	11	6.91	0.26
	Estimated BW, kg	9	172.04	10.12	10	172.22	5.99	11	176.06	4.87
	Head weight, kg	9	19.33	1.65	10	20.03	1.75	11	18.10	1.12
	Distance between optic orbits, cm	9	15.44	0.58	10	15.43	0.49	11	15.06	0.36
	Snout to poll distance, cm	9	29.12	0.66	10	28.66	0.91	11	28.26	1.16
	Maximum deflection distance, cm	9	4.33	0.40	10	4.65	0.37	11	3.61	0.27

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¹Comparisons between sexes were not conducted because it is unknown how morphological changes in head conformation change as sows and boars continue to grow heavier than the sows and boars that provided the heads for this study.

²Placements: FRONTAL—Medial bolt entry approximately 3.5 cm superior to the optic orbits at midline perpendicular with the external surface of the head; TEMPORAL—Bolt entry at the depression located between the right eye and right ear.

BEHIND EAR—Bolt entry directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye.

^a,b,cSuperscripts that differ within a row identify significant differences between means within dependent variables across placements (P ≤ 0.05).

Description of captive bolt tool, placement, and treatment assignment

The PCB device, placements, and application process used in this study were also used by Anderson et al. (2021a). All PCB applications were made using a Jarvis Model PAS—Type P 0.25R Caliber Captive Bolt Pistol (Order #: 4144035, Jarvis Corp., Middletown, CT) equipped with a Long Stunning Rod Nosepiece Assembly (Order #: 3116605, Jarvis Corp.) and Jarvis Orange Powder Cartridges 0.25R Caliber, 3.5 GR (Order #: 1176019, Jarvis Corp). Orange cartridges were selected based on manufacturer recommendations for mature sows and boars, coupled with the fact that this is the highest power cartridge approved by the manufacturer for repeated use of the PCB used in this study. The predicted bolt travel distance for the PCB device with the stunning rod and cartridge combination used in our study was 76.2 mm (M. Abdul, Jarvis Corp., Middletown, CT, personal communication). Three PCB placement treatments were applied to heads in this study (Figure 1): FRONTAL—shot placed 3.5 cm superior to the optic orbits at midline (Woods et al., 2010), TEMPORAL—shot placed at the depression caudal to the lateral canthus of the eye within the plane between the lateral canthus and the base of the ear (Anderson et al., 2021a), or BEHIND EAR—shot placed directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye (Anderson et al., 2019; AVMA, 2013).

Figure 1. — Penetrating captive bolt (PCB) placement placements. (A) FRONTAL—shot placed 3.5 cm superior to the optic orbits at the midline; (B) TEMPORAL—shot placed at the depression posterior to the lateral canthus of the eye within the plane between the lateral canthus and the base of the ear; (C) BEHIND EAR—shot placed directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye. All heads were secured within a custom-fabricated stainless steel brace for PCB application, shown here for each of the PCB placements. The brace in this image was designed to hook around the edge of the table on which it was located to prevent shifting during head positioning and PCB application.

Prior to activation, the muzzle of the PCB was placed firmly against the head for all PCB placements. A custom-fabricated benchtop-mounted brace of stainless steel was bent to form a corner so that each head could be braced against the corner and firmly secured during each PCB application. This brace was hooked around the edge of the table where it was located to prevent movement during PCB application. All PCB applications were made by a single individual who had used the same device in earlier work (Anderson et al. 2021a; 2021b).

Heads were assigned to their respective placements by sorting each day’s sample group by estimated live weight, then randomly allocating three placements to each cluster of three heads working from lightest to heaviest using a random number generator in Excel (Microsoft Corp., Spokane, WA); each head received a single PCB application in one of the three placements evaluated in this study. Blinding was not possible once heads had received a PCB placement because the application site was obvious to any observer. As such, the individuals performing tissue thickness measurements, cross-sectional brain area measurements, and head image assessment were not blinded to the PCB placement.

The average bolt speed for the PCB was tested using a Jarvis PAS Stunning System Tester (Order #: 4116001, Jarvis Corp., Middletown, CT) before the first PCB application at the beginning of each sampling day and before cleaning at the end of each sampling day. Average bolt speed was calculated from three successive readings at each time point. The average bolt speed for all sampling days was 49.11 ± 2.66 m/s (mean ± SD). The PCB device and cartridge combination used in this study had an expected bolt speed of 51.82 ± 3.05 m/s (M. Abdul, Jarvis Corp., Middletown, CT, personal communication).

Post-application head processing and measurements

Each head was split along the bolt path following the PCB application with a Hobart 6801 Vertical Meat Band Saw (Hobart, Troy, OH) equipped with a 0.06 mm thick, 360.68 mm long blade with 4 teeth/2.54 cm and a 3-degree hook angle (Product #: C78529545, Bunzl Processor Division, Riverside, MO). After each split, a 150 mm digital caliper (HC Kenshin Electronic Digital Vernier Caliper, HC Kenshin, HuiChuang Technology, Fujia, China) was used to measure soft tissue thickness (mm) and cranial thickness (mm) for both sides of each head, as described by Hamilton et al. (2023). Soft tissue thickness refers to the tissue from the application site to the exterior surface of the cranium (Anderson et al, 2019, 2021a, 2021b; Hamilton et al., 2023); cranial thickness refers to the exterior surface of the cranium to the interior surface of the cranium along the bolt path (Anderson et al., 2019, 2021a, 2021b; Hamilton et al., 2023). These measurements were collected on both sides of the exposed bolt path, as described by Anderson et al. (2019, 2021a, 2021b) and Hamilton et al. (2023) and were averaged prior to statistical analysis. In instances where the brain cavity was not reached by the bolt, measurements were collected for the entire distance in alignment with the existing bolt path (Anderson et al., 2021a). If the bolt path was not in alignment with the brain cavity, soft tissue thickness and cranial thickness were not recorded. Total tissue thickness (mm) was determined by the summation of the soft tissue and cranial thickness for each head; this measurement referred to the total soft tissue thickness and cranial thickness from the site of PCB application to the interior surface of the cranium, along the bolt path (Anderson et al., 2019, 2021a, 2021b; Hamilton et al., 2023).

Cross-sectional brain area (mm²) refers to the cross-sectional surface area of the exposed brain within the plane of bolt travel as described by Anderson et al. (2019; 2021a); these measurements were calculated for both sides of each head and averaged prior to statistical analysis. A single observer (KNA) performed all cross-sectional brain area measurements. Tissue depth measurements and cross-sectional brain areas can be observed in Figure 2 (FRONTAL), Figure 3 (TEMPORAL), and Figure 4 (BEHIND EAR).

Figure 2. — Frontal tissue measurements. Soft tissue thickness—the tissue from the application site on the surface of the skin to the exterior surface of the cranium. Cranial thickness—the tissue from the exterior surface of the cranium along the bolt path. Brain area—the cross-sectional surface area of the exposed brain within the plane of bolt travel.

Figure 3. — Temporal tissue thickness measurements. Soft tissue thickness—the tissue from the application site on the surface of the skin to the exterior surface of the cranium. Cranial thickness—the tissue from the exterior surface of the cranium along the bolt path. Brain area—the cross-sectional surface area of the exposed brain within the plane of bolt travel.

Figure 4. — Behind ear tissue measurements. Soft tissue thickness—the tissue from the application site on the surface of the skin to the exterior surface of the cranium. Cranial thickness—the tissue from the exterior surface of the cranium along the bolt path. Brain area—the cross-sectional surface area of the exposed brain within the plane of bolt travel.

After each cut, digital images were collected using a digital camera (Olympus Tough TG-6 Waterproof Camera, OM Digital Solutions Corp., Tokyo, Japan) from both sides of each intracranial surface and both with and without the brain, as described by Anderson et al. (2021a). In addition, thermal images (Model E8, FLIR Systems, Boston, MA) were collected from both sides of each exposed intracranial surface for temperature assessment; thermal images were only collected with the brain for each head. Brain temperature was determined using these thermal images. For both sows and boars, there was no evidence to support a difference (P < 0.05) in brain temperature between PCB placements (Table 1); the average brain temperature for sow heads was 7.97 ± 0.32 °C (mean ± SE) and the average brain temperature for boar heads was 7.26 ± 0.31 °C (mean ± SE). All images were taken with the camera positioned 58.0 cm directly above and perpendicular to the exposed cut surface (Anderson et al., 2021a).

BD assessment

Methods for assessing regions of BD, overall BD, and brain contact plane were adapted from Anderson et al. (2021a); these were assessed using digital images of the brain collected at the time of head processing. The frontal lobe, parietal lobe, occipital lobe, corpus callosum, diencephalon, mesencephalon, brainstem (the region including the pons and medulla), and the cerebellum (adapted from Wagner et al., 2019) were assessed for physical damage on a yes/no basis, where yes meant there was visually detectable tissue damage to a given region of the brain and no meant there was no visually detectable tissue damage to a given region of the brain. Overall BD was also determined on a yes/no basis, where yes meant that there was visually detectable damage to at least one region of the brain and no meant there was no visually detectable damage to at least one region of the brain.

To assess damage to each region of the brain, brain maps developed by Anderson et al. (2021a) for the FRONTAL, TEMPORAL, and BEHIND EAR PCB placements were used. For the FRONTAL placement, the parietal lobe, frontal lobe, occipital lobe, corpus callosum, mesencephalon, diencephalon, brainstem, and cerebellum were assessed for damage. For the TEMPORAL placement, if only the parietal lobe was visible, that was the only region assessed for damage; for heads where additional regions could be seen on the split head, the parietal lobe, occipital lobe, corpus callosum, and diencephalon were assessed for damage. For the BEHIND EAR placement, the parietal lobe, temporal lobe, occipital lobe, corpus callosum, diencephalon, and mesencephalon were assessed for damage. Following the procedures outlined by Anderson et al. (2021a), only brain regions or structures that were included in the brain map and assessment for each PCB placement were included in analyses.

Images of each head were also assessed to determine brain contact plane—whether the bolt path was in the plane of the brain. When the bolt reached the brain or would have been long enough to pass through the soft tissue and cranium, the bolt path was considered to have been in the plane of the brain. When the bolt path did not hit the brain, or would not have sufficient bolt length, the bolt path was considered to not be in the plane of the brain.

External head measurements

The following external head measurements were collected using a flexible measuring tape for all heads (Singer 218 60 in, The Singer Company Ltd., Boston, MA): distance between optic orbits (cm), snout to poll distance (cm), and maximum deflection distance (cm). These measurements were adapted from Anderson et al. (2021a). Distance between optic orbits refers to the distance between the medial aspects of the optic orbits. Snout-to-poll distance refers to the distance from the tip of the snout to the first point of contact between a taught measurement tape at the crest of the head. Maximum deflection distance refers to the maximum distance from a straight edge that was placed between the tip of the snout and the poll or first point where the straight edge touched the head when placed from the tip of the snout. Measurements of distance between optic orbits, snout-to-poll distance, and maximum deflection distance were collected in duplicate by a team of trained observers and were averaged prior to statistical analysis. The mean interobserver percent coefficients of variation were 5.1%, 10.0%, and 11.2% for snout-to-poll distance, distance between optic orbits, and maximum deflection, respectively. Head weight (kg) was also collected for all heads via a calibrated benchtop scale. The ID tag associated with each head was not marked with the PCB placement until after external head measurements had been taken, so the individuals taking these measurements were blinded to PCB placement.

Statistical analyses

Continuous data outcomes (BW, head weight, distance between optic orbits, snout to poll distance, maximum deflection distance, soft tissue thickness, cranial thickness, total tissue thickness, and cross-sectional brain area) for PCB placement treatment (FRONTAL, TEMPORAL, and BEHIND EAR) effects were analyzed using models constructed within the MIXED procedure of SAS Enterprise Guide 7.1 (Statistical Analysis System Institute, Inc., Cary, NC). A repeated statement with grouping by treatment and the Satterthwaite method for degrees of freedom was used to account for unequal variances by treatment. Models included placement treatment effects (FRONTAL, TEMPORAL, and BEHIND EAR) only. Three heads, two TEMPORAL boar and one FRONTAL boar, were excluded from tissue depth analyses because tissue depth parameters could not be recorded. In addition, three different heads, two FRONTAL sow, and one FRONTAL boar, were excluded from the analysis for cross-sectional brain area because brain area could not be reliably measured. Due to unknown sex-related morphological changes as swine mature, comparisons between sexes were not conducted, as these changes could not accurately be factored into the model, as described by Anderson et al. (2021a). Describing differences between placements within sex was our focus. Mean separation was determined via Students T-tests, protected by the Bonferroni-Holm adjustment. Differences between means were recognized as significant when P < 0.05.

To estimate the bolt length needed to effectively reach the brain for the majority of sows and boars weighing more than 120 kg, a 97.5% one-sided reference range was computed using a t-based prediction interval for normally distributed data with unknown mean and standard deviation (Horn, 1988), along with a 90% confidence interval for the upper reference limit (URL) for soft tissue thickness, cranial thickness, and total tissue thickness for the FRONTAL, TEMPORAL, and BEHIND EAR PCB placements, as described by Anderson et al. (2021a). The tidyverse and ggbeeswarm packages within R version 4.2.2 (R Core Team, 2023) via R Studio version 2023.03.0 (R Core Team, 2023) were used to calculate URLs, the 90% CIs around the URL values (URL 90% CI), and associated plots. URL calculations were performed separately for sows and boars.

The occurrence of BD, regions of BD, and brain contact plane were calculated and 95% confidence intervals were determined using the Clopper-Pearson exact method within the binom package (version 1.1) in R version 4.2.2 (R Core Team, 2023) via R Studio version 2023.03.0 (R Core Team, 2023). One head (TEMPORAL sow) was excluded from the analysis for occurrence of BD and regions of BD because damage could not be reliably assessed. Statistical comparisons between placements for BD, regions of BD, and brain contact plane were not made due to different planes of bolt travel that resulted in varying regions of the brain that were accessible to the bolt and therefore assessed for damage across the three placements.

The relationships between BW, head weight, and external head measurements (distance between optic orbits, snout to poll distance, and maximum deflection distance) were assessed for correlations with soft tissue thickness, cranial thickness, and total tissue thickness for all head placement via simple linear regression using the Regression procedure in SAS (Statistical Analysis System Institute, Inc., Cary, NC). Correlations were recognized as significant when P < 0.05.

Results and Discussion

Source animal and cadaver head characteristics

Estimated BW, head weight, and external head measurements for both sows and boars can be observed in Table 1. All estimated BW, head weight, and external head measurements—distance between optic orbits, snout to poll distance, and maximum deflection distance—are reported as mean ± SE.

There was no evidence to support a significant difference in estimated BW between PCB placements for either sows (P = 0.4009) or boars (P = 0.8613). Estimated BW was 172.14 ± 6.10 kg for sow heads that received the FRONTAL placement, 159.12 ± 7.16 kg for sow heads that received the TEMPORAL placement, 166.04 ± 7.96 kg for sow heads that received the BEHIND EAR placement, 172.04 ± 10.12 kg for boar heads that received the FRONTAL placement, 172.22 ± 5.99 kg for boar heads that received the TEMPORAL placement, and 176.06 ± 4.87 kg for boar heads that received the BEHIND EAR placement. There was also no evidence to support a significant difference in head weight between PCB placements for either sows (P = 0.8893) or boars (P = 0.6198). Head weight was 16.86 ± 1.31 kg for sow heads that received the FRONTAL placement, 17.42 ± 1.09 kg for sow heads that received the TEMPORAL placement, and 17.73 ± 1.22 kg for sow heads that received the BEHIND EAR placement, 19.33 ± 1.65 kg for boar heads that received the FRONTAL placement, 20.03 ± 1.75 kg for boar heads that received the TEMPORAL placement, and 18.10 ± 1.12 kg for boar heads that received the BEHIND EAR placement. This study addressed a population of animals that have historically been excluded, without clear reason, from evaluations of PCB use for swine (described by Anderson et al., 2021a, 2022).

There was no evidence (P < 0.05) to support a difference in distance between optic orbits, snout-to-poll distance, or maximum deflection distance between the FRONTAL, TEMPORAL, or BEHIND EAR placements for either sows or boars. Distance between optic orbits was 14.70 ± 0.55 cm for sow heads that received the FRONTAL placement, 13.99 ± 0.38 cm for sow heads that received the TEMPORAL placement, and 14.69 ± 0.62 for sow heads that received the BEHIND EAR placement (P = 0.4690). Distance between optic orbits was 15.44 ± 0.58 cm for boar heads that received the FRONTAL placement, 15.43 ± 0.49 cm for boar heads that received the TEMPORAL placement, and 15.06 ± 0.36 cm for boar heads that received the BEHIND EAR placement (P = 0.7773). Snout to poll distance was 29.22 ± 0.54 cm for sow heads that received the FRONTAL placement, 29.12 ± 0.68 cm for sow heads that received the TEMPORAL placement, and 29.92 ± 0.69 cm for sow heads that received the BEHIND EAR placement (P = 0.6636). Snout-to-poll distance was 29.12 ± 0.66 cm for boar heads that received the FRONTAL placement, 28.66 ± 0.91 cm for boar heads that received the TEMPORAL placement, and 28.26 ± 1.16 cm for boar heads that received the BEHIND EAR placement (P = 0.7966). Maximum deflection distance was 3.84 ± 0.34 mm for sow heads that received the FRONTAL placement, 3.70 ± 0.25 cm for sow heads that received the TEMPORAL placement, and 4.21 ± 0.20 cm for sow heads that received the BEHIND EAR placement (P = 0.2713). Maximum deflection distance was 4.33 ± 0.40 cm for boar heads that received the FRONTAL placement, 4.65 ± 0.37 cm for boar heads that received the TEMPORAL placement, and 3.61 ± 0.27 cm for boar heads that received the BEHIND EAR placement (0.0823). This suggests that varying phenotypic characteristics of the head (e.g., “plank” or “dish” profiles) were evenly distributed across PCB placement treatments for sow and boar heads. Hamilton et al. (2023) reported maximum deflection distances of 3.31 and 3.08 cm for physically castrated barrows and immunocastrated boars, respectively. The maximum deflection distances observed in the present study were greater than those reported by Hamilton et al. (2023), suggesting that the “dish” shape may become more pronounced as pigs mature.

Tissue and cranial measurements

Tissue thickness measurements for both sows and boars can be observed in Table 2 (means ± SEs) and Table 3 (97.5% reference interval upper limit [URL] and the 90% confidence interval for the URL [URL 90% CI]). All tissue thickness measurements are reported as mean ± SE; URL; URL 90%. Cross-sectional brain areas for both sows and boars can also be observed in Table 2 and are reported as means ± SE.

Table 2.

Soft tissue thickness, cranial thickness, total tissue thickness, and cross-sectional brain area of cadaver heads from mature sows and boars¹ (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements² and sectioned by band saw following the plane of bolt entry

Sex	Dependent variable	PCB placement
		FRONTAL			TEMPORAL			BEHIND EAR
		n	LS means	SE	n	LS means	SE	n	LS means	SE
SOWS
	Soft tissue thickness, mm	10	7.30^b	0.51	10	49.30^a	3.01	10	47.80^a	3.22
	Cranial thickness, mm	10	42.11^a	2.95	10	13.52^b	2.22	10	39.97^a	2.18
	Total tissue thickness, mm	10	49.41^c	2.74	10	62.83^b	1.83	10	84.76^a	3.67
	Cross-sectional brain area, mm²	8	4,229.38^a	83.71	10	1,334.48^c	217.47	10	2,465.38^b	58.90
BOARS
	Soft tissue thickness, mm	8	10.64^b	1.12	8	52.63^a	3.55	11	61.24^a	6.20
	Cranial thickness, mm	8	44.09^a	3.60	8	18.09^c	3.04	11	31.57^ab	3.31
	Total tissue thickness, mm	8	54.73^c	3.23	8	70.72^b	3.60	11	92.81^a	5.50
	Cross-sectional brain area, mm²	8	4,217.99^a	69.21	10	1,155.24^c	84.26	11	2,274.47^b	175.54

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BEHIND EAR—Bolt entry directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye.

^a,b,cSuperscripts that differ within a row identify significant differences between means within dependent variables across placements (P ≤ 0.05).

Table 3.

Upper 97.5% reference interval limits (URL) and associated 90% confidence intervals (URL 90% CI) for tissue depth parameters of cadaver heads from sows and boars¹ <200 kg BW assigned to three penetrating captive bolt (PCB) placements² and sectioned by band saw following the plane of bolt entry

Sex	Dependent variable	PCB placement
		FRONTAL			TEMPORAL			BEHIND EAR
		n	URL	URL 90% CI	n	URL	URL 90% CI	n	URL	URL 90% CI
SOWS
	Soft tissue thickness, mm	10	11.1	9.7 to 12.6	10	71.9	63.4 to 80.4	10	72.0	62.9 to 81.0
	Cranial thickness, mm	10	64.2	55.9 to 72.5	10	30.2	23.9 to 36.4	10	53.3	47.2 to 59.5
	Total tissue thickness, mm	10	70.0	62.3 to 77.7	10	76.6	71.4 to 81.7	10	112.3	102.0 to 122.6
BOARS
	Soft tissue thickness, mm	8	18.6	15.4 to 21.7	8	77.8	67.8 to 87.8	10	109.1	91.7 to 126.5
	Cranial thickness, mm	8	69.7	59.5 to 79.8	8	39.7	31.1 to 48.2	10	57.1	47.8 to 66.5
	Total tissue thickness, mm	8	77.6	68.5 to 86.7	8	96.3	86.2 to 106.4	10	135.3	119.8 to 150.7

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²Placements: FRONTAL—Medial bolt entry approximately 3.5 cm superior to the optic orbits at midline perpendicular with the external surface of the head.

TEMPORAL—Bolt entry at the depression located between the right eye and right ear.

BEHIND EAR—Bolt entry directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye.

BW, body weight.

For sow and boar heads, total tissue thickness and cross-sectional brain area were significantly different (P < 0.05) between the FRONTAL, TEMPORAL, and BEHIND EAR placements. The least (P < 0.05) soft tissue thickness was observed in the FRONTAL placement (mean ± SE; sows: 7.30 ± 0.51 mm, URL: 11.1 mm, URL 90% CI: 9.7 to 12.6 mm; boars: 10.64 ± 1.12 mm, URL: 18.6 mm, URL 90% CI: 15.4 to 21.7 mm). Soft tissue thickness was significantly greater (P < 0.05) in the TEMPORAL (sows: 49.30 ± 3.01 mm, URL: 71.9 mm, URL 90% CI: 63.4 to 80.4 mm; boars: 52.63 ± 3.55 mm, URL: 77.8 mm, URL 90% CI: 67.8 to 87.8 mm) and BEHIND EAR placements (sows: 47.80 ± 3.22 mm, URL: 72.0 mm, URL 90% CI: 62.9 to 81.0 mm; boars: 61.24 ± 6.20 mm, URL: 109.1 mm, URL 90% CI: 91.7 to 126.5 mm), though there was not sufficient evidence to support a significant difference (P > 0.05) in soft tissue thickness between these placements for either sows or boars. Cranial thickness was least (P < 0.05) in the TEMPORAL placement (sows: 13.52 ± 2.22 mm, URL, 30.2 mm, URL 90% CI: 23.9 to 36.4 mm; boars: 18.09 ± 3.04 mm, URL: 39.7 mm, URL 90% CI: 31.1 to 48.2 mm). Cranial thickness was significantly greater (P < 0.050) at the FRONTAL (sows: 41.11 ± 2.95 mm, URL: 64.2 mm, URL 90% CI: 55.9 to 75.2 mm; boars: 44.09 ± 3.60 mm, URL: 69.7 mm, URL 90% CI: 59.5 to 79.8 mm) and BEHIND EAR placements (sows: 39.97 ± 2.18 mm, URL: 53.3 mm, URL 90% CI: 47.2 to 59.5 mm; boars: 31.57 ± 3.31 mm, URL: 57.1 mm, URL 90% CI: 47.8 to 66.5 mm); however, there was no evidence to support a significant difference (P > 0.05) in cranial thickness between the FRONTAL and BEHIND EAR placements for either sows or boars. Total tissue thickness was least (P < 0.05) in the FRONTAL placement (sows: 49.41 ± 2.74 mm, URL: 70.0 mm, URL 90% CI: 62.3 to 77.7 mm; boars: 54.73 ± 3.33 mm, URL: 77.6 mm, URL 90% CI: 68.5 to 86.7 mm), followed by the TEMPORAL placement (sows: 62.83 ± 1.83 mm, URL: 76.6 mm, URL 90% CI: 71.4 to 81.7 mm; boars: 70.72 ± 3.60 mm, URL: 96.3 mm, URL 90% CI: 71.4 to 81.7 mm), and was greatest in the BEHIND EAR placement (sows: 84.76 ± 3.67 mm; URL: 112.3 mm; URL 90% CI: 102.0 to 122.6 mm; boars: 92.81 ± 5.50 mm; 135.3 mm; URL 90% CI: 119.8 to 150.7 mm). These findings are in alignment with those of Anderson et al. (2019, 2021a) who observed the least total tissue thickness in the frontal placement for market hogs, as well as sows and boars >200 kg. The least total tissue thickness at the frontal placement in this study and the Anderson et al. (2019, 2021a) studies suggest that the frontal placement may be more reliable in reaching the brain than alternative PCB placements. Cranial thickness was measured on sows and boars > 200 kg BW that received either a frontal, temporal, or behind-ear PCB application by Kramer et al. (2021); however, this was not measured at the PCB application site, but rather at a consistent location for all PCB placements, so comparisons to our findings cannot be made. Additionally, Kramer et al. (2022) measured cranial thickness for sows and boars >200 kg that received either a frontal PCB application or an electric stun, but these measurements were not made at the frontal PCB placement, so comparisons to our findings cannot be made.

The URL values reported here are of high value to PCB device manufacturers and the individuals tasked with selecting PCB devices for euthanasia or stunning, as described by Anderson et al. (2021a). These values can be used as a predictor of whether a PCB device with a known penetration depth, or bolt travel distance, would have the capacity to reach the brain in 97.5% of sows or boars <200 kg BW in the FRONTAL, TEMPORAL, or BEHIND EAR PCB placements. Our findings suggest that a penetration depth of 70.0 mm would be required to reach the brain in the FRONTAL PCB placement, a penetration depth of 76.6 mm would be required to reach the brain in the TEMPORAL PCB placement, and a penetration depth of 112.3 mm would be required to reach the brain in the BEHIND EAR PCB placement, for 97.5% of sows. Our findings suggest a penetration depth of 77.6 mm would be required to reach the brain in the FRONTAL PCB placement, a penetration depth of 96.3 mm would be required to reach the brain in the TEMPORAL PCB placement, and a penetration depth of 135.3 mm would be required in the BEHIND EAR PCB placement to reach the brain, for 97.5% of boars. All URL values, URL 90% CIs, and the sample distributions for tissue thickness measurements at each PCB placement can be viewed in Figure 5. For both sows and boars, these findings are similar to those of Anderson et al. (2021a), who described that the greatest penetration depth was required to reach the brain at the BEHIND EAR placement and the least penetration depth was required to reach the brain at the FRONTAL placement.

Figure 5. — Upper 97.5% reference interval limits (URL, black dot) and associated 90% confidence intervals (URL 90% CI, black bars), along with data distribution for tissue depth parameters of cadaver heads from mature sows and boars (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements and sectioned by band saw following the plane of bolt entry.

Cross-sectional brain area was greatest (P < 0.05) in the FRONTAL placement (sows: 4,229.38 ± 83.71 mm²; boars: 4,217.99 ± 69.21 mm²), followed by the BEHIND EAR placement (sows: 2,465 ± 58.90 mm²; boars: 2,274.47 ± 175.54 mm²), and was least in the TEMPORAL placement (sows: 1,334.48 ± 217.47 mm²; boars: 1,155.24 ± 84.26 mm²). These findings align with those of Anderson et al. who reported the greatest brain area in the frontal placement for both market hogs (Anderson et al., 2019) and sows and boars >200 kg (Anderson et al., 2021a). To the best of our knowledge, no other literature has compared brain area at the frontal and alternative PCB placements for swine, although pigs are described as having a small brain relative to the size of their head (HSA, 2016).

Brain tissue damage assessment

Brain contact plane results for sows and boars can be observed in Table 4. The bolt path was in the plane of the brain for all sow heads that received the FRONTAL, TEMPORAL, and BEHIND EAR PCB applications (10 of the 10, 100.0%, 95% CI: 69.2% to 100.0% each). These findings are similar to those of Anderson et al. (2021a) who observed that 100.0% (42 of the 42), 97.5% (39 of the 40), and 87.2% (34 of the 39) of sow heads shot in the FRONTAL, TEMPORAL, and BEHIND EAR PCB placements had the bolt path located within the plane of the brain. The bolt path was within the plane of the brain for eight of the nine (88.9%, 95% CI: 51.8% to 99.7%) boar heads that received the FRONTAL PCB application. For one boar head that received a FRONTAL PCB application, the bolt path was too far posterior to be in the plane of the brain. The bolt path was in the plane of the brain for 9 of the 10 (90.0%, 95% CI: 55.5 to 99.7%) boar heads that received the TEMPORAL PCB application. For one boar head that received a TEMPORAL PCB application, the bolt path was too dorsal to be in the plane of the brain. The bolt path was in the plane of the brain for 11 of the 11 (100.0%, 95% CI: 71.5 to 100.0%) boar heads that received the BEHIND EAR PCB application. These findings are similar to those of Anderson et al. (2021a) who observed that 100.0% of boar heads shot in the FRONTAL (17 of the 17), TEMPORAL (18 of the 18), and BEHIND EAR (14 of the 14) had the bolt path located within the plane of the brain. Anderson et al. (2019) did not record whether the bolt path was located within the plane of bolt travel; however, they did report bolt-brain contact and found a higher incidence of bolt-brain contact in market hog heads that received a FRONTAL PCB application (100.0%, 11 of the 11) than a BEHIND EAR PCB application (66.7%, 8 of the 12). Additionally, Hamilton et al. (2023) reported that all heads from physically castrated market barrows and immunocastrated boars that received a FRONTAL PCB application had the theoretical bolt path located within the plane of the brain (100.0%, 42 of the 42). Woods (2012) and Kramer et al. (2021, 2022) did not report whether the bolt path was located within the plane of the brain in their studies.

Table 4.

Percentage of cadaver heads from mature sows and boars (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements¹ in which the brain was located within the plane of bolt travel

Sex	PCB placement	Brain within plane of bolt travel
Sex	PCB placement	Proportion (observed/total)	Percentage	95% CI²
SOWS
	FRONTAL	10/10	100.0	69.2% to 100.0%
	TEMPORAL	10/10	100.0	69.2% to 100.0%
	BEHIND EAR	10/10	100.0	69.2% to 100.0%
BOARS
	FRONTAL	8/9	88.9	51.8% to 99.7%
	TEMPORAL	9/10	90.0	55.5% to 99.7%
	BEHIND EAR	11/11	100.0	71.5% to 100.0%

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¹Placements: FRONTAL—Medial bolt entry approximately 3.5 cm superior to the optic orbits at midline perpendicular with the external surface of the head; TEMPORAL—Bolt entry at the depression located between the right eye and right ear; BEHIND EAR—Bolt entry directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye.

²95% confidence interval for the percentage of heads with the brain in the plane of bolt travel.

Overall BD results can be observed in Table 5. BD was detected in 10 of the 10 (100.0%, 95% CI: 69.2% to 100.0%) sow heads that received the FRONTAL PCB application, 9 of the 9 (100.0%, 95% CI: 66.4% to 100.0%) sow heads that received the TEMPORAL PCB application, and 0 of the 10 (0.0%, 95% CI: 0.0% to 30.1%) sow heads that received the BEHIND EAR PCB application. While BD results for sow heads that received FRONTAL and TEMPORAL PCB placements are in alignment with the brain contact plane findings, it is noteworthy that the BD results and brain contact plane results for sow heads that received the BEHIND EAR PCB placement are quite different (0.0% and 100.0%, respectively). This suggests that the PCB device used in our study may not have sufficient bolt travel distance to reach the brain, or to cause bone fragmentation that reaches the brain. Anderson et al. (2021a) found that 96.2% (25 of the 26) sow heads shot in the FRONTAL PCB placement had visible BD, similar to the findings of the current study. However, the observed prevalence of BD for sow heads that received a TEMPORAL PCB application was higher in our study than what Anderson et al. (2021a) observed (68.6%, 24 of the 35) and the observed prevalence of BD for sow heads that received a BEHIND EAR PCB placement was higher in the Anderson et al. (2021a) study (12.5%, 5 of the 40) than the current study.

Table 5.

Occurrence of visible brain damage in cadaver heads from mature sows and boars (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements¹ and sectioned by band saw following the plane of bolt entry

Sex	PCB placement	Overall brain damage
Sex	PCB placement	Proportion (observed/total)	Percentage	95% CI²
SOWS
	FRONTAL	10/10	100.0	69.2% to 100.0%
	TEMPORAL	9/9	100.0	66.4% to 100.0%
	BEHIND EAR	0/10	0.0	0.0% to 30.1%
BOARS
	FRONTAL	8/9	88.9	51.7% to 99.7%
	TEMPORAL	7/10	70.0	34.8% to 93.3%
	BEHIND EAR	4/11	36.4	10.9% to 69.2 %

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²95% Confidence interval for the percentage of heads with overall brain damage.

BD was detected in 8 of the 9 (88.9%, 95% CI: 51.7% to 99.7%) boar heads that received the FRONTAL PCB application, 7 of the 10 (70.0%, 95% CI: 34.8% to 93.3%) boar heads that received the TEMPORAL PCB application, and 4 of the 11 (36.4%, 95% CI: 10.9% to 69.2%) boar heads that received the BEHIND EAR PCB application. BD was observed in all boar heads that received the FRONTAL PCB placement and had the bolt path located within the plane of the brain (88.9%, 8 of the 9), but BD was not observed in all heads that received the TEMPORAL or BEHIND EAR PCB placements and had the bolt path located within the plane of the brain. Anderson et al. (2021a) observed a high prevalence (91.7%, 11 of the 12) of BD in boar heads that received a FRONTAL PCB application, similar to our current findings. Anderson et al. (2021a) observed a lower prevalence (13.3%, 2 of the 15) of BD to boar heads that received the TEMPORAL application than we did in the current study, but observed a higher prevalence (50.0%, 7 of the 14) of BD in boar heads that received a BEHIND EAR PCB application than we did in the current study.

Woods (2012) assessed BD for 30 anesthetized swine, ranging from 15 to < 200 kg BW, that received a single PCB application in the FRONTAL placement using a three-point traumatic brain injury (TBI) scoring system that was adapted from Millar and Mills (2000) and found that the 24 pigs that were successfully euthanized with a single PCB application had some level of TBI. Using the same TBI scoring system as Woods (2012), Kramer et al. (2021) found that sows tended to have a higher TBI score than boars. In addition to assessing overall BD, additional information can be gained by understanding the regions and structures of the brain where BD occurs at a given PCB placement. Anderson et al. (2021a) described that limited information can be gained from an overall or summative scoring of BD, as it is unknown where the damage occurred. Both the brainstem and diencephalon are regions of the brain, which have been associated with the presence or absence of sensibility. The brainstem contains the reticular formation which then connects to the cerebral cortex via the ascending reticular activating system (ARAS), which travels through the thalamus—located in the diencephalon. (Terlouw et al., 2016) The disruption of the reticular formation or the ARAS should result in immediate insensibility (Terlouw et al., 2016). The importance of the thalamus, specifically the central lateral thalamus, in maintaining sensibility was further described by Redinbaugh et al. (2020). In humans, Yeo et al. (2013) described the ARAS as responsible for maintaining sensibility. Wagner et al. (2019) observed that 293 cattle stunned with a pneumatic PCB were all rendered immediately insensible, but none had BD in the brainstem and Kline et al. (2019) also observed that all cattle in their study (45 of the 45) were rendered immediately insensible but did not observe any damage to the brainstem. Though the brainstem has been described as an important structure in stunning and euthanasia, it may not be critically important to induce insensibility. The brainstem also plays a critical role in cardiac and respiratory function (AVMA, 2020), so damage to the brainstem may be more important for euthanasia than stunning to prevent a return to sensibility.

Tissue damage to specific regions and structures of the brain can be observed in Tables 6 and 7 for sows and boars, respectively. Damage to the diencephalon was detected in 6 of the 10 (60.0%, 95% CI: 26.2% to 87.8%) sow heads that received the FRONTAL PCB application, 0 of 3 (0.0%, 95% CI: 0.0% to 70.8%) sow heads that received the TEMPORAL PCB application where the diencephalon could be observed on the split head, and 0 of 10 (0.0%, 95% CI: 0.0% to 30.8%), sow heads that received the BEHIND EAR PCB application. Damage to the diencephalon was detected in 2 of the 9 (22.2%, 95% CI: 2.8% to 60.0%) boar heads that received the FRONTAL PCB application, 0 of the 1 (0.0%, 95% CI: 0.0 5% to 97.5%) boar heads that received the TEMPORAL PCB application where the diencephalon could be observed on the split head, and 0 of the 11 (0.0%, 95% CI: 0.0% to 28.5%) boar heads that received the BEHIND EAR PCB placement. Damage to the brainstem was detected in 0 of the 10 (0.0%, 95% CI: 0.0% to 30.8%) sow heads that received the FRONTAL PCB placement and were not assessed for the TEMPORAL or BEHIND EAR placements. Damage to the brainstem was detected in 0 of the 9 (0.0%, 95% CI: 0.0% to 33.6%) boar heads that received the FRONTAL PCB placement and was not assessed for the TEMPORAL or BEHIND EAR placements. It is noteworthy that for all sow and boar heads included in the present study, no brainstem damage was observed with the FRONTAL placement, and brainstem damage could not be assessed for heads that received a TEMPORAL or BEHIND EAR PCB application because those regions of the brain could not be observed on the split TEMPORAL or BEHIND EAR heads. This is consistent with the findings of Anderson et al. (2021a) who did not observe brainstem damage in cadaver heads from sows and boars >200 kg that received a FRONTAL PCB application; brainstem damage was not assessed by Kramer et al. (2021). Kramer et al. (2022) reported that some brainstem TBI resulted from a PCB application in the frontal placement for sows and boars >200 kg, which is in contrast with our findings; however, the exact number of animals with brainstem damage was unclear. It should be noted that Kramer et al. (2022) used a different PCB device with a longer bolt travel distance than the one in the current study, or the pistol-type PCB used by Woods (2012), Anderson et al. (2019, 2021a), and Kramer et al. (2021).

Table 6.

Occurrence of damage to specific brain regions within cadaver heads from mature sows (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements¹ and sectioned by band saw following the plane of bolt entry

PCB placement		Brain structures
PCB placement		Frontal lobe	Parietal lobe	Temporal lobe	Occipital lobe	Corpus callosum	Diencephalon	Mesencephalon	Brainstem (pons and medulla)	Cerebellum
FRONTAL
	Proportion	0/10	10/10	—	8/10	9/10	6/10	1/10	0/10	1/10
	Percentage²	0.0	100.0	—	80.0	90.0	60.0	10.0	0.0	10.0
	95% CI³	0% to 30.8%	69.2% to 100.0%	—	44.4% to 97.5%	55.5% to 99.7%	26.2% to 87.8%	0.3% to 44.5%	0.0% to 30.8%	0.3% to 44.5%
TEMPORAL
	Proportion	—	9/9	3/3	—	3/3	0/3	—	—	—
	Percentage²	—	100.0	100.0	—	100.0	0.0	—	—	—
	95% CI³	—	66.4% to 100.0%	29.2% to 100.0%	—	29.2% to 100.0%	0.0% to 70.8%	—	—	—
BEHIND EAR
	Proportion	—	0/10	0/10	0/10	0/10	0/10	0/10	—	—
	Percentage²	—	0.0	0.0	0.0	0.0	0.0	0.0	—	—
	95% CI³	—	0.0% to 30.8%	0.0% to 30.8%	0.0% to 30.8%	0.0% to 30.8%	0.0% to 30.8%	0.0% to 30.8%	—	—

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²Statistical models to compare captive bolt placement effects would not converge due to the different regions of the brain which were accessible to the bolt path and exposed on the split head between PCB placements. As a result, 95% CIs were calculated and reported.

³95% Confidence interval for the percentage of brain damage.

Table 7.

Occurrence of damage to specific brain regions within cadaver heads from mature boars (BW < 200 kg) assigned to three penetrating captive bolt (PCB) placements¹ and sectioned by band saw following the plane of bolt entry

PCB placement		Brain structures
PCB placement		Frontal lobe	Parietal lobe	Temporal lobe	Occipital lobe	Corpus callosum	Diencephalon	Mesencephalon	Brainstem (pons and medulla)	Cerebellum
FRONTAL
	Proportion	0/9	8/9	—	8/9	7/9	2/9	0/9	0/9	3/9
	Percentage²	0.0	88.9	—	88.9	77.8	22.2	0.0	0.0	33.3
	95% CI³	0.0% to 33.6%	51.8% to 99.7%	—	51.8% to 99.7%	40.0% to 97.2%	2.8% to 60.0%	0% to 33.6%	0% to 33.6%	7.5% to 70.0%
TEMPORAL
	Proportion	—	7/10	1/1	—	1/1	0/1	—	—	—
	Percentage²	—	70.0	100.0	—	100.0	0.0	—	—	—
	95% CI³	—	34.8% to 93.3%	2.5% to 100.0%	—	2.5% to 100.0%	0% to 97.5%	—	—	—
BEHIND EAR
	Proportion	—	0/11	4/11	4/11	0/11	0/11	0/11	—	—
	Percentage²	—	0.0	36.4	36.4	0.0	0.0	0.0	—	—
	95% CI³	—	0.0% to 28.5%	10.9% to 69.2%	10.9% to 69.2%	0.0% to 28.5%	0.0% to 28.5%	0.0% to 28.5%	—	—

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³95% Confidence interval for the percentage of brain damage.

Relationship between extrinsic parameters and tissue thicknesses

Nonsignificant (P > 0.05) linear regression results can be observed in Tables 8 and 9 for sows and boars, respectively.

Table 8.

Linear regression relationships between source animal/head characteristics and tissue thicknesses for cadaver heads from sows < 200 kg BW assigned to three penetrating captive bolt (PCB) placements¹

PCB Placement	Variables (X;Y)	R ²	P-Value
FRONTAL
	Body weight, kg; soft tissue thickness, mm	0.0725	0.2520
	Body weight, kg; cranial thickness, mm	0.0011	0.9284
	Body weight, kg; total tissue thickness, mm	0.0002	0.9679
	Head weight, kg; soft tissue thickness, mm	0.0434	0.5637
	Distance between optic orbits, cm; soft tissue thickness, mm	0.0208	0.6911
	Distance between optic orbits, cm; cranial thickness, mm	0.2415	0.1492
	Distance between optic orbits, cm; total tissue thickness, mm	0.2522	0.1391
	Snout to poll distance, cm; soft tissue thickness, mm	0.1857	0.2138
	Snout to poll distance, cm; cranial thickness, mm	0.2179	0.1738
	Snout to poll distance, cm; total tissue thickness, mm	0.1784	0.2239
	Maximum deflection distance, cm; soft tissue thickness, mm	0.0021	0.9012
	Maximum deflection distance, cm; cranial thickness, mm	0.2983	0.1024
	Maximum deflection distance, cm; total tissue thickness, mm	0.3556	0.0688
TEMPORAL
	Body weight, kg; soft tissue thickness, mm	0.0532	0.5213
	Body weight, kg; cranial thickness, mm	0.0955	0.3848
	Body weight, kg; total tissue thickness, mm	0.0000	0.9893
	Head weight, kg; soft tissue thickness, mm	0.1289	0.3083
	Head weight, kg; cranial thickness, mm	0.0000	0.9996
	Head weight, kg; total tissue thickness, mm	0.3477	0.0728
	Distance between optic orbits, cm; soft tissue thickness, mm	0.1203	0.3262
	Distance between optic orbits, cm; cranial thickness, mm	0.0321	0.6206
	Snout to poll distance, cm; soft tissue thickness, mm	0.0264	0.6539
	Snout to poll distance, cm; cranial thickness, mm	0.0038	0.8650
	Snout to poll distance, cm; total tissue thickness, mm	0.0368	0.5955
	Maximum deflection distance, cm; soft tissue thickness, mm	0.0640	0.4809
	Maximum deflection distance, cm; cranial thickness, mm	0.0594	0.4974
	Maximum deflection distance, cm; total tissue thickness, mm	0.0145	0.7405
BEHIND EAR
	Body weight, kg; soft tissue thickness, mm	0.0138	0.7463
	Body weight, kg; cranial thickness, mm	0.1396	0.2876
	Body weight, kg; total tissue thickness, mm	0.0142	0.7432
	Head weight, kg; cranial thickness, mm	0.1384	0.2899
	Distance between optic orbits, cm; soft tissue thickness, mm	0.1015	0.3695
	Distance between optic orbits, cm; cranial thickness, mm	0.2589	0.1331
	Distance between optic orbits, cm; total tissue thickness, mm	0.3397	0.0770
	Snout to poll distance, cm; soft tissue thickness, mm	0.3576	0.0679
	Snout to poll distance, cm; cranial thickness, mm	0.0157	0.7303
	Snout to poll distance, cm; total tissue thickness, mm	0.3599	0.0667
	Maximum deflection distance, cm; soft tissue thickness, mm	0.0273	0.6481
	Maximum deflection distance, cm; cranial thickness, mm	0.0793	0.4305
	Maximum deflection distance, cm; total tissue thickness, mm	0.0979	0.3788

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¹Placements: FRONTAL—medial bolt entry approximately 3.5 cm superior to the optic orbits at midline perpendicular with the external surface of the head; TEMPORAL—bolt entry at the depression located between the right eye and right ear; BEHIND EAR—bolt entry directly caudal to the pinna of the ear on the same plane as the eyes and targeting the middle of the opposite eye.

BW, body weight.

Table 9.

Linear regression relationships between source animal/head characteristics and tissue thicknesses for cadaver heads from boars <200 kg BW assigned to three penetrating captive bolt (PCB) placements¹

PCB Placement	Variables (X;Y)	R ²	P-Value
FRONTAL
	Body weight, kg; soft tissue thickness, mm	0.0115	0.8009
	Body weight, kg; cranial thickness, mm	0.0575	0.5674
	Body weight, kg; total tissue thickness, mm	0.0929	0.4629
	Head weight, kg; soft tissue thickness, mm	0.1767	0.2997
	Distance between optic orbits, cm; soft tissue thickness, mm	0.2692	0.1876
	Snout to poll distance, cm; soft tissue thickness, mm	0.2608	0.1959
	Snout to poll distance, cm; cranial thickness, mm	0.1660	0.3163
	Snout to poll distance, cm; total tissue thickness, mm	0.0772	0.5053
	Maximum deflection distance, cm; soft tissue thickness, mm	0.1532	0.3377
TEMPORAL
	Body weight, kg; soft tissue thickness, mm	0.0503	0.5935
	Body weight, kg; cranial thickness, mm	0.4175	0.0835
	Body weight, kg; total tissue thickness, mm	0.1053	0.4328
	Head weight, kg; cranial thickness, mm	0.0121	0.7957
	Distance between optic orbits, cm; cranial thickness, mm	0.0229	0.7204
	Snout to poll distance, cm; cranial thickness, mm	0.2688	0.1880
	Snout to poll distance, cm; total tissue thickness, mm	0.0984	0.4492
	Maximum deflection distance, cm; cranial thickness, mm	0.0004	0.9646
BEHIND EAR
	Body weight, kg; soft tissue thickness, mm	0.0321	0.5979
	Body weight, kg; cranial thickness, mm	0.0002	0.9685
	Body weight, kg; total tissue thickness, mm	0.0376	0.5676
	Head weight, kg; soft tissue thickness, mm	0.0229	0.6566
	Head weight, kg; cranial thickness, mm	0.2605	0.1087
	Head weight, kg; total tissue thickness, mm	0.0187	0.6886
	Distance between optic orbits, cm; soft tissue thickness, mm	0.0568	0.4804
	Distance between optic orbits, cm; cranial thickness, mm	0.0151	0.7193
	Distance between optic orbits, cm; total tissue thickness, mm	0.0379	0.5661
	Snout to poll distance, cm; soft tissue thickness, mm	0.1170	0.3031
	Snout to poll distance, cm; total tissue thickness, mm	0.0000	0.9955
	Maximum deflection distance, cm; soft tissue thickness, mm	0.0111	0.7575
	Maximum deflection distance, cm; cranial thickness, mm	0.0000	0.9924
	Maximum deflection distance, cm; total tissue thickness, mm	0.0146	0.7232

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BW, body weight.

For sows, linear relationships were identified for head weight with the FRONTAL cranial thickness (Figure 6A) and total tissue thickness (Figure 6B) via simple linear regressions. These simple linear regressions were calculated to predict FRONTAL cranial thickness and total tissue thickness based on head weight. For each kg of head weight, the expected FRONTAL cranial thickness increased by 1.87 ± 0.44 mm (R² = 0.6916, P = 0.0029) and the expected FRONTAL total tissue thickness increased by 1.79 ± 0.38 mm (R² = 0.7336, P = 0.0016). For boars, linear relationships were identified for head weight with the FRONTAL cranial thickness (Figure 7A) and total tissue thickness (Figure 7B). For each kg of head weight, the expected FRONTAL cranial thickness increased by 1.90 ± 0.27 mm (R² = 0.8908, P = 0.0004) and the expected FRONTAL total tissue thickness increased by 1.64 ± 0.31 mm (R² = 0.8245, P = 0.0018). Anderson et al. (2021a) reported that head weight was a significant predictor of FRONTAL cranial thickness and FRONTAL total tissue thickness for cadaver heads from both sows and boars >200 kg BW. Hamilton et al. (2023) found that head weight was a significant predictor of soft tissue thickness, cranial thickness, and total tissue thickness in the FRONTAL PCB placement for physically castrated market barrows and immunocastrated boars.

Linear relationships were also identified for head weight with TEMPORAL soft tissue thickness (Figure 7C) and total tissue thickness (Figure 7D) for boars. For each kg of head weight, the expected TEMPORAL soft tissue increased by 1.31 ± 0.40 mm (R² = 0.6415, P = 0.0169) and the expected TEMPORAL total tissue thickness increased by 1.47 ± 0.32 mm (R² = 0.7760, P = 0.0011). Anderson et al. (2021a) reported that head weight was a significant predictor of total tissue thickness, but not soft tissue thickness, for the TEMPORAL PCB placement for boars >200 kg BW. Anderson et al. (2021a) also observed that head weight was a significant predictor of TEMPORAL soft tissue and total tissue thickness for sows >200 kg, which is in contrast with our findings. Linear relationships for sows were also identified for head weight with the BEHIND EAR soft tissue thickness (Figure 6C) and total tissue thickness (Figure 6D) via simple linear regressions. These simple linear regressions were calculated to predict BEHIND EAR soft tissue thickness and total tissue thickness based on head weight. For each kg of head weight, the expected BEHIND EAR soft tissue thickness increased by 1.88 ± 0.66 mm (R² = 0.5069, P = 0.0209) and the expected BEHIND EAR total tissue thickness increased by 2.55 ± 0.57 mm (R² = 0.7172, P = 0.0020). Anderson et al. (2021a) observed that head weight was a significant predictor of BEHIND EAR total tissue thickness, but not soft tissue thickness, for cadaver heads from sows >200 kg BW. Additionally, we did not observe that head weight was a significant predictor of BEHIND EAR cranial or total tissue thickness for boars, which is in contrast with the findings of Anderson et al. (2021a).

For sows, a linear relationship was identified for the distance between optic orbits and TEMPORAL total tissue thickness (Figure 8). For each cm of distance between optic orbits, the expected TEMPORAL total tissue thickness increased by 3.76 ± 1.04 mm (R² = 0.6181, P = 0.0070). For boars, a linear relationship was identified for distance between optic orbits and FRONTAL cranial thickness (Figure 9A) and total tissue thickness (Figure 9B). For each cm of distance between optic orbits, the expected FRONTAL cranial thickness increased by 4.71 ± 1.15 mm (R² = 0.7251, P = 0.0065) and the expected FRONTAL total tissue thickness increased by 3.82 ± 1.26 mm (R² = 0.6042, P = 0.0232). Linear relationships for boars were also identified for the distance between optic orbits and TEMPORAL soft tissue thickness (Figure 9C) and total tissue thickness (Figure 9D). For each cm of distance between optic orbits, the expected TEMPORAL soft tissue thickness increased by 4.91 ± 1.17 mm (R² = 0.7433, P = 0.0059) and the expected TEMPORAL total tissue thickness increased by 4.17 ± 1.64 mm (R² = 0.5192, P = 0.0437). To the best of our knowledge, this is the first study to evaluate the relationship between distance between optic orbits and tissue depth parameters for swine.

Figure 9. — Relationship of tissue thickness measurements, mm and distance between optic orbits, cm of cadaver heads from boars < 200 kg body weight. A—FRONTAL cranial thickness (n = 8); B—FRONTAL total tissue thickness (n = 8); C—TEMPORAL soft tissue thickness (n = 8); D—TEMPORAL total tissue thickness (n = 8).

A linear relationship was identified for snout-to-poll distance and TEMPORAL soft tissue thickness for boars (Figure 10A). For each cm of snout to poll distance, the expected TEMPORAL soft tissue thickness increased by 2.49 ± 0.86 mm (R² = 0.5828, P = 0.0275). Significant linear relationships were not observed between snout-to-poll distance and TEMPORAL cranial thickness (R² = 0.2688, P = 0.1880) or TEMPORAL total tissue thickness (R² = 0.0984, P = 0.4492). A significant linear relationship was observed between snout-to-poll distance and BEHIND EAR cranial thickness (Figure 10B). For each cm of snout to poll distance, the expected BEHIND EAR cranial thickness decreased by 1.83 ± 0.73 mm (R² = 0.4140, P = 0.0327). To the best of our knowledge, this is the first study to evaluate the relationship between snout-to-poll distance and tissue depth parameters for swine.

For boars, a linear relationship was identified for maximum deflection distance and FRONTAL cranial thickness (Figure 11A) and total tissue thickness (Figure 11B). For each cm of maximum deflection distance, the expected FRONTAL cranial thickness increased by 8.08 ± 1.79 mm (R² = 0.7722, P = 0.0041) and the expected FRONTAL total tissue thickness increased by 6.96 ± 1.80 mm (R² = 0.7147, P = 0.0082). Woods (2012) et al. reported difficulties euthanizing sows and boars >200 kg that did not have a “plank” face shape with a pistol-type PCB, suggesting that the shape of the face may be related to the distance the bolt must travel to reach the brain. Our findings corroborate this concept and further suggest that the frontal profile of the head (i.e., face shape) and tissue thickness may be related. It should also be noted that we did not observe a significant relationship between maximum deflection distance and FRONTAL cranial or total tissue thickness, which is in contrast with the findings of Anderson et al. (2021a). Hamilton et al. (2023) found that maximum deflection distance was a significant predictor of cranial thickness in the frontal placement for physically castrated market barrows, but not for immunocastrated boars.

Linear relationships were also identified for boars between maximum deflection distance and TEMPORAL soft tissue thickness (Figure 11C) and total tissue thickness (Figure 11D). For each cm of maximum deflection distance, the expected TEMPORAL soft tissue thickness increased by 7.35 ± 1.81 mm (R² = 0.7336, P = 0.0066) and the expected TEMPORAL total tissue thickness increased by 7.21 ± 2.00 mm (R² = 0.6839, P = 0.0113). However, Hamilton et al. (2023) evaluated the relationship between maximum deflection distance and FRONTAL tissue depth parameters for physically castrated market barrows and immunocastrated boars and found that maximum deflection distance was a significant predictor of FRONTAL cranial thickness for physically castrated market barrows, but not for immunocastrated boars.

Our results suggest that the FRONTAL PCB placement may provide a path with less tissue for the bolt to travel through than either the TEMPORAL or BEHIND EAR PCB placements for sows and boars weighing <200 kg. Additionally, the expansive sinus cavities that are typical of mature sows and boars (EFSA, 2004; Woods et al., 2010; HSA, 2016; NPB and AASV, 2016; Anderson et al., 2021a) were observed in all cadaver heads in this study. As described by Anderson et al. (2021), the use of cadaver heads prevents drawing conclusions directly related to the efficacy of a PCB placement. These findings should be used to inform future research related to PCB placement and PCB device selection for mature sows and boars.

It is important to recognize that only one type of PCB, with a single bolt length and powder cartridge combination, was used in this study. There are a variety of commercially available PCB devices of both the pistol and inline varieties, which have differences in potential bolt travel distances and thus the ability of the bolt to reach the brain and cause damage consistently (described by Anderson et al., 2022). Another limitation of the present study is that BD was visually assessed from images of each head and TBI or hemorrhage scoring was not conducted. TBI or hemorrhage scoring systems, such as those used by Millar and Mills (2000), Woods (2012), and Kramer et al. (2021) could not be reliably used because whole, intact brains were not available for assessment and cadaver heads were sourced from animals which were exsanguinated completely, leaving no available blood supply. Lastly, the comparison of BD between all regions and structures of the brain could not be made between PCB placements due to the different regions and structures that were visible given the split associated with each PCB placement.

All PCB shots were applied under highly controlled laboratory conditions by a single operator in this study. PCB use under field conditions, either on-farm or in slaughter establishments, would not allow for the same level of accuracy or precision with placement. As a result, the larger brain area and target area of the FRONTAL PCB placement may be advantageous.

To the best of our knowledge, this study was the first to assess PCB use for sows and boars <200 kg BW. It is important to recognize that in our study, and others evaluating PCB use for mature breeding swine (Anderson et al., 2021a; Kramer et al., 2021), BW has been the primary inclusion criteria and animal age has not been reported. It is possible that either age or the onset of puberty is responsible for the thickening of the cranium and expansion of the sinus cavities observed in breeding swine compared to market hogs and further investigation of this relationship is warranted and necessary.

Implications

This study was intended to serve as an initial step in the scientific evaluation of PCB use for sows and boars weighing <200 kg BW. Of the three PCB placements evaluated, the FRONTAL placement appeared to be more reliable in reaching the brain than the TEMPORAL or BEHIND EAR placements. The reliability of the FRONTAL placement over the TEMPORAL and BEHIND EAR placements was indicated by the least tissue for the bolt to travel through to reach the brain, the greatest potential target area, and a high prevalence of BD. Further studies on the TEMPORAL and BEHIND EAR PCB placements are warranted, as are studies related to the capacity of various PCB devices to reach and disrupt the brain. We found that the PCB device used in this study may not have the capacity to consistently reach the brain, depending on the placement. Ultimately, at this time the FRONTAL PCB placement may present the least risk of failure for the PCB euthanasia of sows and boars <200 kg BW with the PCB device used in this study.

Acknowledgments

We thank the commercial slaughter establishment that provided the cadaver heads for this research. We greatly appreciated the data collection assistance of O. Barber, M. Cowell, B. Dittrich, L. Geist, E. Hamilton, R. Heap, E. Hensman, A. Kinnaird, K. Kirk, A. Matzek, H. Olsen, B. Plazcz, M. Redmann, M. Seehusen, S. Sigl, L. Streich, A. Tomandl, and G. Wellnitz, (all affiliated with the University of Wisconsin—River Falls at the time of this study). We appreciated the space and accommodations provided by the University of Wisconsin—River Falls Meat Lab and manager R. Rehnelt. The authors also appreciated assistance from A. Rendahl with upper reference limit calculations. The provision of captive bolt stunning equipment by Jarvis Corporation and technical support by Bunzl Processor Division was greatly appreciated. We would also like to thank the commercial meat processing company that provided the bandsaw used for this research. This work was supported by the Agriculture and Food Research Initiative competitive award no. 2022-67016-36344 from the USDA National Institute of Food and Agriculture.

Glossary

Abbreviations

BD: brain damage
BW: body weight
CI: confidence interval
HCW: hot carcass weight
PCB: penetrating captive bolt
TBI: traumatic brain injury
URL: upper reference limit (97.5% reference interval)
URL 90% CI: the 90% confidence interval of the upper reference limit

Contributor Information

Karly N Anderson, Department of Animal Science, University of Nebraska – Lincoln, Lincoln, NE 68583, USA.

Ashlynn A Kirk, Department of Animal and Food Science, University of Wisconsin – River Falls, River Falls, WI 54022, USA.

Jennifer Berger, Abbyland Pork Pack, Curtiss, WI 54422, USA.

Arquimides A Reyes, Department of Animal and Food Science, University of Wisconsin – River Falls, River Falls, WI 54022, USA.

Ruth Woiwode, Department of Animal Science, University of Nebraska – Lincoln, Lincoln, NE 68583, USA.

Perle E Zhitnitskiy, Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108, USA.

Kurt D Vogel, Department of Animal and Food Science, University of Wisconsin – River Falls, River Falls, WI 54022, USA.

Conflict of Interest Statement

The authors declare no real or perceived conflicts of interest.

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PERMALINK

Relationship of tissue dimensions and three captive bolt application sites on cadaver heads from mature swine (Sus scrofa domesticus) <200 kg body weight

Karly N Anderson

Ashlynn A Kirk

Jennifer Berger

Arquimides A Reyes

Ruth Woiwode

Perle E Zhitnitskiy

Kurt D Vogel

Abstract

Introduction

Materials and Methods

Animal use protocol

Description of cadaver heads

Table 1.

Description of captive bolt tool, placement, and treatment assignment

Figure 1.

Post-application head processing and measurements

Figure 2.

Figure 3.

Figure 4.

BD assessment

External head measurements

Statistical analyses

Results and Discussion

Source animal and cadaver head characteristics

Tissue and cranial measurements

Table 2.

Table 3.

Figure 5.

Brain tissue damage assessment

Table 4.

Table 5.

Table 6.

Table 7.

Relationship between extrinsic parameters and tissue thicknesses

Table 8.

Table 9.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

Figure 11.

Implications

Acknowledgments

Glossary

Abbreviations

Contributor Information

Conflict of Interest Statement

Literature Cited

ACTIONS

PERMALINK

RESOURCES

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