Transcript:

[0:00]

Before we get started today, I have a quick ask of you. A podcast’s growth mainly comes from word of mouth — your recommendations to others is the best way to grow any podcast.

[0:07]

And here’s my ask today: if you’re enjoying any of these episodes, or if there’s any story that touched you, if you wouldn’t mind, can you share it with a friend or on your social media feeds?

[0:26]

Like today, I’m going to tell a story of my favorite mare, Tari — how she conceived and eventually gave birth to her first foal, Prairie Rose — and I have a feeling you’re going to love it. And if T’s story resonates with you today, if you don’t mind just sharing it with somebody, it will mean the world to me.

[0:47]

Thank you. [Music]

[0:54]

Imagine a pasture in Central Texas in the winter. In December, it’s a balmy 40°, slight chill on the wind coming from the north, and my mare Tari is standing there grazing on what little pasture there is, and walking over to the big round bale and getting some mouthfuls of hay.

[1:21]

What Tari doesn’t know is that when she was born, in her ovaries were all the eggs — or what we call ova or oocytes — that she will ever need in her life to produce offspring. Each of her ovaries has upwards of 700,000 oocytes, but she will only ever need to ovulate around 100 in her entire life.

[1:45]

But you know what? Tari doesn’t care right now. Her body doesn’t care right now — it’s winter, and reproduction is the last thing on her mind. It’s long nights, she’s taking short bouts of sleep, she’s focused on foraging, eating hay to feed all those microbes in her hindgut to keep her warm.

[2:05]

And what she doesn’t know is that in her brain, her pineal gland, during the hours of darkness, is secreting this hormone called melatonin — and it’s suppressing any thought or hormone associated with reproduction. She’s just focused on staying warm and maintaining her body condition the best she can.

[2:31]

But what Tari doesn’t know is that just in a few short months in the spring, all of that is going to change.

[2:43]

Secretariat being led. He is the horse, and the horse is the best thing in the world, isn’t it? I’ve always loved them, really, since I was a little girl.

[2:55]

Everybody’s in line… and they’re off! Secretariat away very well, has good position. The love — I never thought owning a horse could mean so much to me. Secretariat now taking the lead. The madness — what kind of a horse is that? I’ve never seen a horse like that before. Tightening now… he is moving like a tremendous machine. Their story — Mustangs were more involved in the early development of this breed than I thought they were. Secretariat has opened a 20-length lead… he is going to be the Triple Crown winner.

[3:35]

[Music] Welcome to *Into the About Horses*. Hello, I’m Dr. Chris Mortensen — I’m an equine scientist, reproductive expert, researcher, educator, and enthusiast.

[3:50]

And today we’re going to tell the story — the life of a mare — over the course of a year. Specifically, I’m going to tell the story of Tari through her eyes, as she will end up getting pregnant with her first foal, a filly named Prairie Rose.

[4:08]

And we’re going to talk about what makes Tari and other mares so special, what makes them tick, insights into reproduction, why they behave the way they do. And I’d also like you to stay tuned, because there is some critical information for any horse owner that works with mares. There are certain feeds or hormone supplements that we give horses that can be hazardous to your health — especially for women — so stay tuned for that information.

[4:40]

And just a warning — we’ll be using some reproductive anatomical terms in this podcast; I just want you to be aware of that. The mare — female horses — are incredible athletes. I’ve told the story of Zenyatta, and have yet to tell the story of Ruffian — probably the top female Thoroughbred racehorse ever to exist.

[5:05]

And then you have top competitors today like HH Azur — she’s a Belgian Warmblood, one of the top show jumping horses in the world — or Dalera, one of the top dressage mares in the world. And then don’t forget the mothers — the ones producing champion after champion. One of the top producing mares in the world is Derly Chin de Muze, a Belgian Warmblood who has produced some incredible horses.

[5:30]

Being a mother is probably one of their most important jobs, and that is the basis for what we’re going to talk a little bit about today.

[5:41]

Now, anybody listening understands there’s differences in physiology between male and female horses. Males — you have your stallions, intact — they have their testicles. Geldings — they’re castrated, testicles removed — which are producing the testosterone that makes stallions a little bit more aggressive. That’s why we geld them — to take away that testosterone.

[6:04]

But really today, the story is about the mare. How does their physiology impact our ability to manage them? Because one thing we’re going to talk about today is — horses are seasonal breeders, and I’m going to explain that in more detail. But this definitely has dramatic impacts on our ability to ride and compete with mares in certain parts of the year.

[6:28]

Mares experience what we call estrus — or “heat” — a heat cycle. And they can be a little bit difficult to manage during those few days. They can be very distracted going to a horse show — competing at show jumping, eventing, dressage, barrel racing — when a mare’s in heat, they may not mentally be ready because their physiology is dictating something else to them that they can’t control.

[7:01]

So that leads into things like using artificial hormones to suppress them during those estrus periods. We’re going to talk about all this today.

[7:19]

Horse reproduction — going back to my own career and getting my bachelor’s degree in pre-veterinary medicine — I loved everything there was about horses: horseback riding, training, nutrition, physiology. That all changed when I started graduate school and was able to work in the breeding shed. Right then and there, I was captured — and I knew immediately what direction I wanted to go in my life, and that was to become an equine reproductive physiologist.

[7:53]

That has led me in so many wonderful directions in my career — I ended up working with elephants and white rhinos — but going back to that love of horses, that’s where it all began, and the fascination with the creation of life has captured me from the very beginning.

[8:20]

Think about this — I talked about Tari. When she was born, each of her ovaries held anywhere from 500,000 to a million oocytes — those are the estimates — and she’s only going to ovulate 100-ish plus of those eggs. The oocyte is the largest cell produced by the body, regardless of species of mammal. Horses, humans, chimpanzees, elephants — the oocyte is the largest cell made: the female egg.

[9:00]

Then we combine that with the smallest cell in the body, produced by the male — the sperm cell. So you have the largest cell in the body and the smallest cell in the body coming together for the miracle of the creation of life. It’s a miracle — we know the physiology and everything behind it, but it’s still… the process, even the genetic process that I studied, is fascinating. But it’s still, to me, a miracle that it happens, and it’s… biology just blows me away the more I study it.

[9:39]

In horses, after that process, in just 11 months, you have new life. And I have foaled out hundreds of mares in my career, and still, every single time that foal is born and hits the ground, it’s jaw-dropping. It’s amazing. It’s one of the most exciting experiences that I’ve been able to witness.

[10:03]

And then that foal — and we’re going to talk about this in a follow-on podcast — how that foal gets up and going so quickly just still blows me away to this day. That entire process captured me as a young graduate student enough that I’ve gone on to publish scientific papers and study this in greater detail. It is that much of a fascinating topic — you definitely want to learn more once you start going down this road.

[10:29]

Now, to start all of this off from the horse’s perspective — even other animals’ perspective — if I was going to ask you: when do you think most animals out in the wild — and we can stick with herbivores: deer, horses in the wild, wild cattle, goats, even squirrels — when do they want to have their babies? When is the best time of year for them to give birth?

[11:04]

Winter most likely is out — unless you’re a bear hibernating, having babies, and then emerging later when the baby’s a little bit more mature. But for most animals? Winter — no way. Especially a herbivore like a horse.

[11:14]

The fall? No, that’s not optimal either — because the young would have trouble during winter. The grass is not as green or as lush, especially out in the wild. So then — spring. Spring would be the most obvious answer, right?

[11:36]

Think about it — in the spring, the bees are buzzing, especially the flies around the horse barn, the grass is greener, birds are chirping everywhere. They’re all having their babies. Most species are going to have their babies in the spring, because that’s when life is emerging from winter.

[12:01]

And so, for a herbivore like a horse, spring’s the best time to have a foal. And because of that, they have evolved over the last 50-plus million years to get pregnant, carry a baby for 11 months, and give birth when there’s lush forage — because that mare needs to produce milk to feed that baby. It’s a nutritionally demanding cycle for the mare, and you want to ensure she has optimum nutrition, which is in the spring out in the wild.

[12:41]

So if we take Tari — imagine her back in the winter, grazing on more hay than anything, but nibbling a little bit of grass, staying warm, long nights — and physiologically what is going on is, during those hours of darkness, the pineal gland (this is in us too) secretes melatonin. Now, if you don’t know what melatonin is, it’s one of those things that makes us sleepy; it makes us tired. From a human’s perspective, it’s secreted during hours of darkness — it’s one of the things that helps us fall asleep.

[13:21]

Well, in a reproductive sense in the horse, melatonin suppresses reproduction. It’s suppressing the reproductive hormones, so everything is shut down. Mares are not cycling, they don’t have an estrus cycle. Stallions — their libidos are down, they’re not as interested in breeding mares — and it’s just a quiet time in the breeding shed. For anybody that’s been around horses and it’s the winter, we’re preparing for foaling season or getting ready for breeding season.

[13:52]

Now, from Tari’s perspective — as the days get longer, more sunlight — that melatonin starts to lessen, so less and less of it during the nighttime hours. Her brain, reproductively, starts to wake up from its winter slumber, you could always call it like that. And there is a hormone called GnRH — which is gonadotropin-releasing hormone — that starts to pulse just a little bit. Pulse… pulse… pulse… and really it’s over hours, not seconds, but it starts to pulse a little bit.

[14:42]

And then that carries down — a very short distance — to her pituitary gland, which is near this brain control center. And that GnRH triggers the pituitary gland to release FSH, and that pulses — pulse… pulse… pulse — and that’s taken up by Tari’s circulatory system.

[15:03]

So here is Tari, grazing on the grass. Spring — things are getting a little bit greener, still eating a lot more hay, but she’s out there, the days are warming up — 50, 60 degrees Fahrenheit, 12 to 15 Celsius — it’s getting warmer, longer days. This hormone, FSH, is very powerful, but it’s got to make an incredible journey on its own. Because in the brain, FSH does really nothing — it’s got to go all the way down to her ovary.

[15:45]

So, a straight-line distance from the pituitary gland to a mare’s ovary is like six to eight feet — let’s say Tari at six feet — but the circulatory system is a series of twists and junctions, and it’s not a straight line. If you laid out the human circulatory system from end to end — so every blood vessel — it would stretch 60,000 miles. I don’t know how many times that is around the Earth. So this hormone, in horses that are three to four times as big, has a far way to go — this little tiny molecule — but it’s so powerful because when it gets to Tari’s ovary, it starts to trigger some changes, and she starts to develop what we call follicles.

[16:26]

Now, let’s say Tari — let’s just make it an even number for discussion purposes — has a million oocytes in her ovaries. Most of them are held in diapause — they’ll never grow, they’ll be there until Tari dies. But a few — a handful, ten — are triggered, and they start to grow. And the cells around this egg, or oocyte, that Tari has start to double, and then those cells double, and it starts to grow into this follicle.

[17:00]

Well, what that does — and what the follicle starts to produce — is the hormone estrogen. Most everybody listening knows what estrogen is; that’s the primary hormone for women that helps dictate their cycle. Same thing for horses. So estrogen starts to be produced by these follicles, which is then picked up by the blood and carries all the way — those thousands of miles or kilometers — back to Tari’s brain.

[17:34]

So she’s out there grazing or eating some hay, and she’s like, “Huh… I haven’t felt this in a while,” and she’s tingling a little bit. “Nah… no, no, no, no, just not yet… not yet.” And this is the transition period. This is a period in mares, in early spring or late winter (depending on where you live in the world), where mares have erratic estrus cycles. So one day they seem like they’re in heat, the next day they’re completely out of heat — they have no interest, they’re back to doing what they do day-to-day. Days in heat — “Wow, you know, find me a stallion” — and it’s very erratic.

[18:19]

And it’s not a good time — that’s not when you want to breed them, when they have erratic cycles, because they won’t be able to conceive and maintain a pregnancy. So this spring transition is due to them being seasonal breeders.

[18:26]

Now, I said horses’ gestation — the length of their pregnancy — is 11 months, 330 days on average. Some variance in there — some mares give birth at 320 days, some take longer, up to 380 days. On average, you’re looking at 330 to 340. I’ve only worked with one mare that went 12 months — 366, 367 days — it was an abnormal one. I’ve never seen this before, and that’s dealing with hundreds of mares. But they can go longer — they can — it’s very rare.

[19:05]

Now, mares giving birth in the spring — it’s because they transition from pregnancy to lactation. And whenever I talk nutrition or teach nutrition, lactation is one of the most demanding times in any horse’s life. When mares are lactating, it’s up there with intense exercise — a lot of nutritional demands being placed on the mare. And so that’s why they want their babies in spring, so they can support that lactation.

[19:39]

Now, as that melatonin gets less and less — as the days get longer and longer — so you have less suppression of GnRH in that brain center, generally in the Northern Hemisphere the breeding season for horses starts about mid-April and can run to mid-September. Hours of daylight are going to dictate this. Now, in the Southern Hemisphere that is reversed — when it’s spring/summer in the Northern Hemisphere, it’s fall or autumn and winter in the Southern Hemisphere — but we’ll stick to the Northern Hemisphere, it’s a lot easier to explain this.

[20:21]

Now, it may be April to September, but if I say go up to Alaska or Northern Canada, that breeding season is going to be a lot shorter — their days get shorter sooner. So South Florida is going to have a longer breeding season than, say, the northern United States or up into Canada.

[20:42]

Now, we left Tari in transition, in her first full estrus cycle. That FSH is feeding down from the pituitary to her ovaries, the estrogen is feeding back up to her brain, and then also impacting her reproductive system. And it starts to also dictate this other hormone called LH — or luteinizing hormone — and that’s what causes her to ovulate, or release an egg from her ovary.

[21:19]

So you have this feedback mechanism — once she ovulates, then it transitions to seeing if she’s pregnant, which we’ll talk about in a minute. But it builds up an intensity — you have an FSH… pulse… pulse… then when you get an LH… LH, LH, LH, LH, LH, LH… ovulation. So it builds up in intensity. And the reason I’m saying this, and the reason I’m talking about this, is because that buildup in intensity means she’s releasing more estrogens, and that impacts her behavior.

[21:59]

It impacts her ability — and the best way to summarize this — her ability to focus. Her ability to go into an arena and compete, or even get in a trailer. Because that estrogen peak is so intense for her that it really makes it difficult for her to focus on other things, because her biology is telling her, “I don’t want to go jump something… I need to get pregnant.” Her body’s telling her, her biological clock is telling her, and it can make mares cranky.

[22:38]

But the good news is, the estrus cycle in horses is 21 days. For 15 of those days, there’s really not a lot of estrogen — progesterone’s high, things are quiet, she’s focused. It’s really for those five or six days, when estrogen starts to peak, hits a plateau, and then quickly dissipates within a couple days — it’s those five or six days that she’s easily distracted or tough to handle. And I know most of you probably already know this working with mares — just giving you the physiology.

[23:22]

Now, her estrus behavior is absolutely normal for her. And it is normal for her not to eat as much — she won’t be as hungry. She’s very sensitive to touch, so even any training cues, or when you try to saddle her, she might pin her ears back where normally she doesn’t. Her face might grimace — we were talking about that grimace scale — she just seems a little irritable sometimes. Or, if she sees a stallion or is anywhere near maybe even a gelding, she may do some of this estrus behavior — where she’s neighing or whinnying more, she’ll raise her tail, and what we say — her vulva will “wink” — and she’ll urinate a little bit. She’s really interested in stallions. That’s her physiology dictating it.

[24:12]

And so I think we really need to be understanding of that, because I think some people don’t understand — “Why is my mare acting so weird?” — and you just have to realize that’s part of it.

[24:24]

Now, those other 15 days I talked about — you have an ovulation, and now it’s a time of quiet. Her reproductive system is quiet, and there’s nothing going on because this is a time where, if she was bred, you need time for pregnancy to be recognized. So for that two weeks — between 14, 15 days between estrogen peaks — if she’s pregnant, she won’t recycle. And progesterone — for many women listening, you understand — progesterone is a critical pregnancy-maintenance hormone. If there is no pregnancy recognition, then she’ll recycle. Her ovaries will become more active again, that GnRH starts pulsing, FSH starts pulsing, starts producing estrogen, that LH surge to ovulation — and she does this over and over and over until she’s pregnant, or the end of the breeding season.

[25:31]

Then melatonin will transition her out — so again, an erratic cycle going into fall/winter — and she’ll transition out when melatonin gets to a level that it suppresses GnRH enough that she doesn’t cycle until the following year.

[25:44]

Now, going back to that estrus behavior — this is probably the most critical part of the podcast. If you take away anything — female or even males — this is it. Big warning. Everybody needs to know this, and every time I taught reproduction — doesn’t matter the species — I would talk about using things like Regu-Mate, a synthetic hormone, or what we call it — altrenogest — that suppresses estrus behavior in mares. Regu-Mate is the most commonly available around the world; that is orally dosed or orally fed to horses.

[26:27]

Now, why is it so critical you need to know this? Because you don’t ever want to get this on your skin — especially for women. Even men have to be careful with it because it can have some impacts, but for women, really, the worst is — it can cause early menopause in very young women. It’s also reported that women who have gotten it on their skin have severe menstrual cramping. In fact, last year the FDA in the United States worked with Merck Animal Health to update the labeling of these products because there have been reports of so many adverse effects on women.

[27:15]

So this is a drug — it’s like a progesterone — and the skin, our skin, is an organ and it absorbs chemicals relatively easily. So if you get it on your skin, you will absorb it into your bloodstream. This is why you need to be very, very, very careful. And men — for your sisters, your daughters, your partners, any of your female friends — if they’re using Regu-Mate, be very, very cautious. I always tell everybody: use gloves anytime you get near that product. It’s just not worth the risks.

[27:55]

The FDA did talk about adverse effects reported in 137 different people — 115 were women, 22 were men. Eighteen of these women were just teenage girls as young as 14, and they had reports of abnormal or absent menstrual cycles. In men — decreased libido. Also, physical effects like fevers, headaches, vomiting, diarrhea, all sorts of things. And then the FDA recognizes it’s probably underreported because they figure exposure is a lot more than what they know. And it’s not just when they administer — because if you orally dose a horse, say you put it in your feed bucket, and then later you’re cleaning your feed bucket without even thinking about it, and there’s some leftover Regu-Mate residue — that gets on your skin.

[28:47]

So anytime dealing with this — be very, very, very careful. And I’ve been passionate about this for 20 years, when I learned of a friend of a friend who had early menopause in her 20s because she was feeding Regu-Mate and didn’t realize getting it on her skin would cause her so many issues.

[29:07]

So — why we use it though, why is it used? Because we do compete with mares year-round. Not every mare is a broodmare — most mares are out there competing or are riding horses. And if you feed them Regu-Mate during this estrus period, when that estrogen is peaking, it will suppress that behavior. A lot of people will use Regu-Mate when they plan on going to shows — they can feed it up to 15 days. This isn’t something you want to give long-term over the breeding season, but for example, if you had a show on a weekend, you could start feeding it earlier in the week if you track her cycle, knowing that she’s probably going to be in estrus and you want her to focus on the horse show.

[30:01]

So people do use that. It’s also a great product that we use in the breeding shed to help mares through transition. If we’re doing embryo transfer and we need to sync mares, we use Regu-Mate. It’s got a lot of great uses — that’s why it’s still used a lot today.

[30:17]

But again — use it cautiously. Back to Tari: late May, Tari’s cycling normally, her reproductive system — which I’m going to explain here in a second — is in perfect health. And just to explain how the mare’s reproductive system differs from, say, other species: starting on the outside, the vulva, going into the vagina. The vagina of a mare is 6 to 8 inches, or up to 20 centimeters long, leading up to the cervix.

[30:50]

Now, the cervix is interesting in horses. It’s different than other livestock species — it is a muscular-type cervix, and it makes artificially inseminating horses really, really easy. Something that I used to teach my undergraduates all the time — teach them to go in and artificially inseminate mares when that estrogen is high. So with Tari, her cervix is going to be open and loose. When you go in there to AI, you can feel it and realize you can easily pass a pipette through there. When progesterone is high — when everything’s quiet — that cervix is shut tight. And when she’s pregnant, that cervix is shut down for business — it’s shut super, super tight to protect that fetus.

[31:40]

But very interesting — the mare, how it differs from other species where, like cattle, they have cartilaginous rings. It’s trickier to artificially inseminate a cow versus a horse. So, going into the uterine body — the horse has the main uterine body, which is 10 inches or 25 centimeters long. Then there are two uterine horns — each horn is just as long as the uterine body, 10 inches or 25 centimeters. Now, horses can’t carry twins — ultra, ultra rare. There’s not enough room in her uterus to safely carry twins, so it’s something we don’t like to see when we do ultrasound scans. Very rarely a mare can carry them to term, but those uterine horns are probably remnants from a time when they might have been litter-bearing species — pigs, cats, dogs, other species that have lots of offspring have really long uterine horns. The horse — there’s two, and they’re short.

[32:48]

That leads up to the oviduct — two oviducts, because two ovaries. Ovulation in horses is actually the longest in any known domestic species — again, 10 inches or 25 centimeters long. So they’re all pretty similar in length. And this is where the site of fertilization happens — where the sperm cell has to swim all the way up there to meet the egg to make the miracle of life happen.

[33:13]

So, back to Tari: diestrus — progesterone high — not interested in the stallion. Then estrus starts — cervix is opening up, starting to demonstrate interest in stallions, what we call behavioral estrus. And in modern breeding, a lot of times we use ultrasound — so we will go in and scan her and look at her ovaries for activity, and we measure her follicles. And when she has a follicle 35 millimeters or larger, generally that’s when we want to breed her. Her largest follicles are going to grow about 3 millimeters a day, and they ovulate for, like, a mare like Tari, at 40 to 43 millimeters in size generally.

[34:06]

So once she hits that 35, 36 millimeter-size follicle, we know she’s going to ovulate probably within 24 to 48 hours, so we need to breed her if we want her to have a baby. Now again — largest cell in the body coming out of the ovary, smallest cell in the body, the sperm cell, has to make one of the most incredible journeys I’ve ever learned or seen in nature. Because just the distance from the cervix of the mare up to the oviduct is roughly 24 inches, or 60 centimeters — and you’re talking this microscopic cell has to swim that journey the whole time the mare is trying to kill it.

[34:50]

And to be honest, the mare does not want any foreign cells in her body — her immune system is fighting off everything all the time. And that little sperm cell has to make that journey — but they do it, and they do it within four hours after breeding. We know, doing the research, that there are viable sperm cells up in the oviduct within four hours, and they can last upwards of five days in the oviduct. Horse breeding — it’s a timing thing. Once the egg’s ovulated, with the mare it has about an eight-hour window where it can be fertilized. So you need to make sure the sperm cells are up there when she does ovulate, so when that oocyte comes down you have a greater chance of pregnancy. Timing’s everything in horse breeding.

[35:40]

But back to Tari — when we first bred her, back in the day — this is like 20-ish years ago in the breeding shed — we used artificial insemination, which we can use in Quarter Horses. And we physically deposit the stallion’s sperm cells into her uterus, so we bypass the cervix and go right at the base of the uterine body. We always recommend 500 million motile sperm cells, and a stallion can produce anywhere from 4 billion — I’ve seen upwards of 50 billion viable sperm cells. Generally, 500 million is the breeding dose.

[36:12]

And then we let Tari go back to her pasture — and she’s in heat, and she’s probably neighing at the stallion as she’s gone by. We teased her earlier to make sure she was in heat, and all the things that we do. And she’s going to eat a little bit. But after ovulation, her ovaries start producing progesterone, things quiet down, she’s not interested in stallions, and now it’s a waiting game.

[36:39]

But little did she know — overnight she ovulated, the stallion’s sperm cell fused with her oocyte, and her daughter — who will go on to be known as Prairie Rose — was just conceived. The miracle of life has just begun. And Prairie Rose is just a single-celled embryo right now, but she’s up in her mom Tari’s oviduct. And within 24 hours, she’s in two cells, then four cells, then 16 — each cell’s replicating — 32, 64, thousands of cells, eventually millions, billions, even trillions of cells once they’re adults.

[37:20]

But you know what Tari’s doing right now? What’s she doing? Progesterone high — she’s just eating, she’s relaxing, enjoying the sun on her dun-colored back. That’s what she does — she just eats. And five days later, after conception, Prairie Rose is doing all the work right now — mom’s just quiet, which is good. We’re not exercising her, we’re not riding her — that was actually my PhD work, showing that exercise was detrimental to reproduction (that’s another talk for another day).

[37:54]

Prairie Rose is now an early embryo — day five. She’s a group of cells in a sphere, so we call it a morula, or early blastocyst. And she comes down finally into Tari’s uterus. And this is where a lot of magic happens — in horses, and in any pregnancy really — but in horses, the embryo starts its own journey. So it starts to migrate — down the uterine horn into Tari’s uterine body, back up the other horn, down, back into the uterine body, and up the other horn again. And they do the circuit in about two hours.

[38:34]

All the while, the embryo is signaling, “Mom, I’m here.” Tari, “I’m here.” Prairie Rose is saying, “Tari, please, Mom, don’t recycle, you’re pregnant.” Tari’s just eating, “Okay, okay…” But that pregnancy recognition is critical so she doesn’t recycle, and that cervix stays closed.

[38:54]

Now, horses are a lot different than humans and other species — the embryo does not burrow into the uterine wall. By about day 15, day 16, this embryo is now a blastocyst — it’s big — it gets stuck at that uterine horn and uterine body position. It’s so big now that it just gets stuck, and it can’t migrate anymore. And it gets to a point at the base of one horn — we call it fixation — and now that’s where the embryo is going to start growing.

[39:34]

Now, I’m going to let you into a little secret — it’s one of the most fascinating facts about reproduction that still blows me away today. And for horses, this happens around between day 30 and day 40 of pregnancy. With us, it happens earlier on, and it’s known as a pregnancy paradox.

[39:50]

To explain this — our immune systems are designed to fight off any foreign cells, foreign DNA. That’s what keeps us healthy, that’s what keeps us going. And so, what that means is — a pregnancy — Prairie Rose is half Tari, yes, but she’s also half dad, half stallion. So the DNA that’s in Prairie Rose is foreign to Tari. My DNA was foreign to my own mother.

[40:22]

And it’s a paradox because the immune system should recognize that, and the immune system of the uterus is very robust — it should attack and kill off the baby. None of us should really be here — that’s why it’s called a paradox. We can’t fully explain it. We do know there’s some gene signaling now, and as we get more advanced in biomedical sciences, we’re able to explain this more. But it is one of the most fascinating facts, when I talk about reproduction, that mom’s immune system should have killed us off — but they don’t.

[40:55]

And so Prairie Rose, during this period, is communicating to Tari to say, “Hey, do you mind… just let me live for a little bit.” And Tari’s immune system’s like, “Hmmm… okay, all right, okay, yeah sure,” and it tolerates the pregnancy. And that’s why we’re here today. So it’s just a fascinating look at reproduction.

[41:20]

And as time goes on, Prairie Rose is still developing. By day 24, she has a heartbeat. By day 40, she’s like a tiny, tiny foal that measures maybe 3 inches long, or 8 centimeters long. Tari, at this point, physically, mentally — normal day-to-day. Again, you can exercise light to moderate, but any moderate to heavy exercise, I would tell you — don’t, please. My research showed that it’s detrimental in early pregnancy.

[41:56]

Progesterone is the dominating hormone. Then we get these pregnanes and other things that come into it. But for most of her pregnancy, those first two trimesters — or roughly eight, nine months — not much is going to change for Tari. Yeah, she’s going to start filling out a little bit. The fetus is still very, very small — up to day 120 in pregnancy, it’s maybe four pounds or two kilograms, roughly. You get some growth in that second trimester — that foal’s getting up to, say, 33 pounds, 15 kilograms, by day 240.

[42:29]

The last trimester is where you see this massive, dramatic growth in the foal. They can get up to 120 pounds, 54 kilograms, at term. So from 33 to 120 — you can see that curve goes way up. And so this is where Tari’s nutrition is going to shift — she’s going to need a little bit more support. Not dramatically yet, but some support to help support Prairie Rose growing. Then when she lactates — that’s when you’re going to see the demand.

[43:02]

Now, for Tari — April the following year, 333 days since the day she conceived Prairie Rose — she’s felt a little bit different the last few days. Today, she really feels it. She looks around the pasture, her pasture mates — she’s wondering where she can go and be by herself a little bit, lay down, get away from the others. Her instincts, her brain’s telling her, “I need to go, I need to go somewhere else, I need to be somewhere away from these other mares.”

[43:39]

She can feel the foal kicking in her a little bit, the jostling, and she’s wondering — “Is it today? Hmm… maybe we’ll wait until it gets dark.” Yeah, Tari’s thinking, “It’s today… but I’m going to wait till the sun goes down.”

[43:59]

And then, just a few hours later, in the hours of darkness — Prairie Rose is welcomed to the world, and she takes her first… [Music]… breath.

[44:13]

I love everything about horses. I just — I go back, and I have all these memories, great memories, of learning things for the first time. I think maybe that’s why I love doing the podcast too — it’s just that information, things I never knew before. And when I get new bits of information, like the pregnancy paradox, or what makes horses so unique and special reproductively, or anything with them — it just… I get so giddy, and I hope you do too.

[44:47]

And again, it’s always important to me that you know how much I care that you’re listening — and especially listening to this point, that means you consumed the episode and you’re still listening to my voice, so thank you.

[45:01]

And like I asked at the beginning — if you don’t mind sharing this podcast, or your favorite podcast, with one person, two people, thousands if you have those followers — millions if you have those followers — on social media, it just… it will warm my heart. I mean, telling these stories about horses — just this morning, on a meeting, telling the team at Mad Barn — you cannot convince me that horses aren’t the most important animal companion for us. You can’t. You can’t. So thank you for that.

[45:27]

If you haven’t given a five-star review — I know that kind of glosses over again in your head — but if you haven’t, if you don’t mind just… okay, yeah, Chris keeps asking… at least you won’t feel guilty — just open up the app, five stars on Spotify, few words, I’d appreciate that too. Or iTunes.

[45:45]

Again, just a reminder — anything reproductively too, articles on madbarn.com under the Learn tab. And then just catch us in social media, in that space — I’m in there: TikTok, YouTube, Facebook, Instagram. And then any comments, any topics — give me some topics: podcast@madbarn.com — I appreciate any recommendations you may have on a topic that you want to learn more about.

[46:11]

But again — thank you for listening. Just means the world to me. And stay tuned — another great episode coming your way. Take care.