Skip to content

Other Resources

Ep. 082: Understanding How Horses Eat and Its Impact on Dental Health with Dr. Stephanie Bonin

Co-hosts Dr. Tania Cubitt and Katy Starr chat with Dr. Stephanie Bonin, a principal and senior biomechanical engineer, about her research on how horses chew and how certain feeds impact dental management needs.

Episode Notes

On this episode, co-hosts Dr. Tania Cubitt and Katy Starr chat with Dr. Stephanie Bonin, a principal and senior biomechanical engineer, about her research on the movement of how horses chew and why it matters, including:

  • How horses chew long-stem hay or grass versus smaller pelleted feeds and forage
  • How the height at which horses eat can affect their jaw movement and teeth alignment
  • Potential dental management needs depending on the horse’s diet

For our more advanced horse owners and those asking for a deeper dive into the science – THIS episode is for you! See the notes below for a brief glossary on some terms discussed in this episode.


Have a topic idea or feedback to share? We want to connect with you! Email


Episode References:

~8:54 – Dr. Bonin’s image description in episode of the McPhail Equine Performance Center set-up with Dr. Hilary Clayton -

~12:02 - Kinematics of the equine temporomandibular joint -

~27:49 - Comparison of mandibular motion in horses chewing hay and pellets -


Glossary of Terms:

  • ~9:55 – Retroreflective makers – reflect light back in the direction it came, in this scenario, to the cameras
  • ~11:39 – TMJ - Temporomandibular joint
  • ~12:24 – Mandible – lower jaw, Maxilla – upper jaw
  • ~13:01 – Caudally – in the direction of or situated in or near the tail or posterior part of the body
  • ~13:05 – Kinematics – the study of motion without referencing any force that may actually cause the motion – how they’re moving, not why they’re moving, e.g. distance or displacement, speed or velocity, and acceleration.
  • ~17:26 – Adbraded down – worn down
  • ~17:32 – Atlanto-Occipital Joint – the poll of the horse which connects the first vertebrae with the skull
  • ~19:47 – Ramus – the large bone of the mandible or lower jaw
  • ~36:32 – Malocclusions – the misalignment between a horse’s upper and lower jaws
  • ~42:00 – Lateral excursion– the side-to-side movement of the lower jaw away from the midline


Helpful Standlee Products:


Stay connected with Dr. Stephanie Bonin:


*Views and opinions expressed by guests are their own and do not necessarily reflect the view of Standlee Premium Products, LLC.*


Katy Starr (00:01):

Hi, I'm Katy.


Dr. Tania Cubitt (00:02):

And I'm Dr. Cubitt. We're going Beyond the Barn. Come join us on this journey as we bust equine and livestock nutrition myths and interview some of the most intriguing experts in the country.


Katy Starr (00:15):

We'll go behind the scenes of how premium western quality forage is grown and brought to your favorite farm and ranch retail store. We're so glad you're here. Welcome back to another episode of Beyond the Barn, Dr. Cubitt, it's great to have you here with us today.


Dr. Tania Cubitt (00:34):

I'm excited to be back and I'm excited for our guest today.


Katy Starr (00:37):

Yes, we have a fantastic guest joining us and to give you a little bit of insight, our next guest is a principal and senior biomechanical engineer, where she analyzes injuries involving automobile collisions, pedestrian and cyclist collisions, helmet protection, slip and falls, sports related injuries, and equestrian and workplace accidents. For her master's thesis, she quantified the equine temporal mandibular joint movement while chewing. She is the chair of the ASTM Equestrian Helmet Committee, where she leads the committee towards evidence-based improvements to the ASTMF 1163 Equestrian Helmet Standard. She is also a lifelong equestrian. We'd like to welcome Dr. Stephanie Bonin to the Beyond the Barn podcast. Thanks for being here with us today, Dr. Bonin.


Dr. Stephanie Bonin, PhD, PE (01:29):

Good morning. Thank you for having me.


Katy Starr (01:31):

Yes, we are so excited to talk to you today about how horses eat. You've done a lot of research in that area in your early time and it's going to be a great topic for today. And so, before we get started on our topic, I would like to remind our listeners that any of the topics we cover on the Beyond the Barn podcast are more generalized and not specific to any individual horse or any specific situation. So, be sure to always work with your veterinarian and nutritionist before making any drastic changes to your horse's feed program. Or you can reach out directly to talk to Dr. Cubitt or Dr. Duren on any specifics that you would like to know. So, Dr. Bonin, can you just first off, maybe, tell us a little bit about your background with horses and where you grew up?


Dr. Stephanie Bonin, PhD, PE (02:18):

Sure, yep. I grew up in Michigan. I started taking weekly lessons at the local stable. My parents tell me that it was, sort of, a reward for me finally grabbing onto something that I wanted to read all the time. I wanted to read about horses. So, the reward for that was, "Oh, we'll take you to the stables.", and you know, that was the beginning of the end of being hooked on all things horses. So, I spent all my formative years at the barn. Entire summers spent there riding. As a lot of young girls do, I started in the hunter jumper discipline, moved into eventing as a teen, and would follow vets around, always assisting when I could. As I was moving into my later teen years, I was a, you know, working student for various trainers in different locations. Ended up in a university and with my head in a book for many hours, for many years. So, that sort of, you know, got in the way of the riding passion. But you know, I still ride today, still compete. So, yeah, that's my true passion.


Katy Starr (03:18):

Yeah, that's excellent. And I think you kind of touched on it, but you spent quite a few years with various trainers. You had mentioned to me, in the U.S., England, and Germany. Could you maybe share a little bit more about that experience? That's kind of neat that you got to go beyond just the United States.


Dr. Stephanie Bonin, PhD, PE (03:37):

Yeah, well, and it really, if you want to learn work ethic, boy, be a working student, really for a professional competitor. So, when I was 15, I lived in Pennsylvania, and I lived with Jane Sleeper in her apartment, and I was her working student. She's an event rider, she was in the Seoul Games. So, this was a long time ago, but I really learned what hard work is all about and learned a lot of grit and just general skills in maintaining athletes, you know, maintaining their horses and the care and the follow up that needs to go on with them post, you know, during competition, post competition. Then I was a working student in Maryland for more of a local trainer. It was a family connection or through my sister, it was an area near her. I think the following year I was in Germany, that was training with an event coach, Colonel von Ziegner. His primary focus is dressage, and so, he had done a lot of clinics in Texas and Michigan and other locations. My trainer was German, so she put me in touch with her. So, I got to stay with that family. And then the following year it was in England and this was David O'Connor. He and Karen were based in England at that time. And so, got to explore England and the other parts of Europe during that time. But yeah, again, being a, you know, working student under those sorts of circumstances, you learn a lot and you learn how to be efficient and effective ,


Dr. Tania Cubitt (05:01):

Which probably held you in good stead for coming back and doing your PhD.


Dr. Stephanie Bonin, PhD, PE (05:04):

You what? That's true. .


Dr. Tania Cubitt (05:06):

It's exactly what you needed.


Dr. Stephanie Bonin, PhD, PE (05:06):

That's a good point. Yeah.


Dr. Tania Cubitt (05:08):

I always say to people, you don't have to be the brightest person to get through a PhD, but you've got to know how to work.


Dr. Stephanie Bonin, PhD, PE (05:13):

Yes, that's true. I think that your tenacity and your grit take you much further. You need that first and foremost, before you can complement that with your learning ability. So.


Katy Starr (05:22):

That's such a cool opportunity for you though, to be able to do so many of those things. That's really neat. So, we're going to be talking mainly about some of your early research today, just as Dr. Cubitt and I were talking before about just how fascinating and interesting and well-rounded you are in the things that you do and have done. So, could you talk a little bit about your current role and how that has transitioned over time?


Dr. Stephanie Bonin, PhD, PE (05:47):

Sure. So currently, I work at a forensic consulting firm and we get hired mostly by attorneys and we're brought into cases where there's a litigation. Let's say someone's in a car accident and they're suing the person that struck them. And so, our firm, we reconstruct the collision and we used, you know, sort of like the damage profile that we see on the vehicle. Crash test data. We determine with some physics-based software, how the collision took place. And then my role in biomechanics is once we know what happened to the vehicle, I then determine what happened to the people inside and do their injuries make sense, you know, what was their, we call it exposure? What did they experience during that crash and how does that compare with the tissue that was injured? So, motor vehicle crashes are what we mostly do as a company.


Dr. Stephanie Bonin, PhD, PE (06:38):

There's also, you know, the pedestrian impacts, cyclist impacts. We have lane splitting in California, so we have a lot of motorcyclists that end up on the roadway. And my PhD work was focused on helmet protection, so head injuries and helmet protection. So, I tend to do a lot of work related to that for cyclists, motorcyclists, equestrians, motocross, a variety of different helmet types in terms of, you know, was the helmet effective? Was there something wrong with the helmet? Were they wearing it properly? What would the outcome be, had they been wearing a different helmet? Let's say they were wearing something that was not appropriate, and so, that's what I'm doing now and it, you know, in terms of how that evolved from my more equestrian focused work back, you know, in my undergrad, so in my undergrad and in my master's, all of the projects that I could do focused on somehow equine.


Dr. Stephanie Bonin, PhD, PE (07:31):

So, I looked at the strain patterns of horses' hooves during, with different trimming style, different trimming techniques, you know, what does the strain pattern look like on the surface of the hoof and different shoeing techniques, or you know, for one of my engineering classes, I wanted to look at the heat transfer problem of the deep digital flexor tendon, for example. So, I did a little simulation with that. And then, of course, the research with the TMJ is part of my master's. So, the master's work was performed at, we call it a gait lab. So, gait as in G-A-I-T, as in how you move. And I had done some work in the human domain, so looking at how humans move. Their performance mostly for, you know, how people, for example, maybe they depart out of starting blocks or how they might swing their golf club. But the lab that I worked in focused on kids with CP, cerebral palsy. So, it was evaluating their movements pre and then potentially the techniques that you use in those gait labs translates into horses. So, the McPhail Equine Performance Center is a large, like an oversized version of a gait lab, where we can measure very specific movements of the horse. Usually, it's related to different gaits. But you can also look at the TMJ.


Dr. Tania Cubitt (08:46):

And I guess, at that time, you were working with one of the world's leading experts on gait analysis, Dr. Clayton.


Dr. Stephanie Bonin, PhD, PE (08:53):

Yes, yes. Hillary Clayton was running this equine performance center at the time. So, yeah, what we're looking at on this image here, there's a horse in the middle of the space, and we actually have force plates under there, which are like large scales. They can tell you how much force is being applied forward, backwards, side to side, and up and down. So, you know, the three directions and then the cameras that surround the space are able to detect markers that we place on the surface of the horse. So, you place these markers at locations where as they're moving, you can then relate one bony segment, we'll call it. So, you know one, you know, let's say maybe the cannon bone relative to the fetlock, for example. You want to be able to look at the movement of one body segment relative to the other.


Dr. Stephanie Bonin, PhD, PE (09:39):

You can do that in three space as well. A setup like this allows you to track these markers as a horse is passing through the space. For the work I did, of course, they didn't need to move, they just needed to stand there and chew. But that was the principle in terms of being able to use these, we call them retro reflective markers, meaning they reflect light back to the cameras. And then after you calibrate the space, you need to know where all of these markers are in space. You can then figure out with a bunch of equations, how one segment moves relative to another.


Katy Starr (10:07):

And for those that are listening to this in audio, we'll be sure to link that in our show notes and when you have a moment you can jump in there and take a look at what Dr. Bonin was describing there. That's really interesting. I wanted to ask you a little bit about your time. You were working on some of this research, your early research. You had mentioned to me originally that you had kind of had a mentor, a veterinarian that kind of inspired you to do some of this initial research. Can you talk about that a little bit?


Dr. Stephanie Bonin, PhD, PE (10:37):

Yes. Tom Johnson, he's one of the authors, at least on I think maybe both of the papers. So, he was one of the vets that I would follow around as a kid, at the barn then, you know, as you go through life. And there was never any reason to really stay in touch. But then, when this research project came up, he became involved because he moved into a dentistry practice. So, rather than being a general practitioner. And he moved into an equine dentistry, so he was part of it as the clinician, but also, he ensured that in the beginning of our study we wanted to make sure that there were no issues from a dental perspective, you know, they had sort of, you know, clearance to be able to participate in this particular study. So, yeah, years later your childhood connections or relations come, they, you know, can come back.


Katy Starr (11:22):

See, networking. It starts even in the early years. Right, ?


Dr. Stephanie Bonin, PhD, PE (11:26):



Katy Starr (11:27):

That is so funny.


Dr. Stephanie Bonin, PhD, PE (11:28):



Katy Starr (11:29):

Okay, so why don't we go ahead and get into talking about, we have a couple of studies that we wanted to discuss today. And I will also say when we talk about, you had mentioned TMJ earlier in the conversation, so when you hear that, when our listeners hear that today, to know that that's the temporomandibular joint, right? So, that's the shortened acronym for that. I just want to make sure that everybody, when Dr. Bonin is talking about that today, that's what she'll be mentioning. But start us off on that first set of research that you did, and that was the “Kinematics of the equine temporomandibular joint.” First of all, can you break that down into layman's terms as to what exactly is that on the horse and what does that mean? And then more into the objective of the study?


Dr. Stephanie Bonin, PhD, PE (12:17):

Yep. So, I think we can all relate to what a temporomandibular joint is. So, it's our mandible, our jaw articulates with our maxilla through this joint at the temporal aspects of our skull. And so, you know, sometimes people will say, "Oh, I have TMJ.", they'll use it as sort of a diagnosis. Like, well, everyone has a TMJ, but they mean that they have maybe some abnormalities with their joint. So, for horses, anatomically it's similar that it's the way that the mandible articulates with the skull. It's that particular joint and it's up fairly, almost behind the eye location below the ear. So, there, you know, the jaw is very long and so it articulates that would be caudally on the head, from an anatomical perspective. So, back away from the nose, and kinematics simply means movement. So, describing three-dimensional movement.


Dr. Stephanie Bonin, PhD, PE (13:09):

So, we want to know how something moves in space. So, the general term for describing movement is kinematics. So, that the title of it being the kinematics of the equine temporal mandibular joint is really just describing how that joint moves. Well first, we needed to make sure that we could proof of concept, more or less. So, using these techniques of applying retroreflective, so markers that reflect back to cameras, applying markers on the skull and applying them on the mandible when the horse chews with these markers on them, can that set of markers be used to describe what's happening at the joint? And so, this was a smaller study, it had four horses. I don't remember the details of how many trials I collected, but, so let's say there was like four chewing cycles in a trial and I might've collected like six trials per horse and followed how these targets moved in space while they were chewing. So, this first study only looked at chewing grain. So, I'm not comparing any differences in feed products here, but being able to establish the protocol of using these targets to describe the motion, that was, sort of, the basis or the goal of that particular paper.


Dr. Tania Cubitt (14:18):

And for our listeners at home. So, you were measuring the bite patterns of these horses, but there was a reason why you decided you wanted to do that. What was kind of the reasoning behind, I know that we measure gait when we're evaluating lameness. So, what was the reason behind wanting to look at how a horse chews?


Dr. Stephanie Bonin, PhD, PE (14:38):

Yeah, that's very important. Like why do you even want to know this , there were some prior studies that had attempted to quantify this movement and in some of those discussions there was descriptions of how this motion is different depending on what the horse is chewing. So, when they're chewing grass and particles that have longer lengths, that they tend to have more movement overall, compared to something that has a smaller particle size. Or another looked at fiber content, water content, you know, more fiber content, they had more range of motion, than less fiber. More moisture content had more range of motion. So, the limitation of some of those studies was the way that they tried to quantify this movement. So, one cleverly attached more of an analog way of doing it. So, attached a device over the skull and then another one on the mandible and then almost had like a pen and a paper that would describe the movement of the jaw.


Dr. Stephanie Bonin, PhD, PE (15:37):

The tablet would effectively be held stationary by the skull and then the mandible would have like the pen on it to trace the pattern, which is a, you know, not having sort of, this was in I think the forties so before motion capture was performed. Yeah. So, that was a good start. There was another author that tried to describe it but look more at the lips, you know, and these tissues are very mobile and what's happening at the lips is not necessarily what's happening at the teeth or at the jaw. So, this was a way to look at what's happening on the rigid parts of the skull and the mandible and to be able to describe those in three-dimensional motion to see. And then, now that we can describe the motion, the next step is I'm sure we'll get to the second paper and looking at the comparisons of feed products. And you know, as a master's scope it's fairly narrow and I could have looked at all sorts of feeds and varied fiber content more or moisture content more. But for the scope of the work that I was doing, it was basically the second one was looking at two different feed products to answer the question about the length of the particulate that they were eating, if that had any effect on how much movement that the jaw had during chewing.


Dr. Tania Cubitt (16:52):

It may have just been a master's project, but I referenced this work all the time when talking to horse owners because we have completely changed how they would normally, anatomically eat. What they would normally eat. And that changes chewing and changes dental wearing, so much information was gleaned. So, I appreciate that.


Dr. Stephanie Bonin, PhD, PE (17:14):

Yeah, I mean, and not only the dental aspect of it, of like now that we're changing how horses are chewing, they're not abrading the entire surface of their teeth anymore. We get these hooks that need to be abraded down. But then also, from a performance standpoint, when we want to have flexion at that atlanto-occipital joint, you know, the poll basically, you're going to have forward translation of the mandible relative to the skull. Now that there are more hooks that have formed because of the way the horse is chewing differently, that might be perceived as a behavioral issue because the horse is in pain now because we put a tight nose band on them, and then we had a drop nose band on them .


Dr. Tania Cubitt (17:50):

I'm hearing a whole other topic of conversation about the dressage world. It's controversial, we won't get into that today, but oh.


Katy Starr (17:57):

Yeah, that's interesting. One thing I wanted to ask you about, because you were mentioning those previous studies that, kind of, initially piqued your interest with doing this and how one of them had, you know, used the lips and things like that. So, how exactly did you decide where that you wanted to place those markers? Hopefully I understood correctly there were points where like the lips have a little bit more flexibility to them. And so, how did you decide where to place those markers to make sure that you weren't, you were actually getting the true movement of what is occurring and not by how you are manipulating some of what could have, you know what I mean?


Dr. Stephanie Bonin, PhD, PE (18:34):

Yes, no. That's a great question. In both human and in this particular study, whenever we're placing markers on the skin, we want to choose places where there is very little relative movement of the skin to the bony landmark underneath it. So, if you wanted to know what's happening at your knee, you need to know what's happening at your femur, your thigh, and your tibia. When you're picking landmarks, if you put markers all over your thigh and then you start walking, you've got all this soft tissue movement and so you get a lot of noise in the data and then you're not really tracking what's happening at the femur. So, you pick bony landmarks on either side of your knee and you pick one at your hip that are more tightly coupled to the segment. So, for the horse here, the skull was fairly easy. I mean there's a lot of locations on the skull where you can place markers and distribute them appropriately.


Dr. Stephanie Bonin, PhD, PE (19:25):

So, when you go back and try to use the data, you need to have enough variability in how they're placed so that you can capture all the movement. So, the skull is fairly straightforward. You can put it on the nasal bone and have good adherence of the skin relative to the bone. The mandible, the locations that I chose, actually there's an image in both papers that describe it but chose, sort of, the edge of the ramus. So, the large bone of the mandible along the edges from palpating and a little trial and error frankly, to be able to, you know, look at the data so, oh this is too noisy, let's find a better location. Finding locations where there's good adherence of the skin relative to the bone. So, placing them on there because you're relying on those then when the horse is chewing to quantify that movement. there's a couple other, like more nuanced things. Like right at the level of the TMJ, we want to know what's happening there.


Dr. Stephanie Bonin, PhD, PE (20:15):

So, I would place markers on the skull side and the mandible side of that joint, but when the horse is moving, those particular markers will move too much and you're missing a lot of that movement. So, there's some techniques where you can, you place them there, you look at where all of the markers are relative to each other, and then you take them off when you actually do the study. But you can go back and use that data because you know where those joint markers are relative to the rest of your, you know, the mandible or you know, where they're relative to the skull. So, techniques like that, which are pretty typical and gait analysis were used here.


Katy Starr (20:51):

Before we jump into your next study where you, you know, more differences between the type of feed that they were consuming. What ended up being more of the results of your research? What did you determine from doing this and was there anything that kind of surprised you and your team with it?


Dr. Stephanie Bonin, PhD, PE (21:09):

So, the first one, you know, as I mentioned it was more of being able to establish how the marker system is going to be used. Write the code to analyze the data, to be able to see can I identify from the data the different phases of a chewing cycle. So, the opening phase, the closing phase, and then the power phase, which is you know, the actual grinding particulate between the teeth. And so, you can actually see those when you break out the data in the different axis. So, you can "pitch, roll, and yaw", is a term that's used like in aeronautics. So, pitch is up and down. Roll is sort of like rolling along the long axis. And then, yaw would be, sort of, like if it were a plane, it would be, sort of, like swiveling left to right. And so, that same sort of descriptors were then used to describe how the mandible moves in terms of pitch, roll, and yaw. And so, those phases of the different portions of the chewing phase can be identified when you break out the mandible movement in those terms, pitch, roll, yaw. So, you know, at that point it was like, okay, well this is a robust way of doing this, it's time to now look at changing the feed product and seeing if there's a difference.


Katy Starr (22:17):

And were there any similarities that you noticed, I know you were working with, you said four horses, but were there any similarities or differences between the individual horses in terms of their temporal mandibular joint motion?


Dr. Stephanie Bonin, PhD, PE (22:29):

So, generally they were about within 10 or 15% of each other, in terms of their range of motion. So, you kind of have to consider, I don't recall the height of all the horses, but I didn't look at let's say, you know, ponies or miniature horses. These were all, you know, let's say 15 to 16 hand high horses. Some would only chew on the left and some would only chew on the right. I think it was broken out for that particular study about half. That's not to say that that's how they always chewed, was on the one side, but for the time that I was measuring them, they were only chewing on one side or the other. But overall, their motion was fairly similar.


Katy Starr (23:06):

That was another question that I was interested about was knowing how the horses actually, like when we think about how we eat, like, I mean there might be certain reasons why we might eat on one side rather than the other. But just wondering how horses tend to do that, if some of them more consistently, you know, chose one side or the over the other or if they were consistently using both sides. Because in my mind I'm also thinking, you know, and we'll probably get more into this later, but you know, the more frequently they're chewing on one side, I mean how's that going to impact once they need to have someone come out and do a dental exam? Like the wear on the teeth, depending on, you know, what they're consuming if one side is going to wear more than the other or how that worked?


Dr. Stephanie Bonin, PhD, PE (23:45):

So, yeah. I didn't observe them over a longer period of time other than like the duration of this and as curious as I am, like when I'm out riding, letting the horses graze afterwards, I haven't really looked to see like are they always chewing on the left or the right? But I don't know, to be honest, I'm not sure if they're always one sided or if they vary or maybe after they have a dental treatment they're going to change and you know, for some reason chew on the other side.


Katy Starr (24:10):

One of the questions I actually wanted to ask about, are there any specific signs or behaviors that horse owners maybe need to watch for that could indicate that their horse does have, kind of, a temporal mandibular joint motion issue, kind of, based off, you know, what you've done with your research so far?


Dr. Stephanie Bonin, PhD, PE (24:27):

Well, I would always defer to the vet, but you know, being a horse person and understanding somewhat about the, you know, the dentistry practice and goals, you know, if they're dropping food, if they're not able to, you know, fill up the lower part of their mouth with food before passing it to the back. I mean, of course if there's any, you know, bleeding or, you know, obvious signs like that. But I would say, you know, potentially from a riding perspective, if you're having issues where you feel like they're, you're not able to get them soft in the hand and supple and/or there, what seems to be, a behavioral issue as you're trying to, you know, maybe ride them in a more collected way. I think always going back, making sure there's nothing clinical or medical before, assuming it's some sort of behavior or training issue just to ensure that there's no clinical or medical reason that could explain it.


Dr. Tania Cubitt (25:19):

And what I use in my practice every day talking to people was, one of the things that came out of it, was the actual duration, the time that they were chewing. There are very few horses that I recommend have a completely pelleted diet. I mean, if you're old and you've got no teeth and you've got to drink your food because you got no teeth, then that's one thing. But I do have a lot of clients specifically in California that hay may be harder to store, harder to come by. So, they will lean on more of a pelleted forage diet to get their fiber requirements. And then, if you go further down the digestive tract, okay, if we take away what else happens when they're chewing, they're masticating, they're mixing with saliva. So, if we shorten that, then we shorten the amount of saliva that is produced and now we go to the stomach and it's not like the mouth isn't just separate from the whole body. Everything is a chain of events, that's where it starts. And so, then if we're just on pelleted and we're not producing saliva and then we're not getting that saliva buffering that stomach acid, what's one of the biggest problems in horses today? Is gastric ulcers. So, that was something else huge that I took out of this was just the time that it takes to chew long stem fiber. So, what else was happening was the production of saliva.


Dr. Stephanie Bonin, PhD, PE (26:39):

That's a great point and that was one of the metrics that I looked at looking at the pellets versus hay, not only just the overall motion but their frequency. So, how quickly were they chewing and the time that it took them to complete a chewing cycle. So, for hay, they chewed slower, and they took longer time, like the frequency was lower and the therefore the time that they spent chewing was longer than for pellets.


Dr. Tania Cubitt (27:03):

And when we stick horses in stalls, one of the things that we constantly see, it's an uphill battle trying to mimic grazing behavior, right? I can't give horses all the grazing in the world, that's just not available. So, when we put them in a stall and we're still trying to mimic grazing behavior and people are feeding pellets and you know, they're chewing so quickly, it becomes very challenging to manage that horse. So, this is a good way for me to show people there's actually research done looking at the time it takes to chew that kind of thing. And so, showing people pictures like this is much easier for me to kind of implement management strategies with folks. So.


Katy Starr (27:47):

Yeah. And this study, this one was the “Comparison of the mandibular motion in horses chewing hay and pellets.” Did you happen to use the same horses or how was your setup for this one and did you make anything different from what you determined from your last one?


Dr. Stephanie Bonin, PhD, PE (28:05):

Yeah, there were more horses. There might have been duplicates because you know, I'm relying on my barn friends, "Hey will you trailer in and stand around for four hours while I do this in the winter ?". So, there were some repeats for that study, but there were more, and this maybe double the numbers and the setup was the same in terms of the marker locations and the protocol was the same, you know providing either the pellets or the hay. I let them chew for at least two minutes to make sure that any prior food was cleared out and they're only chewing what we're looking at or what we want to evaluate. And then getting good trials. And when I say good trials, I mean all of those cameras that we looked at before that are surrounding the horse, feeding them, but I can't be in the way so I have to make sure that I'm, you know, ducking down and, and ensuring that all of the markers can be seen by the cameras because at least two cameras you have to see these markers at all times in order to properly track them. So, you collect enough where you can go back and find good data, meaning you've tracked all of the markers that you need in order to run the analysis. So, did that for hay and then for pellets all of the horses and pulled out some of the same metrics that I did the first time. In terms of describing the motion, the pitch, roll and yaw. But also, as we just discussed, some of the frequency, how quickly they were chewing, how long it took them to chew the different pellets versus hay.


Katy Starr (29:30):

And you mentioned this a little bit before when you were talking about those previous studies from a little bit before all of our time where you were looking at, you know, the fiber content and the particle size and moisture content. You focused on this one specifically on the fiber content and particle size, rather than the moisture content, since they're similar right? Rather than pasture grasses and things like that.


Dr. Stephanie Bonin, PhD, PE (29:54):

That's right, yes. So, the moisture content was similar between the pellets and the hay. I believe the hay had slightly more fiber than the pellets. So, it's not a true control, in so far as it being the only difference is particle size. So, we do have a difference in fiber and particle size, but the primary motivation was really particle size, I guess. I don't know enough about fiber content, like can you come up with a pellet that has the same fiber content as hay? Is that even reasonable to do that?


Dr. Tania Cubitt (30:25):

I think it comes then to just the fiber length, is what really was changing. Yeah.


Dr. Stephanie Bonin, PhD, PE (30:31):

You know, absolutely. Yeah.


Dr. Tania Cubitt (30:32):

Fiber content. Yeah, I mean.


Dr. Stephanie Bonin, PhD, PE (30:33):

Yeah, so I don't know if it's even possible to come up.


Dr. Tania Cubitt (30:36):

A hay pellet.


Dr. Stephanie Bonin, PhD, PE (30:37):

I guess I don't know if you can find pellets that have identical or you know, similar fiber content. So, for this study the goal was to look at the length, you know, the pellet size.


Katy Starr (30:47):

How far it was already broken down when the horse is chewing, how much more work they needed to do rather than it partially being done for them. So, I know that you weren't comparing the grain, you know, because that was what you used in the first one and the second one you did the hay, the long stem hay and the pellets. So, did you try to make some observations based on that first study with the grain to the pellets and the hay in general, even though that wasn't specifically what you were looking at?


Dr. Stephanie Bonin, PhD, PE (31:18):

Yeah so, in hindsight I probably, as part of my discussion for the second paper, could have also included the data from the grain, in terms of statistically looking at, in research you can't really say something is the same or different unless you do some stats, you run some statistics and you say it's significantly different. Otherwise, you can say they're not different. I.e., you know, they're the same. Just looking at the data, the overall trends, the grain did not look to be any different, significantly different from the pellets. So, you know, again, the particle size of grain is on a similar scale as it is the pellets. So, the data for those two studies, although I didn't run the stats on them, they look very similar.


Katy Starr (31:58):

So, if you were to do either of these studies again, you kind of mentioned a little bit with your discussion on that second one, but is there anything that you think you would do differently? You know, hindsight after, you know, going through it. You're like "Ah", you know, if I could have done this over again. Knowing this now, I would've done this.


Dr. Stephanie Bonin, PhD, PE (32:18):

Yeah, I might have included some of the cubed hay that I see so much of now.


Dr. Tania Cubitt (32:24):

Because I just kind of extrapolate and say, well the fiber lengths in the middle, so I'd put it in the middle.


Dr. Stephanie Bonin, PhD, PE (32:29):

That's right. Yeah. That would be the starting point to see. But that's a common product that I see, you know, at the stables and people are feeding these cubes of hay instead of, you know, the flakes of hay. So.


Dr. Tania Cubitt (32:41):

Mm-Hmm , Texas and California. Very common. I can't remember in your study, because I took your data and then coupled it with some other research. Where was the horse's head position? Were they eating, were you holding the food close to the ground, or normal kind of chest height or?


Dr. Stephanie Bonin, PhD, PE (32:57):

So, I was squatting.


Dr. Tania Cubitt (32:59):

Kind of holding it where a bucket would hang?


Dr. Stephanie Bonin, PhD, PE (33:01):

Probably a little lower.


Dr. Tania Cubitt (33:02):

Okay. Mm-Hmm .


Dr. Stephanie Bonin, PhD, PE (33:03):

It could be about where a bucket is. So, I was, you know, effectively kneeling and then holding the food in front of me. So, their neck was relatively horizontal. Maybe the poll was a little bit lower than the withers. Yeah. They weren't in like the grazing posture. They weren't. So, it's probably.


Dr. Tania Cubitt (33:20):

That's what I have on the one slide that I use all the time, is your data coupled with some work done in 2021, looking at the height of where they're eating from, whether it be chest height or off the ground, and the amount of jaw sweeps that will occur based on that position as well. So, take away what they're eating. Well, they actually did it with hay and grain, but the actual height that their head was and the closer to the ground, again, was even more jaw sweeps versus at chest height.


Dr. Stephanie Bonin, PhD, PE (33:50):

Oh, interesting. Yeah.


Dr. Tania Cubitt (33:51):

So that was interesting.


Dr. Stephanie Bonin, PhD, PE (33:52):

More support to let your horse live naturally, live as it's designed to live.


Dr. Tania Cubitt (33:57):

live and feed off the ground. Exactly. Not only did it do that, but it kind of more appropriate teeth alignment, when they had their head closer to the ground. One thing that we see a lot, anecdotally, with a lot of the slow feed hay nets and, you know, there's actually been quite a lot of work at Michigan as well with this, but when they first came out, pony club, everything, 4-H. Hang your hay net up high and so then, you have this tiny hay net hole, and are these horses are getting so angry and they're yanking. And anecdotally, people are saying my horse has got like neck pain because they're doing all this yanking. So, you know, now closer to the ground, a more of a, more normal like grazing, chewing, pulling versus yanking to the side.


Dr. Stephanie Bonin, PhD, PE (34:46):

Why was that advice given, to hang your hay nets high? We all did it, but I don't remember why.


Dr. Tania Cubitt (34:52):

So that when we put shoes on horses that they wouldn't paw the food and put their, you know, every problem in horses today is due to something we have done with them. So, just say people .


Dr. Stephanie Bonin, PhD, PE (35:05):

I think it's in maybe some of the background information for the second paper when you look at..


Dr. Tania Cubitt (35:09):

The war? I use that reference all the time.


Dr. Stephanie Bonin, PhD, PE (35:11):

Yeah, well you look at fossils…


Dr. Tania Cubitt (35:13):

You look at the Cavalry horses.


Dr. Stephanie Bonin, PhD, PE (35:14):

Yes. You look at old horses, like they have no dental issues, and you start to look in modern day and we've got all these problems. So, it's um.


Katy Starr (35:20):

Like how did this happen? Oh, oh , whoops. I guess that was us . So, obviously, you know, the current research and where you're at in life right now is leading you more towards, you know, the path of like the equestrian helmet impact and some other things in that way. But if somebody was, and Dr. Cubitt, you mentioned a little bit of that research about the level of the head when they're eating and everything. But if you could kind of like jump on beyond what you've done with these studies and you were to continue doing research in this area and both Dr. Bonin and Dr. Cubitt, you could, you know, talk about this a little bit, but I'd be curious to know like what would be next steps for us? Like what would be interesting for us to explore and questions that we'd like to see answered in this area?


Dr. Stephanie Bonin, PhD, PE (36:10):

There has been some work done looking at the effect of bit position and bit placement within the mouth and what parts of the bit engage with what parts, the very structures in the mouth. But I could see there could be a direction of looking at the effect of the malocclusions or some of the hooks and the various issues that we bring equine dentists in to fix, what the effect is if, you know, you could design a study to look at that or to be able to quantify for example, if, you know, when we do ask for flexion, how much relative motion you get of the mandible to the skull, how that changes. So, to quantify those problems, those, you know, hooks and whatnot beforehand, try to measure that, get your dentist there, , remove all of those, and then measure that again to see, you know, how forward and backward translation of the mandible changes with the dental procedure. That could be another similar type of, you know, looking at kinematics, looking at movement, but more of the treatment aspect of it, you know.


Dr. Tania Cubitt (37:17):

Yeah, and I think the research, if you look at the research that's going on, especially at Michigan still and Minnesota, that group, it's really in the world we're in today about animal welfare, understanding what is normal and natural for the horse and then how in the situations we put them in, how do we mimic that or how do we make the two worlds come close together, you know? It's just constantly moving in that direction. So, understanding how they're chewing, understanding based on what we're feeding them, how they're chewing, how that one direction you can go, is bit position. That's, you know, kind of riding animal welfare but also, you know, when we're looking at the hay nets or the things, the tools that we're using to actually feed these horses, the management, I think that definitely understanding what is natural and normal, constantly being able to work towards that in the settings that we put horses. Because we're never going to have them live out on the prairie and eat a wide variety of forages, but...


Katy Starr (38:23):

As close as we can get to that. Yeah, yeah. And then again, I think this is a very good and valid question for both of you, but how can horse owners apply, I mean, Dr. Cubitt, you've talked a little bit about how you've used some of her research and the talks that you've given and how horses are, you know, they're naturally designed movements and everything. But how can horse owners take and apply what you've learned from these studies to help improve how they care for their horses?


Dr. Tania Cubitt (38:54):

For me, it's number two of every presentation that I give. I can't talk about the rest of the digestive system until you've talked about the mouth. That is how food gets into the digestive system. If it can't get in, forget about the rest of it. So, the mouth is really, we typically jump to the stomach as the first part of the digestive system. The mouth is the first part of the digestive system and it needs to function correctly. You know me with everything we talk about is, well, what is correct, what is normal? You can't fix something if you don't know what is normal. So, understanding that these studies were some really eye-opening early research looking at in more of a scientific manner than just the horse's drawing its own picture of how its mouth is working, really getting a deeper understanding of how the horse was eating. From there, I know a lot of European work has looked at fiber length, from fiber length then you can go further down the digestive tract and look at gut health and that kind of thing. But anyway, this is the second slide in every presentation I give, whether it to be 4-H kids or veterinarians, is how the mouth works.


Dr. Stephanie Bonin, PhD, PE (40:05):

Yeah. And I think knowledge is, well the old adage "knowledge is power".


Dr. Tania Cubitt (40:10):

Knowledge is power.


Dr. Stephanie Bonin, PhD, PE (40:11):

But truly, it is. If horse owners understand these principles and the benefits, that if the particular place that they're boarding at uses hay nets or uses only pelleted hay or something like that, the information is available for the management of that property to change, to do something that's more beneficial for the welfare of the horse. And I think horse owners are, particularly riders, they're particularly savvy with getting information and making use of it. I mean, I can just speak from like the helmet world and people want to know details and they want to know why, and they want to make decisions that are best for their horse and best for themselves. So, I think having that information, they can then, with data, ask for things. If things can be moderated, you know, adjusted in the way that they're particular stable is managing and feeding and whatnot. They can have a basis for their request.


Katy Starr (41:10):

And in the research that you did in terms of wear on teeth, I know you said it wasn't for a really long duration, but was the comparison of like a long stem hay versus like a pelleted hay or grain, was there anything that indicated how management, and again, right, working with our veterinarian and everything, but just in terms of what you observed, is there anything that kind of influenced how frequently a horse might need dental examinations? If they're consistently eating one or the other or anything like that between your, your research?


Dr. Stephanie Bonin, PhD, PE (41:48):

That wasn't one of the questions that I was looking to answer, but I guess maybe we could just talk about the actual results from the pellets versus the hay in terms of when chewing pellets. The amount of lateral excursion, so how much they move their jaw sideways, was about 75%, three quarters the amount of length or lateral movement that they used when chewing hay. So, their range of motion is reduced by about 75% laterally. And so, you know, in terms of, well, what's happening at the level of the teeth, the narrower mandible, the teeth are straighter along the mandible itself versus the maxilla. The skull portion, the teeth are set further apart slightly, and there's curvature to them. So, you've got sort of a mismatch in geometry when the mouth is closed. But in order to abrade the entire surface of the tooth, the mandible has to move far enough laterally, to the side, in order for the entire surface to get worn. When chewing the pellets, the movement is more up and down and less lateral. So, the movement doesn't allow for the entire surface of the tooth to get worn down. And that's where the, you know, the power tools have to come out and make those surfaces level then because the continuous growth of the tooth allows for those, you know, edges to form. So, it comes down to eating grain and pelleted foods, probably will need more frequent dental treatments than if they're out forging or eating primarily hay.


Katy Starr (43:22):

No, that's excellent. That's, kind of, I wanted to make sure that when we rounded out this episode a little bit, that our listeners kind of had that understanding of, you know, this is how they eat and this is how they eat different types of feed, and this is basically what can happen, you know results from that. Right? And so, that kind of just, I think it just helps set people up a little bit better for awareness and understanding what's happening to their horse in a little bit of a deeper level. Because sometimes, I don't know that that's always observed. And like you talked about initially, when we're discussing there's possible behavioral issues that could come from this, and people may not always make that connection. And that could be like beginning horse owners, but that could be people that have had horses for a while, but maybe they're just not as in tune with some of this.


Katy Starr (44:08):

And so, hearing this, it's like, "Oh, I wonder if this is something that could be a problem for my horse?". And so, Dr. Cubitt, like when you say that you're trying to find solutions to issues that come up, you usually go through this checklist that you go down the line of, "Okay, well we know we can just, you know, scratch that one off. We know it's not that.". And so, sometimes it's a matter of doing things like that to be able to determine, you know, what the actual issue is for that horse. And so.


Dr. Tania Cubitt (44:34):

And oftentimes, I mean, nine times, I would say 9.9999 times out of 10 people come to me and say, "Oh, my horse is crazy. I need a calming supplement.", but more often than not, the horse has changed its behavior as a pain response. And we typically go to, "Oh, is he lame? Is there something wrong with his foot? Has he got a muscle issue?". But the head and the connections, the jaw connection, those muscles, how they're eating, what's happening in his mouth often doesn't get thought about as much. When we have that conversation about pain, and maybe this presentation, and skimming through these articles will certainly, "Oh, maybe I should be thinking more about, you know, I haven't found anything wrong with the rest of my horse's body. Maybe I should be looking to that area to look at pain, to look at what could be going wrong in there.". You know, most people dental care is like deworming. I deworm my horses every six weeks and I change the dewormer. I do dental work on my horse once a year, but you know, every horse is different and maybe some horses you have to do it more frequently or maybe we should be looking there first when your horse is shaking its head.


Katy Starr (45:48):

Yeah, yeah, exactly. Well, Dr. Bonin, how can our listeners stay connected with you or dive a little bit deeper into your research?


Dr. Stephanie Bonin, PhD, PE (45:56):

Well, I do have a LinkedIn profile. I'm not super active with my social media aspects, but it's there and I can be connected through that media. ResearchGate is another source that has perhaps all of my literature that I've, you know, not just these temporal mandibular joint studies, but some of the other things too. But I think I've made them all available for free. You don't need accounts or whatnot, you can just download the articles right from there if you wanted to sort of dig into it or look at some of the figures that show the comparison between the feed products, you know, where these markers were placed. If any of those questions come up, they can look directly at that source material.


Katy Starr (46:36):

And we'll be sure to link those in our show notes. So, if anybody would like to get to those easily, we'll put those in there for you. And to our listeners, if you have any other topic ideas that you would like us to discuss on the Beyond the Barn podcast, please reach out to us at We love to hear from you. And Dr. Cubitt and Dr. Bonin, thank you so much for being here with us today. I think this was a very interesting conversation for us to have about how our horses eat.


Dr. Stephanie Bonin, PhD, PE (47:04):

Thank you for having me.


Dr. Tania Cubitt (47:06):

Excellent, thank you.


Katy Starr (47:09):

Thanks for listening to the Beyond the Barn podcast by Standlee Forage. We'd love for you to share our podcast with your favorite people, and subscribe on Apple, Spotify, or your favorite listening platform. Until next time, keep your cinch tight and don't forget to turn off the water.


If you enjoy the Beyond the Barn Podcast, please consider taking a minute to rate and review the podcast on these popular platforms.