Alright, welcome to the Estrous cycle lecture, and

we're actually laughing here in studio, I have

to be careful because I could sit here and spend an hour just talking about this.

Because we do so much management with it.

And how we manipulate the cycle and, and track the cycle.

And it's so critical in making breeding decisions.

So if, if your unclear please ask in the discussion boards or

seek out external information, because This is a, a lot to, to handle

in a, in a short lecture and really is what I base a

lot of my, my classes I teach with my students here at Florida.

Now to start this lecture off, the, the first

thing is, what's the difference between estrous and estress?

All right, so they sound the same right?

So you're looking at you know, you're going to, you'll see it

Is estrus without an o, and then estrous with an o.

And basically, I just wanted to, to start with the verbiage.

So, estrus without the o is a noun.

So, it's actually stating her behavior.

So, the mare or the jenny is displaying estrus.

The estrous cycle, with the o, here, it's actually

an adjective and that's actually descriptive of the cycle.

So that's kind of what the difference is and

I always like to start that lecture out with that.

Now what you're really going to focus on with, with the horses and to an

extent the donkeys is, they're seasonal breeders and

that's going to dictate on the day night cycle.

And we're going to jump in to why that is and And

I actually made this map a while back for my students.

And you can kind of see, you know, the

equatorial region where we have, you know, most of

the day length is the same thru out the

year, and then depending on the tilt of the Earth.

Which I highly recommend the astronomy courses thru Corsair.

They're actually really cool and I have taken 3.

With them, but the tilt of the Earth

dictates you know, the season all that fun stuff.

So in the northern hemisphere, the natural breeding season for horses is March

through September and that might differ a little bit ag, again as you

get closer to the equator that may be longer for our folks up

in Alaska, hello, you know, or up in Greenland, its going to be shorter.

you know, and then in the Southern

Hemisphere, it's the, almost the exact opposite.

So you're looking at the, the natural breeding season would be

October and May and for any horses that are on Antarctica,

which I don't think there are, but if there are, their

season is going to be really short and in the Southern Hemisphere.

Now

So, horses are called seasonal polyesters as you're going to see and I threw

some terms in there so it's like

clarity and different species have different cycles.

So polyestrous is like females human.

Females and then you can also see cattle, swine, rodents.

They actually have uniform cycles throughout the year, so

they can get pregnant almost any time of the year.

Now monoestrous, these are animals that have one

cycle a year, like the bears, you know, so

I had, I had to have an excuse to throw up some cubs and, and mama grizzly.

So, pretty cool picture there.

So they, they have one cycle per year, and they

breed and, and hopefully get pregnant and can carry on.

And then the equids are seasonal polyestrous, so

they get a bunch of cycles during the season,

and then they shut down and they're out of season for the other part of the year.

Now sheep, it's interesting are actually opposite of

horses, where they breed in the winter months.

Where horses are more spring summer months.

Now, why is this?

What's the physiology?

What's really this, this hormone called melatonin and, and if you don't know it

or not, but melatonin is the one [SOUND] that oh makes us tired at night.

Man I, that felt good to yawn.

So melatonin's what, you know, when all the lights are off.

You're laying in bed and you eventually get sleepy and fall asleep.

It's because melatonins going up, pineal gland

that you're not getting the, the light.

So that's important in our circadian rhythm, and then the, in this, you know

graph here, you can see you know,

late at night, that's when melatonin's peaking, okay?

So melatonin Actually in horses suppresses the reproductive axis,

so if you just looked at this and again this is very complex and you know beyond

the scope of this class but is something that, you know, in future

classes if you take anything in reproduction you would have to know this.

But this is the hypothalamic, so hypothalamic pituitary.

Ovarian access.

And what melatonin does, you can see it starts with

the pineal gland, is in horses, it suppresses the hormone GNRH.

So suppresses that axis.

So it's going to shut them down reproductively.

And this effects males to.

So the stallion and jacks during the winter months.

You can still probably collect em, but

they're, they're semen parameters, their sperm cell characteristics

are probably going to be a little bit lower

and different than the peak of the season.

So and their libido, they're not going to have

much interest in, in breeding during those off months.

So that's really the physiology behind it.

What's causing that.

Now without getting too much into it you know the evolution of the

horse and why this is is you know they have this really long gestation

length 340 days in horses, 360 days in donkeys or if it's a mule

gestating you know within a mare That can go out to 12 months, too.

So, they take a little bit longer.

So, they, they, they have this annual breeding cycle.

You know, 11 months, get pregnant right away

and then have another baby a year from now.

So very very important in you know, our breeding decisions.

Now what do we, what do we do?

Well good old, you know, us humans breed registries.

They actually have gone and mandated an annual birth

date for horses in their, in their breed registry.

So So, it a, it behooves you to check your, your breed registry

rules and regulations and, and some of em are a little bit different.

They're, they're actually later in the year, but typically

and, and I'll use the jockey club as an example.

Their annual birth date for, for horses in the northern hemisphere is January 1st

and then any horses in the southern

hemisphere, their birth date is August 1st, okay?

So, any horse born, say, in Florida last July Let's say he was born in July.

Even though they were six months old January 1st of this

year, physically, they were considered a yearling by the Jockey Club.

Now, that's important for age-restricted events, so

things like, you hear about the Kentucky Derby

or the Breeders Cup Race, well, not the

Breeders Cup Races, but the the Kentucky Derby

And the preakness and the belmont stakes,

those are actually for three year old thoroughbreds

so can't be two can't be four plus, you have to be a three year old.

So, horse owners have gone and tried to manipulate the breeding season.

To have horses born as close to January

1st as possible without leaking into the other year.

So, you know, there's different strategies and we will

talk about that at the end of this lecture.

Now, the estrus cycle is really the term where we call From ovulation to ovulation.

So here's an ovulation here, here's an ovulation here.

So in horses that's 21 days as you can see.

And then in donkeys it's roughly 24 days.

It can go a little bit longer then that.

So that's from.

You know we call this interovulatory period from ovulation to ovulation.

So, so 21 days between ovulations in horses.

And there's two phases there's this diestrus or luteal phase so, you know

we're going to talk about that a little bit, what's going on there.

And then you have the estrus phase of the follicular

phase, so that's where she's actually getting ready to, to ovulate.

Now the diestrus phase you've got some hormones going on your

LH and estrogen are decreasing from the previous cycle And really,

the most important hormone to, to talk about is progesterone, because

that has really critical importance to maintaining early pregnancy in the equids.

So in these images, this is a preognitory follicle.

So, in the cycle, that's about right here, if

we're looking at the one up, up to the right.

And then after ovulation this is the, the whole genesis of leading up

to a egg and you can really see it good in this one.

What we call a corpus lutetium and that's the structure

that's left in the ovary and that's what's producing progesterone.

So it's actually very, very critical and it takes about five to seven days.

to, to form on the ovary.

Now, you also do see this FSH here

and that's producing follicles in case she's not pregnant.

Really getting ready for the next cycle.

So you'll see some follicular development, but,

but they're immature follicles that haven't matured yet.

And.

Really, the importance is, during this

high period of progesterone, everything's quiet.

Shh, I always tell my students.

Really, you're trying to be as quiet as you can.

So for this early embryo that's coming down, and here's an,

here's an embryo from one of my research projects from Texas A&M.

And Doctor Caterine Hendricks [INAUDIBLE] labs where

that's a early horse blastisis and that's where

it comes down into the uterus and you

want everything quiet you want, you want everything

just you're waiting for maternal recognition of

pregnancy you want everything to be perfect for

that embryo so really under high periods of

[INAUDIBLE] that's what's going on under the cycle.

Now, let's say she isn't pregnant.

Let's say she was never bred or something went wrong, you didn't get fertilization.

And she's not pregnant.

Well, there's this hormone that comes in called prostaglandin.

And it spikes roughly around, you know, in this

graph, it's about 13, 14, some days it's 15.

So right around this period, time period, the prostaglandin comes in.

And, really destroys that corpus luteum or eliminates it.

So that gets rid of the progesterone and she's allowed to recycle

where those follicles take off again into the luteal or the follicular phase.

Now I do want to say this too, some of

the, my research I've done in my lab And others

in the world are doing is this Doppler ultra

sonography which I'm going to show you here in a minute.

Is looking at the, the pixelation of the blood flow to that

fal, or to that corpus luteum so that's what you're seeing here.

Those, that's actually blood vessels within that CL that actually

takes that progesterone and allows it to circulate in the body.

Now, during this follicular phase, you see this LH and estrogen take off.

And estrogen, you know, very, very important in, you know,

getting that uterus ready, getting that cervix ready to be bred.

And LH is actually very, very important for the LH surge.

Which leads to ovulation.

Now this is a color do-, doppler ultrasound scan of

again, that research project I mentioned i-, in our last lecture.

And you can see the pulsation around that follicular wall,

which we're evaluating with again, Dr. Lorrie Warren and Dale Kelly.

Here we're looking at dietary effects on this.

and really what we're looking at is, you know,

we want to see more blood pulsation around that follicle wall.

And that actually, we've correlated it, in my studies and other researchers have that

the more blood pulsation you have around

the dominant follicle, that equals to greater fertility.

So that [UNKNOWN] has a better chance

of fertilizing and carrying on And getting fertilized.

So I, it just, you know, part of my research I'm doing like to

introduce that, and again some of the

technology that's being utilized by veterinarians today.

And, and these Doppler ultrasounds are actually becoming much more affordable.

So your veterinarian may start carrying one of those around.

You may see that.

Now, estrogen is very important you are

not only getting the reproduction tract ready for

sperm transport and all that but also

the LH surge which actually leads to ovulation.

Where you get that follicle to rupture, release that egg into the oviducts.

For fertilization now that estrogen is going to affect her

behavior so when there's a thing we do called teasing

in breeding management, and that is where you are actually

introducing the stallion to the mares or the mare to

the stallion however your system's set up, and you're

trying to see if she's in heat, because when she's

in heat is when you want to breed her Well

when she's not in heat, she's, she, the best way

I can say it, she's angry.

He didn't buy her dinner, he didn't bring her flowers.

She want nothing to do with him.

She's going to kick him, she's going to pin her ears back.

She is not happy.

She is not interested in that stallion.

So that's the way I kind of tell it to my students.

You know, that stallion, he, he should not be anywhere near her.

She does not want to be bred, She doesn't want to be Bothered.

Get away.

Boys are ick.

Okay.

Now when that estrogen starts to increase, she was sitting there thinking.

Hm.

I know, those flowers were nice maybe.

You know, but come to me tomorrow.

And then the next day Okay, cool let's talk okay, where is my wine

and then by the third day she is like okay, let's make a foal.

So that is kind of a gradual change in receptivity to this courtship and

some the things you are going to see is she is going to posture.

She's going to raise her tail, she's going to urinate a little bit.

She does this thing called winking of the vulva when she

does that and, and that's a mare that's ready to be bred.

Estrogen's high, probably has a very large follicle/ g debris and

that's kind of how we do in breeding management to evaluate her.

Now, let's talk about just some management tips

or, or, or ways we manipulate the estrous cycle.

And one of the big ones is a light program.

And again talking about how we have manipulated

the breeding system, this is how we do it.

So let's say you want to get your horse bred in February and you live in

Minnesota in the United States, so you're in

the very northern portion- let's just say Canada.

That's easy.

Great white north.

So hey up there in Canada you want your horse to be cycling by February

well your natural breeding season's probably April,

May later in the summer or late spring.

So how do you do that.

Well if you started a light program by December

1st and you put em under the 200watt bulb

you know, you can see this is a, a, a mare with, in a lighted barn, right there.

And you start the lights before sunset, carry it

out for 16 hours and then shut it off.

And they need eight hours of darkness.

You start that December first by mid February, they should be cycling normally.

Now you need to continue that until you

get to about naturally 16 hours of daylight.

You don't want to get her to cycle And then shut the lights off.

because then she'll go right back out of season.

So, you need to maintain that light until naturally it, it.

it's almost 15, 16 hours.

Now, for our folks in the southern hemisphere.

Let's say our, our good friends down in Australia or New Zealand.

Way down there.

You're going to start your light program by July 1st and

then by September, is when your horses should be cycling.

So that's probably one of the, the major management things we, we use.

Now, I'll talk a little bit about some hormones and.

The first one I want to talk about is progesterone.

There is a commercial product here in the United States called regu-mate.

And I absolutely, this is the most important thing I

will say probably all class long in these six weeks.

If you are female, do not handle this product without gloves.

Or be very, very careful.

I always suggest to my female students to have somebody, a male.

Touch this or feed this to their animal.

If you are treating a horse with progesterone and it

could be Regu-Mate or something you mix in the feed

can be given in oil, you know you can give

it in the mouth or some people give it in injections.

Do not get this on your skin because it is absorbed by the skin.

It is very, very high doses of progesterone.

And there's anecdotal evidence that women have gone into

early menopause in their 20's by handling these products.

So be very, very, very, very careful, so hopefully I've

gotten that across to all of the women watching this lecture.

okay, but Regu-Mate's commonly used or Progesterone's commonly used.

It's very, very powerful.

Management tool and the biggest place where you

see it is it suppresses estres behavior in mares.

So if a mares in heat going to a show she's

not going to be thinking about the show so much, she's

wants to think about the boys, she's a little bit boy

crazy, so we use Progesterone to to suppress that behavior in them.

To keep their mind on the horse show and competing.

So that's where you typically see it.

We also use it when we synchronize Or some people

use it when they're trying to help them through transition.

You can feed this for a couple of weeks when they get kind of erratic in

the beginning of the breeding season to kind

of keep things calm, or some horses that

actually have trouble maintaining pregnancy, you can make,

you know, for the first four months or

five months keep them on progesterone until the

placenta takes over and they can help maintain pregnancy.

Now, another thing we use is, is Prostaglandin.

And you use this to eliminate a CL, like we

talked about earlier, where it naturally would occur in the cycle.

So, let's say she gets pregnant.

For whatever reason you don't want to keep that pregnancy, this is what we

use to, to abort mares again, in a synchronized cycle we use this.

And then, where you commonly see it a lot is short cycling.

I just quickly, basically what short cycling is,

is you're reducing the length of that estro cycle.

So let's say the normal 21 day estrous cycle

we see that spike around day 13, 14, 15.

Okay, if we give her a shot of prostaglandin earlier in the cycle.

And, you know here typically it's around

day seven, we can eliminate that corpus luteum.

So we, we, we actually eliminated that, that, that brake.

And you can see where we've gained days.

So this is a short cycle, with

the progression around, there's your normal cycle.

And so it's it's kind of a strategy to, to kind of

gain some days on, again that annual January 1st or August 1st birth-dates.

Some people might do is, is get a

mare short-cycle if you missed her or whatever reason.

Now another thing we do is, you'll typically

see is induced-ovulating mares, so, so mimicking that natural

LH surge The two products that are common

here in the United States is hCG or Deslorelin.

hCG works very, very well, You may see it here in the states called Chorion.

The problem with hCG is mares kind of develop antibodies to it.

So, if you use it more than twice per year, they

may become immune to it permanently and it won't be as effective.

If you do it, use hCG typically the rule of them is you can use it twice.

Twice per year and then keep it at that.

Deslorelin has no known developed immunity and there

are some commercial products coming on the market now.

And you want to give this one, they have a large

breedable follicle so in horses, you know, typically 35 millimeters or larger.

We'll give them a shot of this, and then within one to two days, they'll ovulate.

So it's good for timing insemination, or

if you're doing natural cover with thoroughbreds.

You know, you give this before you go to their breeding

barn, and different situations where you use this quite a bit,

So that's it, and there's a younger me, a few years ago,

ten years ago in Texas and it's hot in Texas I'll tell you.

So we're going to talk about some common breeding systems and

jump into that and, and, and some advantages and disadvantages.

So, so I'll see you then.

Estrous Cycle

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