There are over 100 million horses, donkeys and mules in the world today and owners of these animals can be found on almost every continent and in almost every society. The Horse Course will cover many unique aspects of equine ownership and touch upon the science behind many of today’s management practices.
Equine Genetic Disorders
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From the course by University of Florida
The Horse Course: Introduction to Basic Care and Management
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From the lesson
Maintaining Equine Health
The topics this week will focus on equine health. Monitoring and taking care of your animal’s health is critical to owning any equid. We will start off with the normal equine vital signs and then we will discuss administering first aid to your animals. We will then cover the different parasites and diseases that can afflict these animals. Finally, we will end the week discussing some common genetic disorders.
Meet the Instructors
Chris J. Mortensen, Ph.D.Professor
Animal Sciences
Alright, welcome back, and in this lecture we're going to talk
about some genetic disorders and just as review, you know, it,
it's [INAUDIBLE] I'm not going to make you genetic experts, but we
should You know, kind of remember and understand how chromosomes work.
So, remember, you know, we talked about the, the different chromosomes in horses.
Horses have 64.
Donkeys have 62.
You know, each set of chromosomes, so let's say in
a horse, 32 came from mom, 32 came from dad.
They came together and they formed the, the embryo that, that becomes the foal.
[SOUND] So each chromosome has as paired, and
one comes from mom, and one comes from dad.
Okay, so that'd be kind of important in, in, in understanding, especially
when you talk about these genetic disorders, and how we get them.
And how we see them in our animals.
[SOUND] So here the list of genetic disorders
that we're going to kind of cover in this lecture.
And you can see they effect, you know, particular breeds or types of
horses, so, you know, it, it behooves you to pay particular attention to
any type of breed you, you, you have, and look up at that
breed to see if there's any
particular genetic disorders associated with that breed.
And, and a lot of these came about because, you know, we
were doing specific breeding and you know, we tend to, to introduce
kind of some, you know we call it homozygosity or inbreeding
where you start to see these genetic diseases, you know, rear their ugly heads.
So the first one we going to, we going to to
cover is overo lethal white syndrome or you know
you'll see me in some of my notes do OLWS and this is wh, what I'm referring to.
Now as a reminder, there are no, albino horses, they
do not survive, you know, in utero during gestation they die.
SO there are no true albino horses, but you know, these foals
that result from this are white, they're not albino but they are white.
And we typically see this in, obviously, paint horses or stock-type horses.
But you can see this in white coat color patterns
of miniature horses, Arabians, thoroughbreds,
and then obviously Quarter Horses.
So the, be aware of that, that, that this disease can, show up.
Now, what is this?
What happens is, is causes a disease or recalled a
condition called aganglionosis, and the
digestive system can not function properly.
It, it just can't, they can not digest food at all.
So there's no way they can survive from this disease and, and, and
they usually pass, you know, or are euthanized or die within 48 to
72 hours and You know all the repra that we're going to get
into next week, nothing is worse than having a full die on you.
I hope none of you have to see that.
So that's kind of the purpose of this lecture, to, to make you aware
of out there so you make more
informed decisions, especially if you are a breeder.
So how we see this disease is two overo
horses and they both have to be carrying this disease,
for this gene mutation that is in the gene,
and the spread it or you get lethal white condition.
Now the horses that are carriers don't have any symptoms,
they're what you call hetero zygotes for this disease, meaning.
One, so let's just say for example, this just came from
mom, so that chromesomes came from mom this one came from dad.
And there heterozygous, and we're going to denote for this disease and N O, and so.
You know, they're carriers of this disease, but they don't have it,
obviously, because if they do, the double zero, that's the lethal white condition.
So there's no way they could, you know, a, a homozygous carrier can, can pass
on these genes, because they, they passed, you
know, or died, a couple days after birth.
So how do you remember heterozygosity and homozygosity?
Well I don't, [INAUDIBLE] don't put memes in my lectures but
I thought this one was just hilarious when I saw it.
You know to, to kind of in your mind
kind of understand the differences between hetero and, and homo.
So [INAUDIBLE] the zygotes when it comes to that.
So heterozygoats in this, in this funny thing was these oreo colored animals.
And you can see where, where half of those genes came
from its mom, half of those genes came from its dad.
And so its coat color was, was kit, you know, split in the middle.
So, Heterozygotes, you know, you can kind of think of, of mixing.
Where Homozygote is, you know, this white one where, you know, they, both
parents had a white coat color so that's what, what this one had, so.
So it's one of the easy way to kind of remember this.
Heterozygousity and homozygousity.
Now, just going to show you an example so we can kind
of understand the genetics of this and how this Mandillion inheritance comes about.
So, going back to anybody that's had basic genetics,
you always go to this thing called a pundit square.
And, and that's what this is.
So we're breeding one heterozygous carrier, so that's this one right here.
So, they are a carrier of this disorder.
So, remember, one of these came from its mom, one
of these came from its dad or, or vice versa.
And then this one is homozygous negative.
So, that arrow is pretty terrible.
But homozygous [LAUGH] negative, if you could see that chicken scratch there.
So, homozygous negative and so it's not a carrier
of this disease and, and so if we do
this Punnet square you can see You know what
your chances are of producing a lethal white foal.
[SOUND] Now, in this example, 50% of the offspring will be homozygous negative.
So they are not a carrier of this gene.
But 50% of the offspring have a chance of being heterozygous.
So they can actually spread the disease.
But, you have no lethal white foals.
So even though you're perpetuating this, this
disease, you're not actually or this condition.
You're not actually producing any lethal whites.
But when we turn around and breed two heterozygous carriers Okay,
what your chances are 25% will produce a lethal full.
So a 25% chance that, that full will have this lethal white condition.
Now 50%.
Will be heterozygous and then 50% or excuse
me, 25% will be, you know homozygous negative.
Not carriers of this gene.
But again this is, this is how we, why we see this.
So you can genetically test your animal to see if they're a carrier
and in the United States these tests are actually really inexpensive, it's about
twenty dollars per sample to see if your overo horse is a carrier
and if it is then you know and you can make informed breeding decisions.
Because you do not want to breed, you know,
two heterozygous carriers, or you're going to see this condition.
All right, so the next disease or condition
we'll talk about is hyperkalemic periodic paralysis, or HYPP.
Now, this one isn't lethal, so, so of all
the genetic diseases we'll cover, this is the, the
nicer of them, which, none of them are nice,
but this one is, is in particular not too bad.
And it's, it's really causing a muscle disease so what happens is, is in, in
our muscles or in any mammalian, mammalian
system, you have these sodium ion channels, okay.
And so they control.
The amount of sodium that can get in to a cell, and when
we get sodium in, in a muscle cell that actually fires or contracts.
Well, in this disease those, those ion channels are disrupted.
They don't function properly, so you actually
get leakage of sodium into the muscles.
And then, this is where those muscles involuntary contract or they twitch.
So that, that's how we see this in, in, in these animals that have it.
You know they, they, they twitch quite a
lot or really have a lot of muscle weakness.
So this was again an inbreeding situation where we were trying.
You know, earlier in the quarter horse industry, they were, they
were really trying to develop these, these really muscular, you know.
Strong-looking animals, and it develop, unfortunately, it developed this disease.
So they, they actually traced this disease to a sire called Impressive,
and he's what is called, he's known an Appendix quarter horse, or
a quarter horse with, with quite a bit of thorough bred blood
lines in them or thorough bred breeding, so those are known as [INAUDIBLE].
And you can obviously see this in paints and some
appaloosa horses, that you know, where you get some of that
quarter horse influence in there, so that's where it originated and
like I mentioned, this isn't a lethal disease, you know, [INAUDIBLE].
They, they don't die, like when they're colts, but the homozygous carrier.
These ones that have two copies of that gene, both
mom and dad had it, they spread it to their offspring.
Their definitely more effected then their hetero
zygotes offspring, where they you know the
hetero zygotes show some form of this
disease, but the homo zygotes are really effected.
So again paralysis, they can die from it
but, these horses, you know, can lead productive lives.
You just have to manage them carefully, so
it's always worthwhile to talk to a veterinarian.
When you see some of the other symptoms and, and stress, obviously, is one of
those things you want to manage because that can, can, induce an attack of this.
So genetic testing, again, is something you, you would want to do to, to see
if your animal is affected, again by the,
the American Quarter horse association or the AQHA.
You know, any decedent of the repressive line has
to be tested for this, any full that is
hetero zygote positive, meaning they have two copies of
this gene, they cannot be registered with the AQHA.
So again, consult with your veterinarian because these, these animals
can live productive lives you just have to manage them properly.
All right so the, the next terrible
disorder disease is, is glycogen branching enzyme deficiency
or GBED, and again we see this in quarter horses or other stock type horses.
And what happens in this disease is foals
lack the ability to, to, to store glycogen.
So their muscles and their brain cannot function properly.
So this is always fatal disease, and the, the foals either aborted later.
They're, they're born, still born.
So they actually did not make it through pregnancy.
So, it's estimated that about all ten,
about 10% of all quarter horses are affected
by this disease, and you know, other
bloodlines that have some quarter horse in them.
And again, they trace this back to descendants of King, who's a sire.
So his offspring that, that's how we pass this one on.
And it's, again, it's a recessive mutation, so you have to, to breed two
heterozygote carriers to see this disease and manifest itself.
So there's a 25% chance that, you know,
the pregnancy will, will result in, in this disease.
Okay.
Now, let's switch gears and, and switch breeds,
and we'll talk about Arabians, and, and this one's
severe combined immunodeficiency, or SCID or SCID, is probably
one I'm, I'm glad I haven't dealt with yet.
But it would be pretty terrible to have to deal with this, because
what happens in this disease is foals can never develop an immune system.
And they die within a few months after birth.
Now, we'll cover this a little bit more next week.
We, we call it passive immune transfer, but all horses after they're, or all
equids after they're born, they actually get
immunity from mom's colostrum or, or first milk.
And so by nursing, they actually will receive a few
months' worth of immunity until their own immune systems kick in.
And take over.
Well, in this disease, that never happens.
So these foals will survive for a couple of
months of, after birth, and you get to know them.
You name them and all this stuff, and all of a sudden they get really sick and die.
So it would be really tragic having to deal with this one.
Now, it's estimated that up to 25% of
US Arabians, Arabians in the US may be carriers.
And the articles I was reading they think that might
be a little high, but that's still a pretty big number.
of, of horses that might be, having this.
So, you know, there are, there are Arabian studs that are advertised as SCID free.
You know, so if you're going to breed your animal, you, you
want to make sure you're breeding it to a SCID free stud.
You know, Arabian horse.
Very similar to our other diseases.
It's a recessive trait.
Obviously the homozygous positives, those ones that,
they, they never make it to breeding.
So we see it with the two heterozygotes, and then
you have a 25% chance of your offspring carrying this disease.
All right, and this is the one I, I, I, I detest.
I, I really do not like talking about this one, but it, it, it's really, if you
own a Belgian horse, you really need to be aware of this, or if you ever do.
And that, that is JEB or junctional epidermolysis bullosa.
And it's also known as red foot disease, and it's just
[INAUDIBLE] not one I would, I would ever want to deal with.
And it causes a, severe blistering around the mouth and the hooves, and, and
their hooves can slough off, and it's
just horrific and, and foals are usually euthanized.
This can actually, infect humans or affect humans too.
So it is one out there.
And this is a picture I'd, I'd tried to keep
it as small as I could with, trying just to show
you that, you know, my heart goes out to that
animal avoid what look like, and again a, a recessive trait.
So you want to genetically test any Belgium horse.
That you're going to breed to see if they're a carrier of this.
And if they are, you want to make sure you
definitely do not breed to to another recessive carrier, or
you're going to see, you might, you have a 25%
chance of seeing this, which I hope you never do.
I, I, I, I really do.
Alright.
And then, obviously, there are some other genetic diseases.
You can see the night blindness in Appaloosas and HERDA.
You can see that.
And then the, the PSM we also see in, in, in mainly draft horses.
So, it, it, really, you know, you,
especially with the internet today and, and a
lot of the resources, especially breed registries
are going to have a lot of good resources.
If you're concerned about any sort of genetic disease.
that, that your animal might have or, or could pass on.
So, so just be aware of that.
That was kind of the purpose of this lecture and you know the good
thing is in the future with genetics, and even in my own research here.
It's, it's genetics it's where is at and we are finding out more
and more, specially in the [INAUDIBLE] and,
so genetic testing is, is becoming easier.
It's very you know, relatively inexpensive, generally, and certain
breed registries actually require you to genetically test your animals.
Especially with stallions.
So you know, it's, it's, the future's here and, you know, use it.
Use it to your advantage.
You know, become aware of what's out there, and
you know, have these animals lead healthy and productive lives.
So that's it for week five, and I know this, this isn't the, the most fun topic,
you know things we've talked about, diseases and the bugs and and first aid.
I've really felt this is one of the most important week of the course.
So go back and review everything, attempt quiz
five, you know, go ahead take quiz five,
thi, this is the final week of assignments,
so you can review the health plan video.
kind of see.
Putting together a deworming plan for your animal and a vaccination plan.
And we'll ask you to complete three peer reviews by the end of next week.
And then that would be it for the assignments for the course.
So, so next week we start reproduction,
my, my favorite topic, my area of research.
So, what, we'll have fun talking about that.
And, you know breeding these animals and foaling, my favorite time of year.
And we'll we'll get to something and we'll end the course on a, on a bright
note with the future of, of all of
our equines, so I will definitely see you then.
[BLANK_AUDIO]
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