Ep. 095: Metabolic Horses Aren’t Always Fat - Here’s What No One Tells You - Part 1

Episode Notes

On this Part 1 episode, co-hosts Dr. Tania Cubitt and Katy Starr have a conversation with Dr. Erica Macon, assistant professor of equine science at Texas A&M University, to talk about the challenges of managing equine metabolic disorders, including:

• Why horses that appear lean can still be at risk for metabolic issues
• The differences between insulin resistance and insulin dysregulation
• Common misconceptions about “low NSC” feeds
• How subtle signs like a cresty neck can indicate underlying problems 

And be sure to tune in to Part 2, which will release June 17th, where Dr. Macon shares the results of how Standlee pelleted forage impacts insulin levels in metabolic horses, potential feed management ideas that could help metabolic horses, and we discuss how and why horses might get laminitis in the winter.

🎧 Listen now on the Beyond the Barn podcast!

Have a topic idea or feedback to share? We want to connect with you! Email podcast@standlee.com

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

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Nutritional resources from past episodes – 

• Ep. 088: NSC, Sugars, Starches, Fructans – Are They Good or Bad for Horses?
• Ep. 084: How to Help Your Horse with Cushing’s Disease
• Ep. 057: How to Prevent and Manage Laminitis
• Ep. 006: Successful Strategies to Help Limit NSC (aka Sugars and Starches) in Horse Diets
• Ep. 005: Are Horses Carbohydrate Sensitive?

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Read full episode transcript

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 back here with us today.

 

Dr. Tania Cubitt (00:35):

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

 

Katy Starr (00:38):

Right. We have an excellent guest joining us on today's podcast episode. Our next guest is an assistant professor of Equine Science at Texas A&M University. She specializes in equine nutrition and endocrinology with a focus on insulin dysregulation and metabolic disorders in horses. Her research is helping shape how we understand and manage conditions like equine metabolic syndrome and laminitis. She brings a practical perspective for horse owners grounded in science but driven by real world application. We'd like to welcome Dr. Erica Macon to the Beyond the Barn podcast. Thanks for joining us Dr. Macon.

 

Dr. Erica Macon (01:19):

Thank you for the invitation. I was really excited when I got your email. I was like, oh yeah, I'd love to join.

 

Katy Starr (01:24):

Yeah, no, we were so excited. Dr. Cubitt was talking to me a little bit about some of the experiences she had and some of the talks you've been doing at AP and some things like that. And the topic I think is excellent and very relevant to our podcast and what our horse owners that listen to the podcast really would be interested in learning more about. And so I think it'll be a great conversation today.

 

Dr. Erica Macon (01:46):

Yeah, I'm excited.

 

Katy Starr (01:47):

And just for our listeners, as a reminder, 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. 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 to talk directly with Dr. Cubitt or Dr. Duren or Dr. Macon if you would like to reach out to her as well on any specifics that you would like to know. So, Dr. Macon, why don't we just get started. Tell us a little bit about your background with horses and where you grew up.

 

Dr. Erica Macon (02:21):

Yes, of course. So, I'm originally from a little town called Fort Pierce, Florida. My family, actually, they're a fishing family because we grew up on the coast. My grandfather started a wholesale fishing company and then his daughters, one of them being my mom took it over. And so I spent a lot of my childhood growing up, cast netting and catching fish. But my real love and passion was being at the barn with horses. I never got the opportunity to show or do anything like that because my parents were very adamant on, "you'll never make a career out of horses." And I proved them wrong.

 

Katy Starr (02:59):

.

 

Dr. Erica Macon (03:00):

So, horses were more as a tool, not so much for pleasure, but as I've aged and had more horses, you know, now they're my sanity and my happy place when I want to escape from the world. So, growing up I had quite a few different horses and my first real passion for them was in veterinary medicine. And I thought like most young people, you want to be a veterinarian. And then you go to undergrad and you see all the different opportunities available to you and you're like, wow, I know I don't want to be a veterinarian. I want to go this route. Or you want to go a different route. And there's so many different options once you're exposed to them. And that's kind of how I ended up into research and everything.

 

Katy Starr (03:40):

That's awesome. Well, and one thing that you kind of talked to us a little bit earlier was how some of this stuff, it didn't always necessarily come easy to you. And we talk about how in some of these career paths, right, it could be as a veterinarian or as a PhD researcher, any of those kind of things. I think there's kind of almost this expected of what you would see as someone who is just this like brilliant, everything comes so easy to them. It just seems like it's such a natural fit, but sometimes it's not always about getting all of the A pluses and the 4.0's and all of that stuff. So, talk to us a little bit about your experiences with that. Because I thought that was really interesting and fascinating and something that could be very encouraging for lots of those that have the desire to follow that career path. But they're like, I could never do that.

 

Dr. Erica Macon (04:32):

Yeah. And that's where I think growing up you kind of lack that confidence. And that only comes with time, and the more time you spend doing something and you're like, oh hey, it's like after you get a PhD you're like, I'm not that smart as some of like my senior colleagues. And you surprise yourself with how much you know in a different situation. But yeah, growing up I had a lot of learning disabilities. I was taken out of like a normal sized class and I was put in very small, like two to three kid groups because I couldn't keep up with all of my other classmates. And I was tutored in this tiny classroom, same tiny classroom until I was in the sixth grade. And that continued. But I just had a lot of different mentors that really helped me get over some of those learning disabilities.

 

Dr. Erica Macon (05:22):

And even today I'm still like working on how I learned best and things like that. But I really did struggle. You know, I had a 3.1 GPA as an undergrad, so that's not something that you go home and you're like showing a piece of paper to your parents. And I said that I'm pretty sure when I was interviewing for my master's position, I said, I may not have the perfect grades but man, I'm going to work harder than anybody else. And I would like to think I've done that every place that I've gone. And I grew up in 4-H raising livestock, beef cattle, as well as pigs. And I take the 4-H motto very seriously. You make the best better. So, I like to leave a place better than what I found it and if I can help individuals along the way. So, happy to do that. And that's one of the reasons why I like to mentor so much. So, I really did struggle, but I always tell people, and I give this same piece of advice to the undergraduates at A&M and any other institution I've been at. I'm not smart, I'm just motivated. Like I just want to find the answers, why don't we know this information and then do the hard work that it takes to try to figure it out. So, yeah, that's my little shtick.

 

Dr. Tania Cubitt (06:38):

and Dr. Macon won't toot her own horn, but as the young kids say topics trend. And right now Dr. Macon and her research is definitely trending. You are at the forefront of a lot of this insulin and glucose research, metabolic disorders. You're being invited to speak at the world's leading stages as an expert on this topic. So, you have proven that not only did you work hard, but yeah, you made it, you're there and you're making a huge difference. 

 

Dr. Erica Macon (07:11):

I appreciate the compliment. I probably, most days wouldn't agree, but I still keep telling students these days that I'm just getting started and I'm in the beginning of my career. I have way more to go.

 

Katy Starr (07:23):

But that's exciting too, just to see how much that you have accomplished and where you've gotten. But knowing that there's so much more ahead of you, I just feel like that's something so much to look forward to and just to so many problems to solve. Right. Which I think is exactly kind of what your career path entails and everything, which is very exciting.

 

Dr. Tania Cubitt (07:43):

What's the acronym PhD means piled higher and deeper. It means is all the things that you don't know .

 

Dr. Erica Macon (07:49):

Exactly. And that's exactly what I have people that interview for PhDs join the lab and stuff. And I said, what do you think a PhD gives you? And I've never gotten the answer that I, I want to hear. I hear, you know, it gives you respect and I have other opinions on that and it'll make you smarter. And I'm like, no, it gives you the ability to do anything. It trains your brain to think a certain way, to see something objectively, design an experiment to then go in and answer the question.

 

Dr. Tania Cubitt (08:21):

In my mind I was thinking it gives you the ability to ask more questions. It's always the next question you solve one and it creates another question. And that's why it's continually learning. The day you stop learning is the day you die.

 

Dr. Erica Macon (08:33):

Yeah, I 100% agree with that.

 

Katy Starr (08:36):

Yeah, that's awesome. Well and one other thing that you had mentioned is you have some horses now, right? Moose and Goose, is that correct? Tell us about Moose and Goose just a little bit.

 

Dr. Erica Macon (08:46):

Yeah, they're my off the track thoroughbreds. Moose is a 17.3 just big dyna former baby. Someone had originally repurposed some of the track to be an inventor, but he didn't like to fly. So, he is more of a flat source now. And I was trying to do some dressage with him, but he's been having lots of different suspensory issues and stuff. So, then I got my Moose a Goose and I found another off the track thoroughbred down here in Texas. And I'm currently working with him to maybe try to make him more into a dressage guy. Because I'm more fragile these days than I remember . And I don't know if, I don't know if jumping is a good idea for me anymore. Takes me out for too long.

 

Katy Starr (09:29):

. Oh yeah, that's excellent. Oh, I love that though.

 

Dr. Erica Macon (09:32):

But they're good boys. They're still my happy place. If I need to dissociate from the world, I go to the barn. And even if I'm just grooming and stripping a stall, that just helps me mentally. But yeah, I'm fortunate that I can have both those boys.

 

Katy Starr (09:49):

That's awesome. They're so good for like a mental reset.

 

Dr. Erica Macon (09:53):

Yep, they are. They remind me constantly why I decided to get into the field.

 

Katy Starr (09:58):

That's excellent. Well, and where did your interest specifically in the endocrine disorders come from?

 

Dr. Erica Macon (10:04):

Yeah, so I, when I think about that, I'm like, where did it come from? But I remember being an undergrad and I just, I was taking classes. I was an animal biology major in animal science because I was pre-vet track because you know, that's all I knew. And I just started, I loved principles of nutrition and then I loved that so much. I'm like, there's other nutrition classes. What? So, I went and I took equine nutrition, food animal nutrition. I did companion animal nutrition. I even took horticulture classes so I could understand how grass grows. And I fell in love with nutrition. That was the first one. And then when I was talking about going to grad school, they're like, you need to pick a species. And I'm like, why do I need to pick a species? Why can't I do all the species? And so I was actually between a pig and a horse because I heard my parents in the background saying, job security, we love bacon, you know, all the things.

 

Dr. Erica Macon (10:58):

And I was like, yeah, that's true. But I just love the GI tract of a horse. You know, you have a monogastric up front and you've got like a tiny little ruminant in the back. And when I was in undergrad, this might age me a smidge, that was in 2013, something like that. And I realized that the nutrition research that we had in horses, I mean really we didn't start equine nutrition until much later because we were just taking and repurposing ruminant nutrition and applying it into horses. But then you had some of like the biggest giants like Hintz and Potter and all those people that came along and started doing specific equine nutrition. And I thought to myself, there's still so much we don't know. So, in my mind that was job security. But I, of course I wasn't looking at big picture and I fell in love with the GI tract and I wanted to do equine nutrition research.

 

Dr. Erica Macon (11:54):

And so, I jumped on a project in my undergrad and I was looking at ammonia emissions from horses fed different crude protein diets. And I just remember it, I was doing a total urine and manure collection trial where you collect all the urine and all the manure out of these horses looking at the crude protein and the ammonia emissions. And I was just going down a barn aisle with a trash bag full of manure from each horse that I would need to mix together to get a very small sample. And that solidified my love for research. Why? I don't know, because most people would not be a big fan of that. But as Dr. Lori Warren at Florida says, I drank the Kool-Aid and the rest is kind of history. But then I jumped into endocrine research when I was in my master's degree, and I did my master's at Middle Tennessee State. And I was under Dr. Rhonda Hoffman, which I consider her the queen of carbs in horses. And a fantastic mentor. She mentors me to this day. And I'll throw another little piece of advice. You can always have a mentor no matter how old you are, I'll always look to my mentors and I, I text her quite frequently and I'm like, hey, don't think that I'm stupid, but I need you to remind me if this is right or not.

 

Dr. Tania Cubitt (13:09):

Validate this for me.

 

Dr. Erica Macon (13:10):

. Yeah. She's my little dictionary that I pull out.

 

Dr. Tania Cubitt (13:13):

You definitely always need that person that you can bounce the craziest idea off and they're never going to judge you. Yeah, I have one, it's Kristine Urschel, Dr. Kristine Urschel , University of Kentucky. Just to connect us even further. Yeah, when I was in graduate school, Dr. Hoffman was there for my master's as well, at Virginia Tech.

 

Dr. Erica Macon (13:35):

Oh yeah. And Dr. Urschel sat on my PhD committee. It's a very small world.

 

Dr. Tania Cubitt (13:41):

Yes it is. And I was in her wedding, so there you go. and saved her bridesmaids dresses. It's a whole story.

 

Dr. Erica Macon (13:48):

, it's a small world. We're all connected in some way. But yeah. And Dr. Hoffman, she actually paired me up with a different researcher at Emory & Henry University, Dr. Patty Graham Thiers and she was working on looking at plasma and muscle amino acids and insulin resistant at the time. And we can get it into terminology in a minute. Insulin resistant horses and compared to healthy horses, unfortunately I didn't find any differences, but that's okay. That's why you do research. And Caroline Loos did a lot more stuff after that and she's found out a lot about that. So, that was my first, hey, the endocrine system is really, really cool. You mess with one hormone, you mess with all of them in some way or shape or form. And then that's what took me to University of Kentucky because not very many people were specifically wanting to do endocrine stuff. Dr. Amanda Adams, who's an equine immunologist and she's also partnered with Mars Horse Care and Dr. Patricia Harris. And they were wanting to do nutritional work in metabolic courses. And I'm like, hey, that's exactly what I want to do. And it took me there. And really the rest is kind of history because that's all I've been doing

 

Katy Starr (14:57):

Ever since .

 

Dr. Erica Macon (14:58):

Yeah, ever since .

 

Dr. Tania Cubitt (15:00):

And I refer to Dr. Harris as Auntie Pat because that's how all my graduate work was funded through the Mars Horse Care as well.

 

Dr. Erica Macon (15:08):

Yeah. Dr. Harris was my go-to and she still is. I see her, I still have a hard time calling her Pat. I look at her, I'm like, Hey doctor. It's just like, stop doing that . And I was like, it's so hard. I've been working with you for so long. But yeah, I wouldn't be the scientist and thinker that I am without her guidance. So, I really appreciated that.

 

Katy Starr (15:30):

That's awesome. I love that. Well, let's get into our topic today. So, what are the most common endocrine diseases in horses?

 

Dr. Erica Macon (15:41):

Yeah, so the two most common are pituitary pars intermediate dysfunction, or what was formerly known as Cushing's diseases in horses and equine metabolic syndrome, insulin dysregulation. There's a lot of terms for these endocrine diseases. And they have been rapidly changing ever since roughly around, I mean, metabolic syndrome wasn't characterized until 2002. And then we didn't have a veterinary consensus on it until 2010. So, that tells you how, while 2010 was a long time ago, it really wasn't. When we think about research like this is a very, it's a new field and it's still rapidly evolving with all the researchers that are in the field and the equine endocrinology group. So, it's an acting group of veterinarians, mostly internists that specialize in endocrine disease. And they go across the world. There's some here in the US and Europe, Australia, it's a really, really great team of endocrinologists. And then this most recent, in 2024, they actually started including hypothyroidism and hypothyroidism in the EEG, which I don't think we'll touch on today. But I think you'll see start seeing a little bit more of that in the near future. But the two most common are PPID or Cushing's disease and insulin dysregulation or equine metabolic syndrome.

 

Katy Starr (17:02):

Okay. And can you just break down kind of a brief PPID or Cushing's, what happens to the horse with that? And then also for the insulin dysregulation also, just so we can kind of set the stage with those two as we talk through today. 

 

Dr. Erica Macon (17:18):

Yeah. So, PPID, this occurs because of an adenoma that forms within the pituitary, which is a low gland that hangs down in the brain. And the reason why we reclassified it as PPID instead of Cushing's is because when earlier researchers and clinicians were seeing the symptoms that these horses were displaying, it was very similar to the Cushing's disease that we see in dogs and humans. But until we started actually analyzing or looking at the brains of horses that had Cushing's, they had passed away. And then we started, I can't remember what researchers started doing that, but we realized that their adenoma, which is just a benign tumor, is actually found in the pars intermedia, which sits between the front half and the back half of the pituitary. Whereas in Cushing's disease and dogs and humans, it sits in the back half. So, it's more, it's just a, it's basically a more accurate description of what the disease is in horses.

 

Dr. Erica Macon (18:24):

And this adenoma that forms it basically takes over these dopamine neurons. And neurons are part of the nervous system, which actually help transmit different signals in the body and especially in the brain. And that's why you have, if you ever have like nerve pain or something like that, everything comes from the brain and the spinal cord and extends out into the periphery. But if we talk about the neurons within the pituitary and the hypothalamus, which is actually in the brain, you think about the relaying of a signal basically outside, say a horse, just for an example, a horse will, if you shake a scoop of feed, I bet a horse will pop up and their nervous system allows them to respond and to hear that and get excited. Or like Pavlov’s dog, you know, they'll start salivating if you start trying to feed them. So, you have the neurons within the pituitary hypothalamus, these dopaminergic or these dopamine neurons, they become overtaken by this adenoma or this benign tumor.

 

Dr. Erica Macon (19:28):

And when that happens, it basically takes that signaling away. And when they don't have that signaling anymore, everything that falls below that signal starts to go awry. So, what happens with that is they can no longer control, I'm going to just say as ACTH, it's another hormone because it's a very long word. And that particular hormone starts getting secreted at very, very high rates. And then if my saying at least is if you mess with one hormone, you mess with them all. Especially if you're doing something that's up in the brain and it just cascades down into the rest of the body. So, that's where PPID originates is from this benign tumor that takes over that signaling.  Now equine metabolic syndrome, that is really more of a characterization. So, it is a collection of symptoms or risk factors that predispose horses to what we call hyperinsulinemia-associated laminitis, which is a very long term for laminitis caused by high insulin levels in the blood.

 

Dr. Erica Macon (20:35):

One of those symptoms or risk factors is insulin dysregulation. And that's a collective term for both resting insulin concentrations as well as insulin concentrations after a meal, as well as tissue insulin resistance. So, the body can no longer act accordingly, or the body's tissues can no longer act accordingly to a normal amount of insulin. So, the body secretes more of it to say, hey, hey, we need to get glucose shuttled over here, but you're not responding to me, so I'm going to make more insulin and try to make that happen. So, that's why the terminology in equine metabolic syndrome, insulin dysregulation, they're very related, but not all the way, if that makes any sense.

 

Dr. Tania Cubitt (21:21):

When Katyand I were talking about this yesterday and why I thought it was such a good idea to kind of extrapolate on this, I think most of our listeners are familiar with metabolic syndrome, with laminitis and with insulin resistance. But the way I was saying, I think we need to get Dr. Macon to talk about this because we've just learned more. And so insulin dysregulation now encompasses more than just insulin resistance. It's the just things that we're continually learning. So, just the fact that insulin is not working in many different areas the way it should. So, that is definitely the terminology that is more accurately describing what's going on. And we encourage people to use that. But if they heard insulin resistance from their veterinarian or they read it, then we're talking about similar things.

 

Dr. Erica Macon (22:10):

Yeah. And fun fact, depending on the severity of disease, some horses may not have insulin resistance. They might just have what we say is hyperinsulinemia, they just have abnormal amounts of insulin circulating in the blood. And in order to test that, we don't actually test for tissue insulin resistance out in the field. We can, there's different type of tests for that. But oftentimes we just use a test for hyperinsulinemia because right now that seems to be the biggest worry when it comes to laminitis rather than tissue insulin resistance. But we can get into that.

 

Dr. Tania Cubitt (22:47):

So, I guess Erica, in the past when we talked about insulin resistance, we were just looking at elevated blood insulin and assuming, oh well they must be resistant to this in insulin because it's not going anywhere. When potentially they weren't. They just had hyperinsulinemia.

 

Dr. Erica Macon (23:04):

Yeah. And when we think about, when we first started looking into this metabolic syndrome and stuff, as we do with any type of research, we always look at what's been done in humans or maybe even companion animals. Because they're further ahead than what we're in for horses. And they started looking at glucose. And that for horses is not the case because they rarely have altered what we say is glycemia. So, blood glucose is kept in a very narrow range because too much glucose in different organs can lead to a lot of different problems. And of course, too low of glucose, which is a main fuel for all of the tissues of the body. If you don't have that, they can't function. So, then that narrow range is like roughly about a hundred. And horses don't have a problem with glycemia. They have a problem with insulin. So, it's very different from the disease that we see in humans and dogs and cats, they'll have higher levels of glucose because they can't even make enough insulin anymore and become insulin dependent. So, a lot of people do get that also confused because they are horses. Of course.

 

Dr. Tania Cubitt (24:16):

We as horse owners, take everything we learn from human nutrition and do it the best of intentions. Yeah. And try and apply it to horses.

 

Dr. Erica Macon (24:24):

Yeah. And we're still learning. Yeah. And I, I even my own research program at A&M, we're trying to use horses as a model for pre-diabetes in humans because it's before they have altered glycemia. And maybe we can look and see.

 

Dr. Tania Cubitt (24:39):

Maybe there's a marker that we can be looking for. That's you're in risk factor. Yeah.

 

Dr. Erica Macon (24:44):

Yeah. Or a mechanism. And my hope is that we can, while we're looking at this in humans, but we're also figuring out why it happens in horses.

 

Katy Starr (24:54):

So, what would you say is probably the most common misunderstanding from horse owners about insulin dysregulation in horses or all of that.

 

Dr. Erica Macon (25:03):

Yeah. The most common thing I run into is that they have to be obese. And that's not true. I see so many cases right now where horses have hyperinsulinemia or insulin dysregulation and they're very lean. I have a metabolic group of horses here at Texas A&M and one of them is a Mustang, his name is Monty. I love him, he's a good boy. But he, you know, you look at him and you're like, man, he's in great body condition. You might see a few little bit of ribs, but he doesn't have mass amount of regional fat. He just, he looks pretty fit actually. But he's got the highest insulins on the farm. And I think we're going to see that be more common in the future because I'm seeing it so much when I do consults with owners. In 2024, I was working with an owner and she had a 5-year-old and still extremely young, had averian cross.

 

Dr. Erica Macon (26:01):

And unfortunately that mare lost her battle to laminitis. But she was in great condition and you wouldn't think, at such a young age too at five, we were trying everything on the nutritional spectrum and even incorporated some newer pharmaceuticals that are really promising in this area. But nothing seemed to help her. So, I always tell people that just because your horse looks nice and healthy doesn't mean you shouldn't do some type of check-in or screening. I love preventative medicine. I spend so much money myself and my own animals. Because I have two corgis and a coli mix. And then I have the two thoroughbreds, which by themselves, my vet bills are always very high for them. But I love preventive medicine because we can get ahead of all of those things and if something just is slightly off from the previous visit, we may be able to detect something before something bad happens. And oftentimes people that have leaner horses that succumb to hyperinsulinemia-associated laminitis, they never knew that there was a problem until it happens. So, I always tell people, even if your horse looks normal, I always tell them to check in, get some preventative, run a resting insulin just to see.

 

Dr. Tania Cubitt (27:18):

It's something that Katy and I talk about always and any topic that we're talking about is knowing what your horse's normal is. Because that Mustang's normal is probably very different to another horse, to another horse. And because horses are like people, they're all going to be very different. But that brings up another very interesting point and maybe there's a question later on, but I think we should answer it now. So, generally the indicator that a lot of people will look for as like, okay, this is your risk factor, is your horse is getting overweight. Right? We need to be careful, but what are people looking for if their horse, what might be a symptom that something's not going right? If your horse looks otherwise healthy?

 

Dr. Erica Macon (28:11):

Yeah. And when we think about the classic, you know, obesity, like you said, that's, that's the thing for some horses I see that they just have regional fat. They're not overall, you know, you you they just...

 

Dr. Tania Cubitt (28:25):

Have some weird fat pockets. Yep.

 

Dr. Erica Macon (28:27):

Yeah. And sometimes that's above the neck on the crest. Because that's been, in research that's been one of the most highly positively correlated things with, when we talk about insulin levels, it, it's always a crest on the neck. And although you can't really classify it, but we sometimes horses will have subclinical laminitis where there don't actively show any symptoms, but there's changes happening within the foot. And you know, at some point those tiny changes become a really big problem. And that's why I always tell people, monitor digital pulses in your horse's feet, find their normal because you know, one horse's digital pulses are not the same as another. And I do that my metabolic horses here, and I mean the digital pulses is a big one, but even behavior, you know, a behavior is such a big thing. People kind of, they overlook it as being, you know, a sign of anything. But I've seen so many horses when they change their behavior, it's because something's wrong and you need to pay attention to it. Yeah.

 

Dr. Tania Cubitt (29:30):

And I think so many of our horse owners in the situation where they need to board their horses and then they rely on somebody else that sees them all the time to notice little things in the changes. But definitely, I think recently we did a podcast on, you know, temperature, respiration rate, digital pulse, vital signs. Yeah. So, that was something to have on the stall. These are my horse's normal, these are my horse's normal maybe after exercise if it's outside of this because I think that's really good and helpful if something is going wrong when a vet comes to say, okay, this is what the normal is. And then, you know, if it's slightly above that the vet can adjust. Or if it's way above that they're like, okay, something's real, real bad's going on.

 

Dr. Erica Macon (30:13):

Yeah. And I, even after something, you know, your horse has metabolic syndrome, I like to say, what is this horse's normal resting insulin or what's their normal post meal response? And because they're so, horses are so individual like humans that a single horse response will not be the, the same as somebody else. And that same horse, you may feed them the exact same thing, but a week later they respond. They're different. Different. And that's when it comes to evaluating statistics in any type of metabolic research study, it's so frustrating because there's so much variability and it makes it very difficult. But you know, that's one of the bigger problems in this area is because they're so different that it, it makes it difficult. But we love them all the same.

 

Katy Starr (31:07):

So, as we kind of go into this conversation, one of the things that we will be talking about is NSC non-structural carbohydrates. So, I think that's another thing that we should just briefly talk about a little bit. Just as a reminder for our listeners, if you haven't listened to this episode yet, episode 88, we did have a conversation with Dr. Duren very in depth about a lot of these non-structural carbohydrates, sugar starches, what all that means. But why don't we talk a little bit about how sugars and starches are broken down in the horse's digestive system? 

 

Dr. Erica Macon (31:42):

Yeah. This is one of my favorite things. I teach graduate equine nutrition at A&M and this particular lecture is massive for me because I love it so much. And the graduate students walk away and they're like, man, she really likes that stuff. . So, when we think about non-structural carb sensitive, it's a, you know, a collective term for both water-soluble sugars, ethanol-soluble sugars and starch. And when I say water and ethanol-soluble, we're just talking about simple sugars, you know, and then starch is just, you know, this branched component of just made up of a lot of sugars. So, these components are digested within the foregut or before the hindgut. Within the small intestine particularly. And this is a very complex, you never know how complex the GI is until you start digging a little bit more.

 

Dr. Erica Macon (32:39):

But when it, we think about the digestion of these particular nutrients, the body has so many different, not signals, but like cues for these because we want to try to digest them all within the small intestine before they get into the hindgut. And you have enzymes from the pancreas or an accessory organ that makes your digestive enzymes, it makes insulin, it makes glucagon, which is basically the counter to insulin. And these enzymes get released within the small intestine to help break down these maybe more than one sugar attached to another one gets, because you have to be able to have one sugar to go across the lining of the small intestine, which then after it gets past the lining, it goes within the circulatory system and it goes to the hepatic portal vein, which then takes it to the liver. Because the liver takes all of your, all of your sugar and all of the nutrients that you digest, it processes them and then sends it out to its respective like the muscle, the heart, the brain, all that stuff.

 

Dr. Erica Macon (33:43):

But so NSC is again just sugar and starch and this is digested and absorbed within the small intestine. And I know there was a note I thought when I was looking at the notes that I said in my review article that I can't remember the exact wording of it, but I said something along the lines of the foregut makes a really strong insulin or the only response when you think about insulin response, it comes from the foregut. And I was talking to Dr. Pat Harris not too long ago and she always reminds me of how little I know or things I forget and she was like, Hey, you know, after you left and went onto your postdoc, we started conducting more experiments that followed your other stuff. And she's like, interestingly, she's starting to do more stuff with long stem hay. And she said, Hey, you know, we're seeing a very similar response in regards to the insulin response after we feed long stem hay and stuff like that.

 

Dr. Erica Macon (34:48):

And that started to make me think about my comment in the paper we see and I kind of wanna, you know, change it just slightly, I think our biggest response comes from different types of cereal grains or commercial feeds that are digested in the small intestine because we make them so accessible for the GI. You know these, if you think about any type of commercial feed, most of those things are ground down and they're put into a small pellet form. You don't, when you think about the horse has to chew it just slightly, but most of those nutrients are very available. So, I think, and that's why I want to go back and say we horses digest those things really, really well because of the types of feeds that we have today. And that makes the playing field for a really large response.

 

Dr. Tania Cubitt (35:39):

And I think that feed manufacturers have done that intentionally because ultimately horses aren't meant to eat those things in any level, let alone high levels. But that's, when I say to people, they're also not meant to run around a track and have you ride them and do all the things that we love to do with horses. So, we as an industry have had to change the nutrients we give them. And I think the best thing that we can do is fully understand the digestive system, the digestive process so that we know when we're altering it. So, that then, okay, well what do I need to do to support? Okay if I'm going to feed them a lot more cereal grains, I have to process them, they're going to get a lot more starch in the diet. Is there something else I can add to the diet that's going to ameliorate some of the negatives that we know are going to come from that? You know, I think that the industry has done that intentionally, but the underlying factor is that horses were never meant to eat all of those things in large quantities. Yeah. We just had to make it safer.

 

Dr. Erica Macon (36:39):

Yeah. And myself and my colleague across the way, Dr. Sarah White-Springer, she's a muscle biologist and also a nutritionist by training. Her and I both are working on young course diets at the moment. And two of the graduate students that we have right now, they're going to present some stuff soon at Equine Science Society meeting. And it really focuses on the inclusion of higher quantities of cereal grains in these young animal diets. And what are the longer impacts of that, you know, down the road. Because you're right, they were never meant to consume this high of cereal grains in their diet. And actually, if you didn't know this, it's a fun fact. Horses have, they actually really, really suck at making an enzyme called amylase, which actually digest starch. And if you think about it from, you know, a just say basic level, horses are herbivores.

 

Dr. Erica Macon (37:35):

So, therefore they were supposed to be out foraging about eating different forages out in the wild, which roughly contain about one 1-2% of starch. So, they were never meant to eat that much starch in their diets. But then as the feed companies and our evolution of what we use horses for, you know, they have such higher energy demands with what, how we use them. We think about three-day eventersracing thoroughbreds, quarter horses, that it's that level of athleticism takes a lot of energy. And the only way to do that and to meet those energy demands is to feed them some type of commercial grain because it's condensed down and it's not a forage.

 

Dr. Tania Cubitt (38:18):

I do talk about amylase often, I've never used the word suck, but I will now because you said I could.

 

Dr. Erica Macon (38:23):

Yeah, . Yeah. They actually have a better ability to make lipase, which breaks down fat. And I always find that very funny because I'm like, where would they get that much fat out in forage? I don't know. But yeah, no, they really do suck at making amylase. 

 

Katy Starr (38:38):

So, another question that I had had was how did, because we talk about like less than 12% NSC is kind of that safety number for metabolic horses feeding metabolic horses. So, how did that number come to be? Where did that original recommendation come from?

 

Dr. Erica Macon (38:55):

You know, I focused a lot on this of my PhD. This was actually a paper done by Borgia and colleagues back in 2012- 2013, I can't remember what year. And they were actually looking at feeding horses, different levels of non-structural carbs in the form of hay. And this was in healthy and horses that had polysaccharide storage myopathy, which is a genetic disease where you can't break down and store glucoses, glycogen properly, all these things. And because PSSM horses are fed very similar to how we feed metabolic horses, that study said, Hey, it's literally like two lines in the discussion of that paper. It said if a horse is suspected to have metabolic disease or insulin resistance, you might want to not feed them more than 12% NSC in the diet. And we took that as gospel, but no one actually had done any work in metabolic horses to say that number was correct.

 

Dr. Erica Macon (39:57):

We just assumed based off of a different disease, even though they're fed very similarly. And that was actually the basis of, well like, my PhD was like, well let's put some science behind it. So, when I first got to Kentucky, it was May, I don't remember what year. And roughly about two weeks in, I started my first study, I hit the ground running. Like I said, I'm not smart, but I'm motivated. I was like, I'm ready to go, let's go. So, the first study, we were just wanting to see their post-meal responses from different cereal grains as well as we did some mixes of different things. But we basically had a ration balancer, a ration balancer with moderate protein. And then we did a mix of the, the moderate ration balancer, high ration balancer to see, because basically what we had was four different protein levels and only two NSC levels.

 

Dr. Erica Macon (40:51):

And some of that was really luck. I, I won't, I won't lie to you, some research is really luck. And what we found from that study was even the high protein ration balancer did make really high responses in these horses. But it wasn't necessarily because of the protein, it was because the, the threshold in that NSC was had been overcome. So, we really needed to figure out what was that level. And I set out on a year's journey with a Walmart coffee grinder in a lab with multiple different cereal grains and different formulations trying to make diets that actually only were different like 1% different from each other. Trying to set, tease out where that could be. And I did it for sugar and I did it for starch separately and then I'd hold the other ones constant and I held it as one protein concentration.

 

Dr. Erica Macon (41:53):

And there, when I was doing that particular study and I, I think I filled up a few composition books of my math because I would send off a diet to Equi-Analytical and I'm like, please, for all things holy let this come back right. And I finally, we got the good set of diets and we went on and we, we did these, this experiment where we fed a very small amount of it, roughly about, you know, one to two pounds just so we could have the same consumption rate from everybody and look at their responses. And I looked at them for 240 minutes after they ate. And we basically saw when those horses had sugar and starch that were above, now what we say is roughly about 0.1 grams per kilogram of body weight. We saw that their responses got elevated regardless of if it was starch or sugar.

 

Dr. Erica Macon (42:47):

But we also saw they were more sensitive to starch, which makes sense because one, they suck at digesting starch and two starch is made up of a bunch of little glucoses. So, as you digest more of it, you're adding more glucose within the blood, you got to get rid of it, which is only done by an insulin dependent pathway. So, those studies and, and there was a, a few pilots in between trying to figure things out before we ran those big studies. Those have left us with, okay, we need to move away from percentages. Because if you look at a bag of feed, any bag of feed and you compare it to a different one, there's different ingredients, there's different quantities of those ingredients. And we don't know how that affects horses right now because what I was doing was very controlled. I had a low NSC pellet and then I topped dressed on top of it pure sources of oat and cornstarch.

 

Dr. Erica Macon (43:44):

And when you think about pure sources, like it was a powder, I also, I hated measuring these powders because they were such small amounts. Those are readily accessible by the horse's gastrointestinal tract. They see them, they're like, Hey, I know what you are. We're going to adjust you real fast and absorb you. If you think about a pellet, it's attached to other things like those nutrients within are attached to something else. So, the body has to go through and start breaking that pellet down so it takes a little bit longer. So, we had that caveat in the paper that while we, we assumed that the, based off of all the results from those studies, that the new threshold for NSC is 0.1 grams per kilogram body weight. This was done with peer sources. But luckily we ran some follow up studies and there's still follow up studies happening where I actually used your Standlee's forage pellets.

 

Dr. Erica Macon (44:36):

And I found this same exact thing in that study. It was the same threshold if we kept that NSC at 0.1 or lower, we didn't see those exaggerated insulin responses. And I'll come back just a smidge. You don't want to have an exaggerated insulin response post meal in these metabolic horses because that higher insulin at the current moment, we don't know how often a horse needs to have a high insulin, the frequency in the duration before we induce a laminitic event. So, we operate under this very extreme bar that we want to keep it as low as possible all the time because we don't know where it's at. And there's a lot of researchers across the world that are trying to figure where it is right now. But this is our best recommendation thus far is that if we keep it under 0.1, we have a better chance of lowering those risks or likelihood of developing a laminitic event. And I can go into that Standlee pellet study if you'd like me to.

 

Dr. Tania Cubitt (45:41):

Before we get into that, I'd love to throw in a little bit. I think that the percentages came because number one, Americans don't use the metric system. Every research paper known to man on anything glucose and insulin, every researcher uses grams per kilogram body weight. And that body weight is also in kilograms. Nobody uses that. When I moved from Australia and I came to America, I had to learn pounds. And then I remember putting pounds in a scientific paper and they're like, what is wrong with you? We're metric. And I was like, oh my god, I, I don't know what I'm doing. I'm coming, I'm going anyway. But if you go out there and tell a horse owner, I need you to keep your diet at less 0.1 grams per kilogram,

 

Dr. Erica Macon (46:25):

Yeah

 

Dr. Tania Cubitt (46:25):

That's me looking over my head. They have no idea what you're talking about. So, we said, okay, well what does that kind of work out to be? 10, 12%? But it was also back when people were feeding a more standardized amount of feed to a horse in a day. It was about six pounds back 20, 30, 40 years ago. People fed about six pounds a day to a horse split over two meals, call it good. And now we've got horses that eat one pound a day. We've got horses that eat 2, 3, 4, 5 up to a senior feed with 18, 19, 20 pounds a day. So, it's one of those things where we need to do better, but the percentages are still the easiest way to explain it to somebody. And we haven't found the next easiest way. I'd like to tease out a little bit more, you know, when we label, because it's our general horse owners that are listening to this and when they go to the store and pick up is a bag of concentrate.

 

Dr. Tania Cubitt (47:27):

And they're going to, and I'll use the word concentrate because not all of them have cereal grains in them. And they'll look at that guaranteed analysis on the back. And AFCO, which is the American Association of Feed Control Officers, has some rules about what we have to write on there and how we write things. And there's if, if you are claiming that it is a low carbohydrate product, low NSC, you know, I'd love to talk more about the actual term NSC, but if it's low NSC, we have to write simple sugars, just your ethanol. So, carbohydrates, we have to write starch. But if it is forage-based, we also have to put fructan on there. Fructan being, you know, you can explain more about that. But you know, it's coming from some of your pasture grasses or forages that are included. It's even in beet pulp.

 

Dr. Tania Cubitt (48:16):

We're like why would there be fructans in this? There's only beet pulp. No fructans are actually everywhere. And so, then you look and a lot of companies will list just ESC and starch and if there's fiber in there, if there's forage in there, they're not. Right. You know, not everybody, it's kind of like the digestible energy story. Why nobody puts that on a feed tag. Because there's 15,000 different equations. We as an industry have not all decided this is the way we're going to do it and this is the way we're going to present it to consumers. And I think that until we get to that point, there's going to be so much that's just not quite right. But it's the best we have. You know, people will come to me and say, oh my God, I can't feed that, it's got X amount of NSC in it.

 

Dr. Tania Cubitt (49:04):

I'm like sweetie, it's an ounce of an electrolyte supplement. If it was pure sugar, your horse is probably going to be fine. Because oh by the way, he doesn't have metabolic syndrome anyway. But we as an industry have decided that every horse needs to have a low carb product. So, anyway, that's just me on my soapbox because we've done that though. We you know, I was in the Dr. Hoffman, Dr. Kronfeld original. It was fat and fiber and sugar and starch. And that was what the world revolved around. And it was glycemic index and should, and obviously now all the terms have changed. But you know, we said every horse should be on fat and fiber and no horses should eat sugars and starches anymore. And then I got into the real world and decided, oh well there's going to be no racehorses ever again.

 

Dr. Erica Macon (49:47):

And we go back and forth with some people about like, these animals are very athletic and you're asking them to do lots of stuff. They need sugar, they need starch, they need all these things. Not every horse NSC is bad for. Because the problem is, if you don't use that NSC, you're going to store it.Somewhere else. And that's when you run into problems. If they don't need the energy, don't, don't feed it to them. 

Dr. Tania Cubitt (50:12):

I am so excited that you're on. I feel like we might have to break this podcast into two, Katy. Because I could just talk all day long with Erica. But anyway, yeah, that's my 2 cents on the dang percentages. Because I hate them too because people will say to me, well, you're telling me it's got, you know, 15% NSC or protein or whatever it might be. Is that in one pound or is that in the whole bag? I want to say, Hmm, let's just go back to elementary school math and percentage means nothing unless it's attached to an amount. I always say, you, I'm going to give you a hundred percent. Katy, tell me yes or no.

 

Katy Starr (50:50):

I don't know of what hundred percent of what.

 

Dr. Tania Cubitt (50:52):

Exactly. I will give you a hundred percent of my salary or I'll give you 1% of Bill Gates's salary. And I guarantee you, if you said I want a hundred percent, you're a loser.

 

Katy Starr (51:03):

. That's such a good perspective though. Yeah, yeah,

 

Dr. Erica Macon (51:06):

Yeah. Yeah. That's the problem. As scientists, you know, teachers, we have done a really bad job at disseminating and really saying, what does this mean on a practical perspective. So, when I wrote that review paper for the American Association of Equine Practitioners meeting, I thought to myself, I was like, it's really hard for an owner to look at grams per kilogram of body weight. Like what is that to, like you said to most owners, what is that? They're like, what is that gibberish? You know? And I'm like, but you know, who does use the metric system, veterinarians. And so I was like, what if I give them calculations and they can help the owner. Which is why I included those, those calculations in that paper. And I went through, and I also, you know, listed some very common somebody, some of your biggest feed producers, you know, and they were marketed towards metabolic horses. And you're, you can feel free to share those graphs with your listeners if you want to, but it just showed that not all low NSC feeds actually have low NSC. And maybe if you compare that low NSC feed to a performance feed, heck yeah. It's got lower levels because most of our, we think about like commercial NSC levels, they can really range between 20 and I've even seen some higher and closer to 40%. And again, for those horses that need those feeds, they need that stuff because.

 

Dr. Tania Cubitt (52:38):

I don't think there's a really a rule in labeling. Like you could put lower NSC or low starch on anything. It's very difficult. It's hard. And that's why we encourage our listeners to have a relationship with either their feed sales rep or their nutritionist or their veterinarian. Because you don't need to know everything.But you're dang sure. Better have a good team of people that you trust that you can ask those questions to. And look, you and I just said the same thing, we have a PhD, but we have people that we bounce ideas off all the time. We don't know everything.

 

Dr. Erica Macon (53:12):

No, no. I'm the first one to admit that I don't know everything. And I, for sure when I , I think to myself, oh, do I not know that? And then I'll text what I now call her is Mama Hoffman . And I'll say, mama Hoffman is this right? She'll send me a text back and she'll have like an emoji of like a thinking face. And I'm like, you don’t know?!

 

Katy Starr (53:33):

.

 

Dr. Erica Macon (53:33):

So, yeah, you have to have more than one mind on this, especially for such a complicated creature. You know, it is horses because of the way their GI tract is set up and just them in general. It's always best to have a team lead the health of that horse. I think the same way in science. I would rather have a team of scientists trying to tackle a question than just myself. Because those different perspectives, and just the perspective itself is so helpful.

 

Katy Starr (54:04):

Yeah.

 

Dr. Erica Macon (54:05):

But yeah. Sorry, we're getting off on a tangent.

 

Katy Starr (54:07):

No, I mean, that's great though because you never know something that you're not going to think of. It may be somebody else will think of. Oh yeah. If that missing link sometimes, I mean that it's so valuable.

 

Dr. Tania Cubitt (54:19):

Have we shown people in our show notes before? Like I talk about it all the time. You know, the mineral thing that looks like a big spiderweb. It really,

 

Katy Starr (54:28):

We talked about that on one of the episodes. Yeah.

 

Dr. Tania Cubitt (54:29):

I feel like we have. But it's just like a circle and it's got all the minerals around and it shows all of the cross connections. And it's this giant messy spiderweb. And you can use that analogy for pretty much everything in horses, whether we're talking about the sugars and starches that are in the feed. Well then what about the management? I fed this amount of sugars and starches and I broke it up into 10 meals a day, or I fed it once. Like everything is all so interconnected and we hyperfocus on one thing. And that I think is the worst thing that people do, is hyperfocus on one thing. And forget about all the rest.

 

Dr. Erica Macon (55:09):

Yeah. A lot of science does that. They'll focus on one thing, but then the best science is the ones that come back and say, why does this matter?What are we looking at? Yeah.

 

Katy Starr (55:21):

Yeah. No, that's excellent. If you thought this was interesting, stay tuned for part two of our interview with Dr. Erica Macon releasing Tuesday, June 17th. In this next episode, episode 96, Dr. Macon shares the results of how Standlee pelleted forage impacts insulin levels in metabolic horses. We also chat about potential feed management ideas that could help metabolic horses. And we discuss how and why horses might get laminitis in the winter. You won't want to miss this next episode. 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.