Transcript:

[0:04]

Welcome to this video podcast asking the question: does exercise negatively impact reproduction? And to start this off — this is in horses. So this is not meant to be medical advice for women. But what we know in exercise and effects on reproduction — much of that information has actually been done in humans. So it has been looked at in males and females. Now we are looking at some of that impact on other athletes, like the horse, and that is the whole purpose of this discussion: to look at the impacts that exercise might have on reproduction in the mare, particularly, and then maybe the stallion — and we'll save that one for the end.

[1:02]

So what is the genesis of this — asking the question: can exercise impact reproduction negatively? And as a young PhD student, when you start off in your career, you’re hoping to contribute to the field of science, but don’t really expect your research to have much of an impact — especially early on in your career — because you look up to those old professors, those mentors that I’ve had through the years: Dr. Anne Rodic, Dr. Martha Vogal, many others that have impacted me in my career. And you hope one day to equal them.

[1:48]

And so this genesis of this research actually started with Dr. Vogal when I showed up to Texas A&M as a bright new PhD student — ready to go, aggressive, wanting to learn as much as possible. I had a very keen interest in embryo technologies — these advancements that we’ve been making in cloning and embryo transfer, oocyte transfer — all of these techniques that we now use in the modern-day breeding barn with our horses, and in many different breeds and disciplines.

[2:28]

And Dr. Vogal, when I showed up, told me she had the perfect project for me — and that was heat stress in mares and impacts on reproduction. Her husband, Steven Vogal, was a broodmare manager — or a farm manager — at a very large embryo transfer facility in central Texas. And embryo transfer — and this is early 2000s, so 20 years ago — but embryo transfer in the late 90s going into the 2000s had become more of a technique horse owners were using for their mares.

[3:05]

And the reason for that is because the AQHA — which is the large breed organization in the United States, the American Quarter Horse Association — and there’s over four million quarter horses around the world, millions in the United States — their breeding rules used to be that a stallion could breed as many mares as he could throughout the year using artificial insemination. So theoretically — stallion produces billions of gametes — you could produce as many foals as you could on that one stallion, and then you could come back and register that foal to that stallion.

[3:47]

So typically some of these stallions had hundreds of foals — the very top ones — registered to them. Whereas mares could only have one per year. Now genetics — 50% of the foal is the stallion, 50% is the mare. The mare is just as important in the genetics of that foal. And so it was a bit unfair to the mares. They could produce some top foals for good money for a lot of these horse owners, but yet they were restricted.

[4:24]

Now there was a lawsuit — don’t need to get into all that — where the AQHA did open up their rules to where the mares could breed and produce as many foals as they could per year using embryo transfer.

[4:44]

Now, to back the bus up a little bit — embryo transfer is: you generally artificially inseminate the mare, then she ovulates, and then fertilization takes place within her. And then at day seven, you can go in and flush her uterus and get the early embryo — which is just a big clump of cells — and you have to look with a stereo microscope to find them. But then you can take that early embryo — it’s spherical — and then transfer that into a recipient mare. And the recipient mare can carry that pregnancy to term, nurse the foal, raise the foal, and then wean the foal. But that foal’s genetics go back to that stallion and the original mare who donated her egg and was fertilized.

[5:27]

So that allowed embryo transfer to grow rapidly in the last few decades in the horse industry. And I just use the AQHA as an example. Now the Jockey Club — for racing thoroughbreds — it still is all natural. There is no embryo transfer going on there; it’s not allowed by their breeding rules. But with our mares, we can push them a little bit reproductively, and on average, mares can maybe produce four foals a year. You don’t want to push them too much — they still have to cycle, and you still need to go in and flush their uterus — so you don’t want to do that too much within a year.

[6:11]

And I know there was a record — I was at a meeting in Argentina — where they got over a dozen embryos from a mare in one year. So that was really pushing her hard. Typically we do about four, and then we’ll let her rest until the next breeding season. But that has allowed embryo transfer to grow.

[6:30]

So going back to heat stress — and Steven Vogal — he had noticed that mares in late spring, early summer in central Texas, where it gets really hot during the day, were producing fewer embryos. And they were also of poorer quality. Now, to caveat that a little bit — and we didn’t know this at the time — but he thought it was more of a heat stress issue, because we do know heat stress, which we covered in a previous podcast and video podcast, can negatively affect reproduction in other species — cattle being the big one.

[7:09]

So Dr. Pete Hansen — he was one of my colleagues at the University of Florida — is well known around the world for investigating heat stress in dairy cattle and their negative impacts on reproduction. So, before I even went to Florida, I was involved with reading a lot of his research when I was setting up my PhD dissertation work.

[7:35]

With embryo transfer, the other benefit for these mares is they can continue their competition schedule — still train, still be ridden, and go out and compete. So you have some broodmares that are just broodmares — they’re done competing, they’re just producing foals and are involved in embryo transfer. Then you have these competition mares that, in their competition careers, can produce embryos and produce foals through embryo transfer.

[8:08]

So we didn’t know at the time — we didn’t know if heat stress impacted horse reproduction, and we didn’t know if exercise could impact reproduction. But Steven Vogal said there’s something there. And then Dr. Katrin Hinrichs, who I worked with at Texas A&M — world-renowned, heavily involved in horse cloning, incredible mentor to me — she also said, “Yeah, there’s something here.” And she came onto my committee and helped me through this project with Dr. Martha Vogal.

[8:40]

So we started to look into heat stress in horses. Now, horses — as we talked about in the previous podcast — they can suffer heat stress in really extreme conditions. But generally, as long as they have shade and water, they thermoregulate pretty well during a hot summer day. When you drive around and live near livestock, you can see cattle ruminating under the shade, typically, and horses out there grazing in the sunshine. Because they can go — if they get hot, they’ll go to the shade, or they’ll go drink some water and cool off. They’re sweating a little bit, but generally they don’t get too hot.

[9:27]

When we looked at setting up this experiment — or the series of experiments that we did — we thought, okay, if we really want to heat-stress them, we’re going to need environmental chambers. And there’s a lot of concerns with putting horses in environmental chambers. But we didn’t have them at Texas A&M, and there are welfare concerns with putting horses in something like that. It is done — there are things like oxygen chambers that people put horses in for healing and other purposes, so it’s not something new to the horse industry — but when we looked at doing environmental chambers, we decided no, that’s not our best option.

[10:12]

And again, we’re doing scientific research under veterinary care with permission from the Animal Use Committee at Texas A&M — that’s a completely independent organization that evaluates any animal research. If there’s any stress or welfare concerns, you have to address it. And if there is, as part of the experiment, you have to really argue why you need to do this experiment — and a lot of times you can’t. So at the university level in the United States — and I know in many parts of the world — animal welfare is a top concern. Okay, so I just wanted to put that there.

[10:52]

So the next question was: okay, how are we going to get these mares hot? In the other podcast with heat stress, I cited the G.E.A.R. study — that was the basis. I remember reading that study and going, “Aha! Here we go — this is how we can elevate body temperature.” That study was Heat Storage in Horses During Submaximal Exercise Before and After Humid Heat Acclimation. So when their horses were exercised between 90 to 92°F, 85% humidity, after 20 minutes their core body temperatures spiked to 106.7°F, which is about 41.5°C. That is super hot.

[11:37]

And a few of my horses got in the 106 range when I did my study — which I’ll talk about — but not that hot. We didn’t typically see them get that hot because Texas, in the summer, humidity varies throughout the day. Generally it’s higher in the morning because the moisture is in the air, but by mid to late afternoon in Texas, it’s mid-humidity — about 50%. Still hot, very hot, but not quite as humid as somewhere like Florida, where a rainstorm will come in, dump a bunch of moisture on the ground and in the air, then the storm goes off and it gets up to 95°F and is really humid because the sunshine is evaporating all that moisture into the air. That’s the humidity part.

[12:24]

Well, in central Texas — College Station — it’s more dry. So I did approach my committee and said, “Okay, I think we can spike the temperatures in these mares by exercising them.” And we know heat is a byproduct of exercise. So it wasn’t really a heat stress study — effects on reproduction — it was more exercise stress under hot and humid conditions, or hot conditions, maybe not humid all the time. I mean, 50% humidity, 60% humidity — you could argue is still pretty humid for certain parts. But the idea was exercise stress.

[13:11]

And when you look at — or hypothesize — “Okay, I’m going to exercise these horses, I’m going to spike their body temperature,” in my head I’m thinking, am I going to cook that early embryo? I mean, you’re talking just a few cells to a few thousand cells. Now, the horse’s body is trillions of cells. Early embryo development — you know, it’s a single cell first day, then two cells, then four cells, then eight, sixteen, because they’re dividing — thirty-two, sixty-four — day three, day four, then you get into the blastocyst and you have thousands of cells. It takes a long time for that horse to get to the trillions of cells.

[14:00]

But I thought, okay, if we heat stress them, maybe we’re cooking them. Or the oocyte from the mare — her egg — gets damaged due to body heat, or the sperm cell from the stallion after insemination and exercising her — maybe that’s contributing to reduced fertility. Because again, this idea that heat and then the exercise could reduce fertility.

[14:32]

Now, also — what I talked about in the heat stress video podcast — when a horse is exercising, and even us, blood is shunted away from the core. Because the core is where the muscles are working, the heart’s working — you’re getting the muscle byproduct, which is heat — and blood is shunting to the extremities to cool the horse off. So the body is going through some stress, and in that fight-or-flight mode — because that’s what exercise is: flight, right? It’s kicking in the stress system of the horse, and it’s shunting blood away from the digestive system and from the reproductive system.

[15:20]

The last thing a mare wants is to be reproducing if she’s stressed or running for her life from a wolf or something in the wild. So it makes sense that the body is set up that way — reproduction is one of those things that starts to go with stress, especially chronic stress. Acute stress you can overcome relatively quickly; it’s the chronic, day-after-day-after-day stress. Which a broodmare that is in a competition schedule, in a training schedule, is going through — those daily stressors of being handled, being groomed, being tacked up, going through stress to train and compete. That’s like our prime athletes in humans.

[16:08]

So when you start to divert blood away from the reproductive tract, you are diverting energy, nutrients, oxygen — hormones, critical. Because whenever I talked about reproduction — and again, my PhD is in reproductive biology — I always describe it as a series of carefully orchestrated events. To be successful, there has to be step one, step two, step three, step four, step five, in all these different orders, to be able to get a mare to conceive a foal.

[16:46]

So the mare has to develop follicles on her two ovaries — without getting too much into reproduction — but that takes hormone signaling plus nutrients. And then, as you’re going to see in a follow-on study I did, blood flow to those follicles that are developing on her ovaries that house the eggs. And then she’s going to ovulate one of those — and that’s hormone signaling. Then the oocyte travels down into her oviducts — or the fallopian tubes, which you may be familiar with — and the sperm cell needs to be there to meet it.

[17:22]

The ova has about eight hours after it’s ovulated — you roughly have about an eight-hour window where it needs to be fertilized, or it’s done. It just dies. And then once you get fertilization, you have a one-cell embryo — very, very sensitive — for about 24 hours. And then again it goes through that two, four, eight, sixteen, thirty-two, sixty-four cell division over the next following days. And there needs to be oxygen in the reproductive tract, nutrients, and it has to be in an appropriate temperature — because if it gets too hot, it can injure those cells or kill those cells, and then the embryo is no good.

[17:59]

So that is what we were hypothesizing. And then when you look at the hormone signaling — the brain’s releasing stress hormones — well, typically the brain’s releasing what we call FSH or LH, which are signaling hormones for the mare to develop follicles and ovulate. So when the body’s stressed, those hormones are impacted — they’re not released as much or in as great a quantity. The stress hormones are, and that’s what the body is responding to.

[18:37]

So you have all of this competing with the body to keep the horse alive. Right? That’s the whole purpose of the stress response system — to escape predators or survive whatever stress it is — and then heal and overcome. And that’s what training does, that’s what exercise does. And then with heat too — heat also can stress the horse, as we previously talked about.

[18:57]

So that led to this project that we set up. And my committee was — obviously — Dr. Martha Vogal, I had Dr. Katrin Hinrichs, I had Dr. Dewey Kramer — who’s like one of the grandfathers of embryo transfer. He was the big cloner in the early 2000s. Dewey — the deer was named after him — the first cloned deer. CC, “CopyCat” the cat — that was his — lived a full life, that cat did. I had Dr. Nancy Ing as a geneticist, Dr. Youngho Choy — who was the ICSI guru of the world in the 2000s — that is in vitro fertilization for the horse, whole other podcast, different topic.

[19:48]

So I had a really robust committee guiding me, and some incredible people that I got to work alongside with. They set me off in my career. That resulted in my first published paper in 2009 titled “Embryo Recovery from Exercised Mares,” and — I love that paper — because I didn’t realize that research would have such an impact on the industry. As a PhD student, you just never did.

[20:14]

All right — so how we set this up. We were going to exercise the horses in early afternoon. We had a mechanical exerciser — so, there’s mechanical hot walkers, if you haven’t seen them. They have a series of gates, and you can set them, and it can push the horses to a trot, light canter. I would say our exercise was moderate — it wasn’t strenuous. We weren’t pushing them too hard. And we did it for 30 minutes, and then we had the cool down — which I talked about in the previous podcast — had a couple horses come up heat stressed. We cooled them down with hoses, walked them, and we would never return them to pasture until they were properly cooled down.

[20:58]

So this wasn’t extreme. The average temperatures over the study of the two years I did it was 86°F, about 30°C, and about 50% humidity. So this wasn’t extreme. And again, we monitored those horses very, very carefully — we checked their temperatures all the time during exercise, after exercise, and then after that cool down period. Again, they would not be returned to pasture until those temperatures were getting back close to baseline.

[21:29]

So I think that’s what you’ll find interesting — this wasn’t extreme, this wasn’t heavy or very heavy exercise for the horse. These are broodmares — they were given training before this to be fit, so they were fit — but these weren’t competition horses. Now, we artificially inseminated them, and then on day seven, I went in to collect an embryo.

[22:00]

And Steven Vogal taught me, with Dr. Katrin Hinrichs on my method — I would go in and you set up a flush media that’s commercially available, that goes through tubing into the uterus of the mare, which has a balloon at the tip of the catheter which creates kind of a vacuum in there. And I would put 500 milliliters in there, I would go in and massage that up — because the mare has two uterine horns, and you don’t know where the embryo is at day seven if it’s in there — and then drain it. It goes through a tube into a collection dish, which has a 75-micron filter so the embryo wouldn’t go through but the fluid would.

[22:44]

And we would drain that out — and I did that four times. Then I would take that into the lab, put it in a collection dish, and look for that embryo if there was one. Now, typically in embryo transfer, you would take that embryo and go and put it in a recipient mare. Our embryos were used for genetic analysis to look at any damage or heat stress that may have been experienced, in a later-on study.

[23:10]

But I did this over two years, and again, the results were really striking. We just didn’t expect it, didn’t anticipate it — and, you know, again, I go back to my mentors at A&M. Just to give you an idea of how hot these mares were getting in exercise — in that paper I published, the initial temperature was on average 37.9°C (about 100.2°F). And then their final temperature, post-exercise, averaged 39.5°C (about 103.1°F), with some mares going as high as 41.28°C (106.3°F) — and that was just a few of them. Most of them were in that 103 to 104°F range.

[24:11]

Now, when you do this research, you look at all the data you can. And this is what I found really interesting — I remember the day doing this, too. I was in my apartment, and you know, all the statistics, and you do all your spreadsheets, and then I started looking at averages. And I’m looking at every little thing I could — and I remember when I found this data, I was like, “Holy smokes, this is incredible.”

[24:35]

So, our horses that were exercised had a delay to ovulation, and they ovulated smaller follicles. Okay? So when you looked at their ovulatory period — from ovulation to ovulation — our horses that were exercised, their follicles did not get as big, and it took them longer to develop. And the hypothesis is: because of stress, that disruption to the hormones, it took longer for that mare’s reproductive system to ovulate.

[25:16]

And you can hypothesize a whole bunch of different things — I have a little bit more data that backs up a little bit of this thinking — that oocyte that’s ovulated is probably not a great quality oocyte, because it has to be properly matured in that follicle. It grows, it gets this cumulus layer, it needs the nutrients, it needs the oxygen before it’s ovulated — and exercise appears, based on just this data, to be delaying that process. And then the follicles, when they ovulated, were smaller.

[25:53]

So that was really striking data. And human research has corroborated some of this — it is well known that extreme female athletes have disruptions to their cycles. They may not cycle for months. There’s a lot of other things too — they think with body fat composition — but that strenuous exercise is definitely impacting it. So we know there’s something there, that exercise is impacting the female reproductive cycle. And then we see it here in horses.

[26:26]

Now, to get to the big data — the horse embryo transfer data over the two years. In essence, we cut their fertility in half. So my recovery rate of non-exercised mares was about 63% — that means six out of ten embryo flushes I would attempt, I would get an embryo. And that’s average. Average is anywhere from 50 to 75%. You know, Steven Vogal saying, Katrin Hinrichs — who’ve done this for years — they’re three out of four, they’re getting an embryo. Chris — six out of ten, or three out of five — is getting an embryo. And again, that was my first time doing it — I did a few practice sessions, but then once we started the study, that was the number.

[27:25]

When we looked at the exercised mares, we went from 63% down to 34%. So again, just a little over three out of ten times on an exercised mare, I would get an embryo. So again, cut their fertility in half.

[27:44]

What else was really striking — and really exciting, and nerdy, and I’m sorry if this gets a little nerdy — but it is really like the miracle of life, that’s why reproductive physiology is so incredible — the embryo grading. Okay, so an embryo quality grade one: perfect embryo, no imperfections, beautiful — they’re just so beautiful under a microscope — wow, that’s the one we want to get, we want to transfer to a mare. Embryo quality two — okay, you have a few little, they call them extruded cells — these are cells that died, and the embryo is really good at getting rid of those, so on the periphery you see this little black mass. Embryo quality two — they’re okay, you can still transfer them. Embryo quality three — wow, something’s not going right, half the embryo’s dead. So half the cells are black and dark, half the cells are viable — you’re like okay. And then grade four is pretty much a dead embryo — black throughout.

[28:46]

Now, in our non-exercised mares, about 75% were embryo quality grade one, and then 5% grade two, 10% grade three, and 15% grade four. With the exercised mares — again, this is where the data was striking — I got fewer embryos, cut in half, and then a third were quality grade one, just under a third were quality grade two, and then a third were quality grade four — just black, dead, nothing there.

[29:17]

So that made waves — popular media picked it up, had some press articles written about it. When I went and presented it at a conference, Professor Twink Allen stood up and said, “Young man, that was a beautiful presentation,” and I was like, “Wow.” You know, he’s one of the grandfathers of horse reproduction. It hit me — wow, my PhD dissertation made waves.

[29:44]

And then — I tell this story — at a conference a few years later, I had a veterinarian from Germany very upset at my research and challenged me on everything. I was really taken back. It was the first time anybody challenged me on this research. Everybody was so interested in it, and I just wasn’t prepared. Again, I was still a young professor. And in reflection, I realized I was probably hurting his business — because this had made news around the world, especially in the horse world — and he did a lot of embryo transfer in competition mares. The owners were like, “Why am I paying you this money? We’re not going to get an embryo.” So he was starting to lose some business. So he was a little upset.

[30:29]

Now, one study doesn’t make a truth — I preach that all the time. And I did have some other independent labs around the world try to repeat some of this — they saw the same phenomenon. And then I went off to Clemson for my first professor job and repeated this work.

[30:49]

So I did a follow-up study with Dale Kelley — he was my first graduate student. He’s now Dr. Dale Kelley — he did his PhD with me at the University of Florida, then he went and got his DVM, and now he’s a professor at Oklahoma State University. Brilliant, brilliant person — just incredible. So smart and driven. I was just blessed to have him as a grad student.

[31:14]

But in his master’s work, I said, “Okay Dale, we need to look at the hormones — because it’s something I didn’t look at in my dissertation work. We think exercise is having an effect on reproductive hormones.” So we went and repeated the experiment — but we were exercising them in the cool morning, not in the hot afternoon. South Carolina, around Clemson — that’s upstate — it gets warm in the summer, but not baking like Florida or Texas. It was warm, but we just kind of wanted to remove that element of heat and just keep it at exercise, and do what horse owners will probably typically do, and that’s train in the mornings.

[31:57]

And again, when we went back and looked at the data — exercised mares had longer cycles, they had delays to ovulation. Then when we looked at hormones, the one hormone that stuck out the most was luteinizing hormone. That spikes with estrogen as the mare gets ready to ovulate — that’s the one responsible for ovulation and then for some other things after — but that’s the one that helps really mature that oocyte. That was lower in our exercised mares.

[32:32]

So we published that work — “Exercise Affects Both Ovarian Follicular Dynamics and Hormone Concentrations in Mares” — in 2011. I think that was one of Dale’s first papers, and it just was a very, very exciting study.

[32:44]

So then I did another study after that, and this was with Rachel Smith. She was doing her master’s with me — great student, very hard worker — and we wanted to repeat what I did in Texas, but she was doing the embryo collections. We were exercising them in the middle of the day — so I wanted somebody not me doing the embryo collections, an independent somebody else — so she was doing all of that.

[33:15]

The middle of the day temperatures — again, 25 to 30°C, 77 to 89°F, humidity about 50% — so again, not very hot or very strenuous. But I introduced Doppler ultrasound. Now, for some women that have gone on to, or some of you listening that maybe you’ve gone to ultrasound scans in humans during pregnancy — and they show you while they’re ultrasounding, they’ll push some buttons and you see some blue and red of the blood pumping — it’s pretty common today across the world. Doppler ultrasound back in 2007 and 2008, as far as livestock use or in horses, was a real new technology.

[34:04]

Doppler ultrasound — I was able to purchase a handheld unit — and what we were looking at was the blood flow around the dominant follicle. So again, without explaining too much reproduction: as the mare’s ovaries generate follicles, they generate multiple; there becomes one that becomes dominant, and that’s the one that’s going to ovulate her oocyte. Well, there’s a lot of angiogenesis — so, if I use that term, it means a lot of vessels growing in that follicle to pump the nutrients, pump hormones to that fluid that has the oocyte, or egg, in it.

[34:44]

So it’s called angiogenesis — the generation of blood vessels growing there — and you can see this on a Doppler ultrasound. With a dominant follicle, you can see all the blood pumping around it. And so, I was curious — okay, well, we know from Dale’s study and my study that maybe we’re disrupting that blood flow to the follicle, and that is having some impact on why I didn’t get twice the same amount of embryos. Because that’s where you might see an impact — is it the oocyte, or the early embryo? Where is that breakdown happening in these exercised mares? Is it poor oocyte quality, or is the embryo dying really young and we just never see it?

[35:42]

So — sorry, that gets a little into too much of the repro side of it — but to kind of explain this, let’s get to the results. Again, very exciting. So Rachel — her recovery rate was 67%, so a little bit better than mine (but I trained her, so I can take some credit — no, she did a wonderful job). 67% of her embryos recovered from control mares were 93% quality grade one, and then only one embryo — 7% — had a quality grade two.

[36:19]

So to me, that says either different mares, different genetics, or maybe that heat in Texas had some impact, because it was hotter there. Then we went to full exercise — 67% down to 43%. So, not quite as drastic as mine, but a significant reduction. So you did see that reduction. And then, her quality wasn’t as bad either — it was 78% in quality grade one, 12% in quality grade two, and then she had some unfertilized oocytes that she collected.

[36:58]

So overall, looking at that, there was an impact — it just was not as drastic as my PhD work, which we could explain by saying these mares weren’t exercising in hotter or more humid conditions.

[37:09]

But again — and then we took pictures of all the embryos, it’s a really good study — “Impacts of Moderate Exercise on Ovarian Blood Flow and Early Embryonic Outcome in Mares” — that was in the Journal of Animal Science in 2012.

[37:23]

And then when we looked at blood flow — that was really exciting. Our control mares, their dominant follicles had really good blood flow around them. And then our exercised mares had really poor blood flow around their follicles. And then we did some correlation statistics that showed, yeah, if there was greater blood flow around the follicle, that usually meant we would get an embryo that was good quality. And again, that’s contributing to the field of reproductive medicine and technologies in horses.

[38:04]

So the take-home message of all of that in horses — okay, again, that’s where the popular press picked it up: “Oh, could it impact women?” You can’t design an ethical study in humans to measure exercise and then flush embryos from a woman to see if she would get pregnant. There are studies out there looking at exercise in women during pregnancy — early pregnancy, mid-pregnancy, late pregnancy — speak to your physicians if you are exercising and wanting to get pregnant, or you are exercising and pregnant. Because again, I can’t speak to that — there is a lot of research in that area.

[38:51]

I can speak to horses, and I can say — because I’m probably the world expert in this field — exercise in early pregnancy can be detrimental to the mare. Period. End of story. And it’s not just my research and research we did at Clemson University — other independent laboratories around the world have done science, testing at universities — they’re seeing the same phenomena. Many veterinarians that work in embryo transfer around the world have seen the same phenomena. So it does impact their cycles, and it does impact that early embryo’s ability to survive.

[39:24]

So generally, what I would tell horse owners or people is — if you are trying to breed them during those days leading up to ovulation and post-ovulation — very light exercise, do not push her, and let her rest a little bit. And I think that would help improve your chances of getting an embryo. But again, I haven’t done that study, and we’d have to follow it up with some research.

[39:46]

Okay — what about the boys? Get to the end of it — the boys are fine. Those testes thermoregulate just fine. Dr. Vogal and Dr. Clay Cavender at Texas A&M did some follow-up studies — I remember Dr. Vogal told me they did a study where they put diapers on the stallions to try to raise their testes’ temperature — it had no effect on their parameters when they went to collect them. Sperm cells were fine, counts were fine. Those testes do a really good job of keeping them cooler than body temperature.

[40:27]

Because remember — cryptorchids, that’s when both testes are in the abdominal wall of the stallion — they’re infertile because the testes are at body temperature, and sperm cells can’t be produced. That’s why they’re external — they’re cooler than body temperature — and they do it just fine. So, no impacts there.

[40:47]

The final study I want to talk about — and this is Dr. Jason Anton, now he was one of my master’s students, and he went off to get his DVM — was exercising the pregnant mare from day 16 to day 80 of gestation, just to see if there’s something there. And we published this in the Journal of Equine Veterinary Science in 2014.

[41:09]

We wanted to see if there were some impacts on reproduction. Again, we were using Doppler ultrasound, looking at fetal measurements — because, again, the research in humans shows that women can exercise during pregnancy, as long as it’s moderate to light, and there’s usually no adverse outcomes. Horse owners can exercise their horses until the mare gets a little bit later in pregnancy, and then they’ll probably let off or completely stop it. So that’s why we wanted to look at this and see if we noticed anything.

[41:45]

And no — everything was fine. All mares went on to give healthy foals. The only thing that we found interesting was the mares had lower progesterone levels, which is important for maintaining pregnancy. But again, all these mares went on to deliver healthy foals.

[42:04]

But we did notice that the foals were actually growing larger in utero. We were able to do some transabdominal ultrasounds and look, and I think we also did some transrectal ultrasounds. We measured the fetal length and fetal size, and these mares that were exercised — their fetuses were growing a little bit bigger. So maybe there was some good blood flow going on, maybe exercise, staying fit, was healthy for the foal. That’s what we kind of supposed — it wasn’t detrimental at all, we didn’t see anything detrimental — but maybe it was a little bit healthier in stimulating some growth in that.

[42:45]

Again, we need more follow-up research, but it was very interesting work. And, you know, just to kind of tie this all up — it’s something that I think you need to discuss with your veterinarian if you are looking to do embryo transfer in horses, or whoever you’re working with in the breeding barn to breed these mares.

[43:09]

My advice again is, if they are in a training program or competition schedule, try to schedule when she’s going to ovulate and those early days of the embryo so that they either rest, or you go very light for her. We can manipulate the mare’s estrous cycle relatively easily. We start with lights in the winter, and then we do have a lot of pharmaceutical drugs — we can short-cycle them, cycle them, we can prolong their cycles — so there is some way to manipulate it to a degree.

[43:46]

So, if you do have a big competition that you won’t miss, maybe after she gets back, you kickstart her cycle and try to get an embryo out of her. I would argue we need to keep researching this, because the mare’s genetics are just as important as the stallion’s — they’re critical to the longevity of our horses, the health of our horses. We want foals that can withstand the stressors that are placed on them as they grow and go into competition, and we want these horses to live long and happy lives. And the mare’s genetics are a critical part of that. So we need to find ways to keep their genetics flowing throughout our different breeds of horses around the world — and embryo transfer is one of those ways we can greatly increase that.

[44:49]

So — very interesting research, loved it. Again, if you have any questions or any podcast topics that you’d like to see on video or listen to the audio podcast, always email me at podcast@madbarn.com. Check us out on social media, and please hit that like and subscribe button — I know you hear that on every YouTube video, but that helps us grow. And when we see more people subscribing to this, making nice comments, it just tells us, okay, we need to keep producing this content for you. So thank you so much for listening, and take care.