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All right, welcome to the next lecture on pregnancy.

And, you know, we kind of left off

with the fertilization and, and that whole process.

So the, the fertilization process takes place in the oviducts,

and we kind of already talked about that a little bit.

But it, but, I mean, again, this biology is just so amazing.

This is why reproduction is just so cool to study.

That you know, it's, actually there's a lot going

on in the oviducts where they're transporting the egg,

the ovulated egg down, and then helping the sperm

cell get up in the oviducts to fertilize that oocyte.

So there's things going on.

So there is some smooth muscle there

that's contracting, that helps a little bit.

And then the cilia is part of the cellular structure

that actually helps guide the sperm cell and oocyte together.

And then there's some fluid currents in there and then the

sperm itself, obviously by whipping its tail, it's swimming in the oviducts.

Now the fertilization process takes place in the ampulla.

We've kind of already talked about that a little

bit in the mare anatomy portion, or jenny anatomy.

And this capacitated sperm is waiting.

And when we say capacitation, you may hear

this in reproduction, that the sperm cell, you

know, can actually rest for a while in

the oviducts a few days before she even ovulates.

Up to five days, some research has shown, in horses.

And then some, some chemical trigger triggers it to capacitate.

And that means it becomes hyperactive.

So, you know, the energy in the cell, or I like to

call it, its fuel tank, you know, when it's, when it's capacitated,

it's got, you know, its foot to the floor board and it

is, it is swimming as fast as it can and burning that energy.

So it has to find that oocyte relatively quickly to be able to fertilize that

so, so these specialized sperm cells are

up there, they are specialized at that point.

Now the neat thing about in horses is their fertilization rate is

about 90%, so 90% of the time the sperm cell is going to fertilize that oocyte.

But unfortunately, you know, those 90% all aren't going to result in

pregnancy that, you know, you can even see in this slide right

here I kind of, you know, included a picture of an abnormal fertilization

that during this period, I mean, it's natural for things to wrong.

I mean, here you have three pronuclei, so probably two sperm cells and one

from the oocyte, all competing, trying to

bind, and obviously that's not going to happen.

You know, so it, it will be irregular and you will not get a fertile embryo.

So, you know, early miscarriages, stuff like that, that

is all part of the natural process of reproduction.

But, you know, 90% we say that but the majority of, you

know, pregnancies or fertilization events, you know, do result in, in pregnancy.

Where you get the the female DNA or

chromosomes, meeting up with the male DNA or

chromosomes, which we call pronuclei, and then they

fuse together, and they form a single cell embryo.

Now, you know, up to this

point everything's pretty similar in most species.

You know, these, these early cells, these early blastomere cells

of the early embryo are what we call stem cells.

So, you know, some controversy in, in medicine using

embryonic stem cell, stem cells, stem cells for research.

That's what they're talking about.

And here you can actually see them doing an embryonic biopsy where they're taking

one of these blastomeres, and they can actually do genetic testing on them today.

So, you know, with the field of genetics, we can do so

much, and we've already kind of

talked about, you know, genetic diseases previously.

But we can actually do this in horses where we can go in, get

one of those single cells from an early embryo, and then do coat color genetics

on it or, or look for certain diseases that we've already talked about, and

then if that embryo is carrying the

disease you would never transfor it, transfer it.

If it isn't, then you would transfer it.

So that's, that's actually being done today around the

world, not only in humans, us, but in other species.

Now what's so cool about these totipotent cells is they

haven't been programmed yet, so any one of those cells

is eventually going to turn into the head, or the forelimbs

of the horse, or the tail, or any of that.

So this early, early process, those cells

can still be reprogrammed to become different things.

It's this really a neat part of reproduction.

Now we are going to focus a little

bit, some things that are unique about the equids.

And specifically in horses the early embryo stays

in the oviducts for six days which is,

which is a lot longer than other species,

you know sometimes twice as long as other species.

Usually early embryos come down pretty quick.

>> Well, in the horses they stay up there for six days.

So things like embryo transfer, which is becoming more and more

common across a lot of breed registries, you know, we have to

wait to try to collect an embryo day six, six and a

half, but generally day seven is typically when we collect those embryos.

So that kind of limits us to some of the things we can do with that.

But, you know, so it's up there, it comes down, and then

it's in this what we call late morula, or early blastocyst stage.

So that's what you're looking at at day seven.

You know, those are the types of embryos that you'll actually see in a petri dish.

Now in my experience, you know, those early, late

morulas, early blastocysts, you really need a microscope to see.

But going on, you know, late day seven, day eight, day nine, you

know, in some of my studies, I'll actually, you know, take that dish and

look and hold it up to the light and you can see it looks

like a little, I call it a little golf ball, but really, really tiny.

But you can still see it and go yeah, you know, we got an embryo.

And it's always a good day when you get an embryo.

Especially when you're, when you're doing research or transferring those things.

Now another unique thing about the equids is this, this embryo.

Other embryos actually hatch out and kind of, you know, lengthen along the uterine

horns or in the uterus or actually

burrows itself into the endometrium in some species.

The horse is different, or the, even in the donkey, that it forms this capsule.

So it gets this protective barrier around it and then it just gets larger.

You know, so it's like that little golf ball i talked

about, has the capsule, then it just starts getting bigger and bigger.

And it does this to, to help protect the embryo and

then also, you know, some nutrients it picks up in the

uterus because it's, it's not hooked up yet to mom through

the placenta, so it picks up nutrients as it rolls along.

Now, we know the embryo migrates in the uterus

in the equids, okay, which is pretty unique to them.

So, it can complete that circuit within about two hours.

So, it can go up both uterine horns and in the uterine body.

And we do know, you know, through

research that, that's important for pregnancy recognition.

That that embryo's moving along communicating

with Mom, hey, I'm here, don't recycle.

You know, you're pregnant.

And that's how it does that.

And actually, the, the, you know, the research study they did

is, they actually put marbles in mares' uterus, And they never recycled.

So they kind of figured out that that mechanical action

had some importance to pregnancy recognition in the horses.

And we're still doing a lot of research, a lot

of labs around the country, around the world, are still

trying to figure out, you know, how exactly that early

embryo signals to Mom that she's pregnant so she doesn't recycle.

All right, so, normal, our normal pregnancy diagnos is done

day 14, or 14 days after ovulation, so you'll breed your

horse or your donkey, wait a couple weeks, go in with

an ultrasound exam, and really you're looking for this embryonic vesicle.

So that's what this, that's what it looks like about day 13, day 14.

So, just that, that dark, spherical shape.

So that's what we're looking.

Now the em, you know, if you're really trained you can do this, you

know, a few days earlier, but generally 14 days is when we do this.

Now, right here again, we'll kind of talk about twinning.

And I know I've talked a little bit about it before.

But twinning is something we don't want in our equids.

They, the uterus is not designed to carry twins.

So with that happening, with twins if they do try to carry

it to term it's about a 10% survival rate for both twins.

So you are looking at a really, really poor survival rate.

So we always want to look for twins, and especially

in instances where we have a double ovulation, where, you know,

we've ultrasounded her, we saw two large follicles, and she double

ovulates, then we'll definitely look for twins in our ultrasound exams.

But, you see, you see twinning, you know, more the higher incidents are in

the, the warmbloods and the thoroughbreds, say,

versus your draft breeds or quarter horses.

They don't have as high an incidence.

And it's about 20% in those thoroughbreds, roughly.

So you know, two out of ten cycles are going to double ovulate.

Now, you know, unfortunately, if you do

have twins, the, the, instead of just aborting

the pregnancy and starting all over what they

try to do with the veterinarian or trained

technician is go in there, try to find the least viable embryo and then crush it,

in hopes of leaving that other embryo alone to where it can develop on its own.

Because typically they both get fixed, like in these images

from Professor Allen's paper, which you can see down here.

You know, they become fixed, and that pregnancy is doomed.

That will never, you know, happen.

And then typically if they do get a pregnancy, in each horn, let's say they

didn't fix in the same horn, you had one in, say, this horn, and one in

that horn, well typically, what happens is, pregnancy will go on for a while, but

they'll reach a point where that mom cannot

provide enough oxygen or nutrients to both fetuses.

So one ends up dying, and then it ends up poisoning and killing the other one.

So, you know, again, 90% of the twins don't carry, so that's why we do this.

It sounds a little harsh but, you know, we're really

looking for the long run because we want a baby.

Now, talking about that fixation, that happens at day 16, which we

talked a little bit with mare anatomy, but gets fixed in that horn.

So here you can see, you know,

here's that, that, that embryo right there that's,

that's stuck in that uterine horn and you can see it gets a lot bigger.

So again, we're just getting that bigger bu, ball.

Now just some unique things about horses.

We consider, you know, horses an embryo till about day 40.

And then after this, we start terming it a fetus.

And, and basically what has happened is, well we say,

we call it organogenesis, where all the organs have already formed.

So there's a little liver, and a little heart, and a little brain and, you

know, little hooves and legs, and then for the rest of pregnancy it just gets bigger.

You know, the liver gets bigger, the

stomach gets bigger, and everything just grows.

So that's when we'll term it a fetus in horses.

You can see a fetal heartbeat around day 24 of pregnancy, sometimes you see

it a little bit later, sometimes you can detect it a little bit earlier.

But that's when we start to look for a viable pregnancy.

We'll be looking for that, that heartbeat, early on.

And then what's really cool too, is around Day 60 you can sex the fetus.

So you can go in and find out if you're having a colt or

a filly or a jack or a jenny, you know, you can go in there.

And you're basically, you're looking between the

legs just like you would with us.

And you're looking for the structure called the genital tubercle.

And then if it's forward of the hind limbs like here, that would be a colt.

If it's behind, that would be a filly.

So that's, that's what they're looking at when, you know,

say, a veterinarian, or somebody that's trained can look for that.

Now another unique thing with the equids is, and, and you know, don't see this in a

lot other species is, that they get this

endometrial cup formation between day 25 and day 35.

And it's really, really important because this is

again, you know, trying to, you know, the normal

process of a pregnancy in the equids and if

anything goes wrong here, then they lose the pregnancy.

And we see most of our pregnancy losses, you know, about day 40 and before.

So, you know, if you looked at a young mare, the

research has shown, you know a mare between three and eight years

old, as soon as you detect a pregnancy on day 14, about

82%, a little less than 82% of those will carry to term.

So you'll lose about 18% of those pregnancies in those young mares.

And we see most of that happening when all of these important processes are going on.

So, before day forty.

So these cups form.

And I'm going to show you some pictures of

these, and they are important because they secrete this

hormone, we call it eCG or equine chorionic

gonadotropin, and it's really, really critical in maintaining pregnancy.

So you can see in this, this early embryo, because this is still an embryo.

It's before day forty.

And it forms these girdle cells and it's

a discontinuous ring, so you can see it here,

and then up around here, you know, that discontinuous

ring that kind of forms all the way around it.

And for those that are Star Wars fans, I'm showing my age, I always say it

looks like the Death Star, because you have

this circle around, you know, with the embryo.

And again they're, they secrete this, this

equine chorionic gonadotropin, and it acts like LH.

So if we go back to our estrous cycle, we

still remember when progesterone is high we still have FSH circulating.

So we're still having follicles develop, and that's normal for the horse.

You know, progesterone's high, that's going on.

Well what this ECG does is, it acts like a luteinizing hormone and it causes these

follicles to either ovulate or luteinize and it secretes more progesterone.

So it's really important to maintaining pregnancy.

And then this continues 'til about, you

know, mid-gestation, day 180, when the, the fetal

gonads and the placenta take over and the,

the ovaries are done, you know maintaining pregnancy.

So if you looked at all the hormones, so we're

talking this process happening here, and here you can see eCG.

So as that spikes, you can see, progesterone goes

down a little bit, and then goes way back up.

So that's what's going on during this

process is, you're getting those endometrial cups forming,

signaling to the mare, produce more progesterone, so

her ovaries respond and then she maintains pregnancy.

Now, what's not on this graph, you know, yeah

you have estrogens here, but you have these progesterones, or

what we call pregnanes that would spike there, that

pretty much take over on maintaining pregnancy for the horse.

And the dog.

So, the official placenta doesn't really

start forming until later, around day forty.

You know, so endimetrial cups form before

then and then you have the placenta forming.

So, you know, that, that early embryo still dependent, or that

early fetus, still dependent on those

nutrients being secreted by the endometrium.

Now this lasts until about day 120 and then

you can see in this image, you know, the placenta

grows up, grows up and out into both horns

and the uterine body, where it houses that young fetus.

And if you are not really aware of it, the placenta is, it's organ in its own right.

It's made up of a bunch of cells.

They need oxygen.

They need nutrients.

So, they actually get first shot at Mom's

blood that they're, they're taking in, Mom's nutrients.

And then they pass whatever's left over to the fetus, so, you know,

the placenta is, is, is, is, is a pretty dynamic organ in itself.

Pretty cool.

Pretty cool stuff.

And then, you know, as, as pregnancy

progresses, this is one we're doing right here.

So, I found this image when I was teaching at Clemson University and I'm with

one of my graduate students who's now in vet school, soon to be Dr. Jason Anton.

And we're looking at a transabdominal ultrasound.

So this is the image that we're seeing.

And you can see the different placental layers here.

And then, you can see the fetus there, so it was really cool.

We were just testing out this, this machine to see if it's something we

wanted to purchase and you can see what it would look like around day 150.

All right, and then just, you know, I thought I'd

throw this slide in here because, you know, leading up

through gestation, that fetus just gets bigger, bigger, and bigger,

and then it just hits a point where there's no room.

I mean, it's just tight in there.

It can't really move.

And it can't really eat, and it's hungry.

And then it has a little bit trouble

breathing, not as much oxygen, and becomes stressed.

And then that leads up to, to parturition, or birth.

It signals to Mom, okay, I'm outta here.

I'm ready to come out and meet the world.

So, you know, looking at that pony again, you know, where she's

huge and that, that foal inside her is ready to get out.

So, that's what, that's what kind of

triggers the, the parturition cascade, leading to

our, our next lecture which will be parturition, so as the baby's come out.

So we'll, we'll, we'll stop here and then I'll see you in the next lecture.

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Pregnancy

The Horse Course: Introduction to Basic Care and Management

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