Investigations of tissue dimensions and captive bolt application on swine cadaver heads – 2020 Badger Swine Symposium

Karly Anderson  00:00

Hi everyone. My name is Karly Anderson and I’m currently a master’s student in the Department of Animal and Dairy Sciences at the University of Wisconsin-Madison, and I’m also the animal welfare lab coordinator at the University of Wisconsin-River Falls. Today I’ll be discussing preliminary findings from our project titled “Foundational investigations of tissue dimensions and their relation to captive bolt application sites on cadaver heads for mature swine”.

Karly Anderson  00:25

So before I begin discussing our findings, I’d like to give a little overview of the project. But first, I would like to acknowledge my co-investigators Dr. Alex Ramirez, Dr. Jim Claus, Dr. Madonna Benjamin, Dr. Angela Baysinger, Dr. Brett O’Brien, Dr. Arquimedes Reyes, and Dr. Kurt Vogel. And I’d also like to thank the National Pork Board for funding this research and for all of the undergraduate research assistants in the UW-River Falls animal welfare lab for their time and assistance with this project.

Karly Anderson  00:57

A little bit of background regarding captive bolt euthanasia, penetrating captive bolt is an approved method of euthanasia by both the American Veterinary Medical Association or the AVMA, and the National Pork Board for the euthanasia of swine. The frontal location is approved by both the AVMA and the National Pork Board and is the most common application site. However, the AVMA has identified two other possible sites: the temporal location, which is shown in figure 12 on the left hand side, in the upper image, and the behind the ear toward the opposite eye, which is shown by figure 12 on the right hand side here in the bottom image. Now, these were from the 2013 AVMA euthanasia guidelines. After this project had already been started an update to these guidelines was made for 2020. And that update stated that only the frontal location is approved for use with captive bolt, but all three locations the temporal behind the ear and the frontal site may be used with gunshot and you can see the updated figure for the 2020 euthanasia guidelines on the right as well.

Karly Anderson  02:07

Very few studies have been published related to the captive bolt euthanasia of swine. Specifically, this method has not yet been validated for sows and boars, despite being used every day in the industry successfully.

Karly Anderson  02:20

It is also difficult and not advised to perform captive bolt euthanasia on a pig that is not restrained and behind the ear and temporal locations may serve as alternative locations for euthanasia of large sows and boars. However, validation for these alternative locations is required.

Karly Anderson  02:37

Peer-reviewed, published data to validate either the either of the alternate locations, the temporal or the behind the ear locations did not appear to exist at the time of this study. As such, this study was then designed as the first step in scientifically validating the behind the ear and the temporal locations for large sows and boars.

Karly Anderson  02:56

The captive bolt used for this project was a Jarvis model PAS which means it’s a pistol-type captive bolt, and we used the long stunning rod nosepiece assembly and we used Jarvis orange powder cartridges. The nosepiece assembly and powder cartridges were selected based on manufacturer recommendations.

Karly Anderson  03:15

Our objectives were to determine the tissue depth cross-sectional brain area regions, regions of brain damage and bolt to brain contact that is associated with the frontal, temporal, and the behind the ear shot locations for the euthanasia of swine via penetrating capture bolt on sow and boar heads. Because this is a preliminary report, we will only focus on the tissue depths and cross sectional brain areas.

Karly Anderson  03:41

I would now like to discuss the methods and data collection that we used for this project. So as I mentioned, we had three captive bolt placements: the frontal, caudal to pinna, or behind the ear, and the temporal. The frontal shot was placed 3.5 centimeters superior to a line drawn across the top of the eyes at the midline. And this can be seen in the far left image on the bottom of the screen. The caudal to pinna, or behind the ear shot, was placed directly caudal to the pinna of the right ear on the same plane as the eyes and targeted at the middle of the opposite eye. This can be seen in the middle image on the bottom of the screen.  The temporal location was placed at the depression posterior to the lateral canthus, or the outer corner of the eye, within the plane between the lateral canthus and the base of the ear, and that can be seen at the far right image on the bottom of the screen.

Karly Anderson  04:33

For this project, we obtained 157 cadaver heads from sows and boars that were commercially slaughtered at a processing facility under federal law. The average weight of the source pigs was 231 kilograms.  All heads had skin-on and intact jowls.  Approximately 6 centimeter of neck was left behind the ear to prevent tissue distortion. Specifically with that behind the ear shot. All heads were cooled for approximately 64 hours prior to processing. And this is to make the brain tissue easier to see once the heads were split.

Karly Anderson  05:09

All measurements were taken from images collected at the time of head processing. So on this slide, I’ll walk through what the thickness measurements we took were.  We measured soft tissue thickness, which referred to the tissue from the application site to the exterior surface of the cranium. We also collected cranial thickness, which was the thickness from the external exterior surface of the cranium to the interior surface of the cranium along the bolt path. And then we measured total tissue thickness by combining soft tissue and cranial thicknesses. And this was the total soft tissue and cranial thickness from the site of application to the interior surface of the cranium along the bolt path.

Karly Anderson  05:47

And on the right I’ve included an image of a split temporal shot, a split frontal shot and a split behind the ear shot, just so you can all get a picture of what these heads might look like.

Karly Anderson  06:00

We then measured brain area from the same image collected at the head of time processing and an online irregular area calculator was used to calculate the cross sectional surface area of the exposed brain within the plane of bolt travel. We used the same online irregular area calculator for all tissue thickness measurements.

Karly Anderson  06:23

All statistical analyses were performed in the SAS Enterprise Guide 7.1 environment.  Analyses conducted on tissue measurements and brain area use the students T-test with two key test adjustments specified within the model. All differences were considered significant when alpha was less than or equal to 0.05.

Karly Anderson  06:46

I’d now like to discuss the preliminary findings from this project.  I’ll walk through a series of tables and graphs and discuss exactly what we found. And then we’ll walk through what these results actually mean following that. So this graph includes data regarding tissue parameters from our cadaver heads of both mature sows and boars. And these are just looking at the tissue thicknesses. So in orange, we have soft tissue thickness, in yellow, we have cranial thickness, and in green, we have the total tissue thickness.

Karly Anderson  07:17

Soft tissue thickness was greatest in the behind the ear location, followed by the temporal location and was the least in the frontal location. Cranial thickness then was greatest in the frontal location, followed by the behind the ear location, and was the least in the temporal location. Total tissue thickness was greatest in the behind the ear location, followed by the temporal location, followed by the frontal location. All tissue thicknesses were significantly different across each treatment for all sows and boars.

Karly Anderson  07:48

In this table, you can see the specific values of soft tissue thickness, cranial thickness, total tissue thickness, as well as cross sectional brain area for all sows and boars. Any superscripts that differ within a line identify significant differences between means within those dependent variables. Soft tissue thickness was greatest in the behind the ear location with a mean of 54.3 millimeters, followed by the temporal location with a mean of 45.6 millimeters, followed by the frontal location with a mean of 13.4 millimeters. All of these were significantly different.

Karly Anderson  08:31

The cranial thickness then was greatest in the frontal location with a mean of 41.0 millimeters, followed by the behind the ear location with a mean of 30.9 millimeters, followed by the temporal location with a mean of 18.8 millimeters. Again, all of these were significantly different. The total tissue thickness then was greatest in the behind the ear location, followed by the temporal location, followed by the frontal location. These were once again significantly different.

Karly Anderson  08:59

Cross-sectional brain area then which tells us our, the area we have as a target, was greatest in the frontal location with a mean of 4,270.5 millimeters squared, followed by the behind the ear location with a mean of 2,617.5 millimeters squared, followed by the temporal location with a mean of 1,603.1 millimeters squared.

Karly Anderson  09:29

This graph then shows the preliminary data regarding tissue parameters of cadaver heads from only mature sows. So our soft tissue thickness is once again in orange, our cranial thicknesses again in yellow, and our total tissue thickness again is in green.

Karly Anderson  09:46

So four sows only, the behind the ear shot location had the thickest, soft tissue, followed by the temporal location and then the frontal location had the least amount of soft tissue thickness. The frontal location for sows had the greatest cranial thickness, followed by the behind the ear location, followed by the temporal location. The total tissue thickness was greatest for sows in the behind the ear location, followed by the temporal location, followed by the frontal location. All tissue thicknesses were significantly different across the three treatments for sows.

Karly Anderson  10:25

In this table, I’ll walk through what those specific tissue thicknesses were, as well as discussed cross-sectional brain area for sows only. Soft tissue thickness was greatest in the behind the ear location with a mean of 53.8 millimeters, followed by the temporal location with a mean of 45.93 millimeters, followed by the frontal location with a mean of 13.9 millimeters. Cranial thickness then was greatest in the frontal location with a mean of 47.1 millimeters, followed by the behind the ear location with a mean of 30.2 millimeters and then followed by the temporal location with a mean of 17.6 millimeters.

Karly Anderson  11:05

Total tissue thickness then was greatest in the behind the ear location, followed by the temporal location followed by the frontal location. Cross-sectional brain area, which again tells us our target area was greatest in the frontal location with a mean of 4509 millimeters squared, followed by the behind the ear location with a mean of 2,767.5 millimeters squared, followed by the temporal location with a mean of 1,964.4 millimeters squared. Again, all of these thicknesses and brain areas were significantly different across treatments.

Karly Anderson  11:49

This table then looks at the tissue thicknesses for boars only.  Again, soft tissue thickness is shown in orange, cranial thickness is shown in yellow, and total tissue thickness is shown in green. For boars soft tissue thickness was greatest and then behind the ear location, followed by the temporal location followed by the frontal location. Cranial thickness for boars was greatest in the frontal location, followed by the behind the ear location, followed by the temporal location.

Karly Anderson  12:21

I’d like to take a moment to point out though, that for boars only the frontal cranial thickness did not differ from the behind the ear cranial thickness, only the frontal and temporal cranial thicknesses were significantly different. Total tissue thickness then was greatest in the behind the ear location for boars, followed by the temporal location followed by the frontal location.  All soft tissue and total tissue thicknesses were significantly different.

Karly Anderson  12:52

This table walks through the specific values for the boars only. Soft tissue thickness was greatest in the behind the ear location with a mean of 54.7 millimeters, followed by the temporal location with a mean of 45.3 millimeters, followed by the frontal location with a mean of 12.9 millimeters.

Karly Anderson  13:10

Cranial thickness was greatest in the frontal location with a mean of 34.8 millimeters, followed by the behind the ear location with a mean of 31.7 millimeters, followed by the temporal location but the mean of 22.1 millimeters. Now with the cranial thickness, I’d like to reiterate that only the frontal and temporal cranial thicknesses were significantly different from one another.  They did not differ significantly from the behind the ear location. Total tissue thickness for boars was greatest and they behind the ear location, followed by the temporal location, followed by the frontal location. Cross-sectional brain area for boars was greatest in the frontal location with a mean of 4,031.9 millimeters squared. This was followed by the behind the ear location with a mean of 2,467.5 millimeters squared, followed by the temporal location with a mean of 1,241.8 millimeters squared.

Karly Anderson  14:13

Now this graph shows a comparison of the brain areas across all of our heads. So in orange we have brain areas from sows and boars combined, in yellow is brain areas from sows only, and then green we have brain areas from boars only. All brain areas across treatments were significantly different. In all cases, the brain area was greatest in the frontal location, followed by the behind the ear location and brain area was was the smallest in our temporal heads.

Karly Anderson  14:48

I now would like to have a discussion on what this preliminary data suggests and what the implications from this work are. The frontal placement appears to have the greatest likelihood for successful euthanasia of large sows and boars. From our findings, we know that the frontal location consistently has the least total tissue thickness, as well as the greatest cross-sectional brain area.

Karly Anderson  15:13

That means that there is the least amount of tissue for the captive bolt to have to travel through, as well as the largest target area. So, that being said, future research should work to refine captive bolt tools to ensure adequate reach, so sufficient reach from the bolt to reach the brain. As well as continue the validation process for the behind the ear and temporal placements. The validation process for the behind the ear and temporal placement should be continued as it’s important to have an alternate location and times when you cannot access the frontal location.

Karly Anderson  15:48

Additionally, at this time, it appears that the behind the ear location has a greater target area, but also has more tissue to travel through, while the temporal location has a smaller target area, but there’s less tissue to travel through then with the behind the ear location. So the frontal placement may present less risk than the alternate behind the ear or temporal placements for the capital bolt euthanasia of large sows and boars at this time.

Karly Anderson  16:17

If you have any questions, please feel free to reach out to me via email. I’ve included my email address and the bottom left hand corner of this screen. These are the works that have been cited throughout this presentation and I’d like to thank you all for your time today.