What are the genetics of flea bitten gray?

[grayarabpony]

How is it different from plain gray?

[goodpony]

I have been told that Flea Bitten Greys are most often Heterozygous....some seem to believe the incidence of melanoma is reduced in Heterozygous greys as well.

[dbaygirl]

...and Heterozygous means..??.. My filly is by a flea bitten gray. Well, he looks flea bitten up close but not in his pictures. I spose it comes with age. She was born bay and is a year old and roaning out.

[RiddleMeThis]

...and Heterozygous means..??.. My filly is by a flea bitten gray. Well, he looks flea bitten up close but not in his pictures. I spose it comes with age. She was born bay and is a year old and roaning out.Only one copy (out of a possible 2) of the gray gene.

The genetic makeup of gray varies from horse to horse, but each one will have a copy of the gray gene.

[JB]

Heterozygous or homozygous has nothing do to with fleabites. They develop based on a separate genetic code, and develop on both types of grays.

[RiddleMeThis]

Heterozygous or homozygous has nothing do to with fleabites. They develop based on a separate genetic code, and develop on both types of grays.
Actually Jb, the researchers who found the gray gene, did actually find that heterozygous grays were more likely to have fleabites. (and a few other things as well.)

[Julz]

I have owned and bred seven greys. Some hetero- some homozygous, but I don't know who is which. Most of mine start dark, go roan, then grey (white) and at about 14 or so, start getting dark 'bites'. Only one so far has stayed all white at 16, the 21 & 22yo got very flea bitten, almost a reversion to their original coat color.

Have fun with your baby!

[JB]

Actually Jb, the researchers who found the gray gene, did actually find that heterozygous grays were more likely to have fleabites. (and a few other things as well.)
Hmm, interesting, so it's a relatively new finding? I wonder if that means that the gray sort of starts to "wear off" after a while because it's not doubled up? :D

What are these "other things"?

[RiddleMeThis]

Heres everything

1. Homozygous grays go gray faster than ones that are heterozygous ones.
2. Homozygous grays have a much higher incidence of melanomas.
3. Homozygous grays have a much higher incidence of vitiligo.
4. And this is the crazy part...horses that are "aa" at agouti have a much higher chance of getting melanomas than horses that are AA or Aa.

[Erin Pittman]

Very interesting, RMT!!! Do you know how much higher the risk of melanomas is for horses that are aa vs Aa or AA? That is weird :eek:

[RiddleMeThis]

Very interesting, RMT!!! Do you know how much higher the risk of melanomas is for horses that are aa vs Aa or AA? That is weird :eek:

Nope I dont. The paper still isnt published as far as I know. I will ask again today or tomorrow. Once it is published we should know more. As of now, thats about all I have. Ill ask about some of the stuff today or tomorrow as well.

[JB]

Wow, fascinating!

I know there was a lot of research going on looking into the melanoma situation in grays, because it was thought/hoped that research would yield some insite into why equine melanomas are not the same as human melanomas, and maybe thereby coming up with a cure for the human variety. I wonder if this stems from that same research? It was several years ago that I read about that particular study.

Since it's known that non-grays can get melanomas, I wonder if someone will find that it's related to their Agouti status?

[Erin Pittman]

Wow, fascinating!

Since it's known that non-grays can get melanomas, I wonder if someone will find that it's related to their Agouti status?

That's what I was thinking...but then it would seem that true black horses would be more at risk of getting melanomas than, say, a bay horse if that were the case (or a chestnut that is Aa or AA). I think color genetics is fascinating! The more I learn the more I'm hooked on learning more - viscious cycle.

[RiddleMeThis]

The more I learn the more I'm hooked on learning more - viscious cycle.
Just wait untill you start planning your entire life and future around them!!!:lol::lol::lol:

I wouldnt know what thats like though....:uhoh:

[dressagetraks]

I know I'm getting hooked. Got to get the broodmares color tested. You learn so much on these boards!

If a homozygous gray has two graying factor genes instead of one, does he have to come from two gray parents? My silver yearling is from a gray and a chestnut, but if he's anything like his sire, and the SO says he is a dead ringer for his sire at all stages so far, he'll be flea bit. So probably he's heterozygous. He is graying faster than a lot of other friends' gray horses have, though. He was starting to change within his first month. Now solid silver with black mane and tail at 14 1/2 months. I like the black on gray effect, but I figure he'll lose the black mane and tail.

[RiddleMeThis]

I know I'm getting hooked. Got to get the broodmares color tested. You learn so much on these boards!

If a homozygous gray has two graying factor genes instead of one, does he have to come from two gray parents?
Yes. A horse gets one gene (for everything, from color to size and back) from each parent.So if one parent is gray and one isnt a horse can only get one gray gene.

[Ambrey]

Interesting!

My gray is already fleabitten on his face, not even fully grayed out on his body. I assume this means he'll "do" fleabites?"

Not my fave color, but I'll survive :)

http://i185.photobucket.com/albums/x182/estarianne/200805-19-Lightning139.jpg

RMT, was there any talk about "average" time to go gray, or how to predict how long it will take? My horse is 7 now, I assume heterozygous (half QH).

[okggo]

I've actually posted about this before (not the flea bites, but the melanomas)

The Equine Veterinary Journal published the results of a study that was done on the malignancy of melanomas in grey vs non-grey equines.

The study found that melanomas in gray horses are less malignant than those found in solid-colored horses. Researchers think that grays have specific genetic factors that inhibit the metastatic processes to some degree. Also, the researchers found that the heritability of melanomas in a gray horse population is about 30%.

Research also shows a higher percentage of melanomas in grays (some indicate up to 70%), but this is a positive finding in the sense that most tend to be under the tail and non-cancerous vs those found in non-gray colors having a higher likelihood of malignancy.

Here is a synopsis from the horse (you need to register to read it)

http://www.thehorse.com/ViewArticle.aspx?ID=4655

and the Journal link (but you actually have to buy it) https://secure.evj.co.uk/cgi-bin/ind...ml?id=kiYwSXCY

Just more FYI

[JB]

If a homozygous gray has two graying factor genes instead of one, does he have to come from two gray parents?
yes - homozygous means "all the same". Since each gene comes in pairs, this means 2 gray genes, which means 1 from each parent :)

My silver yearling is from a gray and a chestnut, but if he's anything like his sire, and the SO says he is a dead ringer for his sire at all stages so far, he'll be flea bit. So probably he's heterozygous.
If he has one non-gray parent, by default he's heterozygous :)

He is graying faster than a lot of other friends' gray horses have, though. He was starting to change within his first month. Now solid silver with black mane and tail at 14 1/2 months. I like the black on gray effect, but I figure he'll lose the black mane and tail.
He will indeed lose the black mane and tail. He's heterozygous gray, but graying pretty fast, which means he's one of the reasons why "homozygous grays faster" is just a generality :)

[Portia]

OK, color people -- so tell me again how you go about getting the horses color tested? :)

[erinwillow]

grayarabpony,

thank you so very much for asking this question! I had asked the same question a few months back on our Connemara chat room and nobody knew the answer, lol!! The best response I got was. . ."it's part of the greying process" BUT, like you, I had noticed that some ponies grey with dapples, some shortly after birth and some took to developing "flea bites" so. . thank you everyone for sharing your knowledge :winkgrin:

[MaresNest]

I have been told that Flea Bitten Greys are most often Heterozygous....some seem to believe the incidence of melanoma is reduced in Heterozygous greys as well.

Well, I'll add my tiny bit of anecdotal evidence for that to the discussion:

I have a flea bitten gray mare who, at fourteen, is melanoma free. She was dappled when I got her at 5 and has progressed straight from dappled to flea bitten. There was no white stage.

[JB]

OK, color people -- so tell me again how you go about getting the horses color tested? :)

Well, the test for gray isn't officially out yet ;)

But, the current places to get colors/patterns tested are (and I might have left some out)
http://www.vgl.ucdavis.edu/services/coatcolorhorse.php
http://www.animalgenetics.us/Equine.htm
http://www.vetgen.com/equine.html
http://www.petdnaservicesaz.com/Equine.html

[sniplover]

OK, color people -- so tell me again how you go about getting the horses color tested? :)

It's fairly simple; you yank a few mane or tail hairs and mail them in to either UC Davis's vet genetic lab (in CA), Pet DNA services of AZ, or the newer Animal Genetics Incorp (in FL). Unfortunately, there is not a test for the 'grey' gene that I know of at this time (nor do any of the websites offer this test)

[Portia]

Thanks for the info. As JB knows, I've like grey and I've got grey :D -- the REAL Portia and now both her babies, full brother and sister who have two grey parents. Which makes them possibly but not definitely homozygous, is that right?

The REAL Portia -- whose sire was bay and dam was flea-bitten -- was born chestnut, darkened, went rose, then dappled, and recently white. At 13 she is now showing some flea bitten spots, but not a whole lot (and no sign of melanoma, thank goodness! knock on wood, prayers to the horse gods it stays that way). Her baby daddy ;) Torino, who's only 8 and whose sire was bay and dam grey, appears to have been a classic very dark bay/black with a steady transition to dappled grey. The colt last year was born bay, and this year's filly was born chestnut, and it will be interesting to see how they each grey out -- and would be even more interesting if I knew their color genetics.

[Julz]

Q: Grey is always dominant, right? So, a heterozygous grey can pass on their non-grey color gene to offspring, resulting in a solid foal that will not grey.

That must mean that one of my mares is at least hetero since she had a solid foal. And my stallion had to have been hetero too, since he had sired solid foals (bays, chestnuts, and black (I think)). And since that mare's parents were both grey, they had to have been heterozygous too. Hmmm. I love genetics...

[Foxtrot's]

My mare is exactly like the Real Portia - except I hate to say it, the vet found melanomas in her anus when doing baby checks. She is also l3. Dammit.

[rcloisonne]

1. Homozygous grays go gray faster than ones that are heterozygous ones.
This has been known, like, forever. Some are even born grey:

http://public.fotki.com/hypoint/arabians/arabian_directory_m/ms_czarthan.html

2. Homozygous grays have a much higher incidence of melanomas.
Makes sense.

3. Homozygous grays have a much higher incidence of vitiligo.
Not surprising.

4. And this is the crazy part...horses that are "aa" at agouti have a much higher chance of getting melanomas than horses that are AA or Aa.
Now THAT is very interesting!

I had a grey (heterozygous) mare who stayed nearly pure white until her death at age 27 (she had a few flea bites but they were tiny and you really had to look hard for them). No melanomas but she did develop vitiligo as she aged. This could only be seen when she was soaking wet and it didn't touch her head at all.

She was born chestnut (I have foal pics as I purchased her from directly from her breeder). My mare's dam was a grey but born bay (her sire, Khemosabi, was homozygous for agouti). My mare's sire was a rare Varian bred chestnut :eek: with two bay parents.

It has been my limited observation, though, that chestnuts who grey tend to stay white while the darker colors (bay/black/brown) become flea bitten as they age. Anyone else notice this?

[grayarabpony]

My pony was born dark bay -- is now fleabitten. Fleabites are chesnut- colored, not dark. It would be interesting to have a survey of base coat color and tendency to fleabites.

That's interesting about the wild type or recessive agouti gene and the link to melanoma -- I did not know that.

[JB]

the REAL Portia and now both her babies,
WHOA. Back the truck UP! WHEN did Miss P have a SECOND baby? You are holding out! Or being sneaky! I. WANT. TO. SEE!! *stomp*

full brother and sister who have two grey parents. Which makes them possibly but not definitely homozygous, is that right?
Right.

[RiddleMeThis]

That's interesting about the wild type or recessive agouti gene and the link to melanoma -- I did not know that.
Incredibly interesting!! I was stunned when I found out!!


Interestingly enough A is the wild type, and a is the mutation.

[RiddleMeThis]

This is a very interesting pedigree as far as gray goes.

http://www.allbreedpedigree.com/gazon3

[dressagetraks]

My boy's sire was born dark bay and went fleabitten gray. My colt also was dark bay, very quickly graying, and the SO says he's a dead ringer for his sire at this stage.

http://i276.photobucket.com/albums/kk8/dressagetraks/MissyToccata4.jpg

http://i276.photobucket.com/albums/kk8/dressagetraks/ToccataWalkingAwayVictorious.jpg

My colt's dam is chestnut, obviously, but she has developed, starting about age 10, a few white spots underneath her chin. They aren't tack-related - she was broken in and ridden for a year, but she's been only pasture sound due to an injury for most of her life. These are round, white spots, about quarter-sized. She's also roaning out just slightly down from her star in the last few years. Where do the coin spots come from?

[RiddleMeThis]

Where do the coin spots come from?
Most likely sabino. They could also be birdcatcher spots.

[galifa85]

What an interesting topic!



It has been my limited observation, though, that chestnuts who grey tend to stay white while the darker colors (bay/black/brown) become flea bitten as they age. Anyone else notice this?

Yes, I noticed that too. I also noticed that the fleabitten spots are usually chestnut (or they just appear chestnut to me?!).

I have a 23year old fleabitten grey arabian mare - heterozygot, with lots o melanoma. She was born bay. Her last foal was a black (or dark brown, maybe seal brown - never tested him) colt with some white spots - Birdcatcher Spots in my opinion. Some of these spots vanished while he aged. He has some white hair on his body (you can see it only if you look for it), but it doesn't look like he will turn into grey and he hasn't developed any melanoma to date. I forgot to mention he is 6 years old now.

[Waterwitch]

I have a twelve year old gelding and his seven year old half sister...both grey.

The gelding was born brown with little white, went dappled, now very very flea bitten - brown, black, and chestnut fleabites.

The mare was born chestnut with sabino markings, went dappled, now starting to get some chestnut flea bites sprinkled here and there. Don't know if she will go completely fleabitten or not. Her 9 year old full sister (also grey) was born bay with little white and is not fleabitten (yet, anyway).

[cloudyandcallie]

I have been told that Flea Bitten Greys are most often Heterozygous....some seem to believe the incidence of melanoma is reduced in Heterozygous greys as well.

I really hope you are right. I have a dappled grey and white pinto turned flea bitten grey and white and I hope we won't get the melanomas I've seen on some grey horses.
My pinto had grey mother and a dark bay and white pinto father. He was dappled grey at 5 yrs, then gradually lost his dapples, and now at 13 he is flea bitten and white. And yes, he's getting more flea bitten this summer, altho he stays in during the day.

[RiddleMeThis]

My pinto had grey mother and a dark bay and white pinto father.
He is heterozygous. Only one parent was gray so since he is gray he only has one gray gene, not two because both parents werent gray.

[Christa P]

My grey was born black, greyed to dappled, and is now fleabitten with chesnut colored specks. I say he is trying to turn into chesnut like his dam was :winkgrin:. I know he is heterozygous because his sire was grey and his dam was chesnut.

Since he was born black I think he is aa for agouti and (from info on COTH) that might make him more prone to melanomas. He does have some small ones under his tailbone and another on his neck in a none critical area.

Christa

[BravAddict]

Yes, I noticed that too. I also noticed that the fleabitten spots are usually chestnut (or they just appear chestnut to me?!).


Well, chestnut and bay are more common than black, so red fleabites would be more common.

[grayarabpony]

The coat color of bay is a mix of black and red. The fleabitten horses I've seen had red spots, shading toward maroon if the horse had a bunch, but someone on the Lipizanner thread in the Dressage forum said that she had a stallion with red and black fleabites. I've seen a pony with a few apricot-colored fleabites (very cute by the way -- I wish my fleabitten horse was that color) -- there's probably genetic variation in how much color can be expressed in the fleabites.

[RiddleMeThis]

Well, chestnut and bay are more common than black, so red fleabites would be more common.

I actually think the order goes

bay
black
chestnut

But I will go look for it. Now Im curious.

[BravAddict]

I actually think the order goes

bay
black
chestnut

But I will go look for it. Now Im curious.

Disagree here. Does anybody know more black horses than chestnuts?

[Ambrey]

Yeah, I'm pretty sure true black is rarer, because of the proliferation of agouti I guess.

[ambar]

I also know an Arabian stallion (Ascendant (http://www.allbreedpedigree.com/ascendant4)) whose fleabites are black on his legs and red on his body, just as if he were bay under the gray. I don't have good close-up pics, though.

[RiddleMeThis]

Disagree here. Does anybody know more black horses than chestnuts?
I do. Still looking for the study I saw.

[RiddleMeThis]

Quick informal survey from dreamhorse doing JUST a color search

Chestnut 7909
Black 6004
Bay 16125

Hmmm maybe I was thinking base color.

[RiddleMeThis]

From Equinenow.com

Bay-5490
Chestnut-2850
Black-2478

[Portia]

WHOA. Back the truck UP! WHEN did Miss P have a SECOND baby? You are holding out! Or being sneaky! I. WANT. TO. SEE!! *stomp*
Here is Interlaken, Heron's full sister. This is from when she was only a few weeks old. She is now three months. You know how it is -- the second child doesn't get as many pictures taken as the first baby. ;)

[JB]

dang, what a little cutie! Really, really nice. That shoulder, that butt! Congrats!

[ambar]

I haven't read the paper yet, but I don't think they discuss flea-bitten. We can speculate more, though! :D

A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse (http://www.nature.com/ng/journal/vaop/ncurrent/abs/ng.185.html)

[Erin Pittman]

Wow! Thanks for the link. Very interesting article (although reading pure genetics lingo sometimes makes my brain bleed). It does talk about flea-bites (not related to agouti status, but higher prevalence in heterozygous grays). If I'm reading it right, agouti status and its association with melanomas still has to be linked with the gray gene (i.e., my former question of whether or not agouti status of non-gray horses might affect melanomas probably doesn't apply).

Brief snip from the article:
The least-squares means (± s.e.) of melanoma grades were 0.88 ± 0.06 for ASIP A/A, 1.06 ± 0.04 for ASIP A/a and 1.22 ± 0.07 for ASIP a/a (P = 0.0006); these estimates are conditional on the presence of the Gray allele.

Any ideas as to when/where the genetic test will be commercially available?

[cloudyandcallie]

my once dappled grey and white pinto turned flea bitten grey and white has the red dapples.
dam was "brown turning grey" at time of my horse's birth, father was bay and white pinto.
we didn't go thru any white stage, just grey dapples turned over 2 years ( when 7 and 8 years old) to flea bitten, and now more flea bitten this year at 13.
I was hoping for all the flea bites to disappear, but y'all were right, they are getting more numerous.
so if he is only 1/2 fleabitten (50% of him is white hair/pink skin) does that also minimize his chances of getting melanomas?
and what influence does the sun have it that, if any? (He stays in during the summer during the day due to sunburning on the pink parts)

[Seven-up]

This is a very interesting pedigree as far as gray goes.

http://www.allbreedpedigree.com/gazon3

Are you talking about the non-grey coming from 2 grey parents? (Or am I missing the boat?)

If you are, I also had an arab that had one of those in the pedigree. I thought if both parents were grey, the baby would always be grey.:confused:

[RiddleMeThis]

Are you talking about the non-grey coming from 2 grey parents? (Or am I missing the boat?) Kind of. More like sire side is gray for at least three generations if not four. Dams side has a lot of gray as well. Just a lot of chances for the to be a homozygous gray, but obviously didnt happen. I thought if both parents were grey, the baby would always be grey.:confused:
No. Not always. Each parent could have either one or two gray genes. If either parent has two gray genes, then they will always pass one to every foal and then every foal will be gray.

If only 1 parent has only 1 gray gene, then 50% of his offspring will be gray.

If two parents ahve one gray gene each, you have 50% of the foal getting one gray gene, 25% chance of the foal getting two gray genes, and 25% chance of no gray genes.

That make sense?

[Seven-up]

A little, but as soon as someone starts talking percentages, I get lost. :lol::lol:

[Portia]

A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse (http://www.nature.com/ng/journal/vaop/ncurrent/abs/ng.185.html)

Stop! My brain is bleeding! ;)

[RiddleMeThis]

A little, but as soon as someone starts talking percentages, I get lost. :lol::lol:
Ok I will do it with numbers.

A bay sire and a gray mare, who has two gray genes have 20 foals. All 20 of those foals will be gray.

A bay sire and a gray mare, who only has one gray gene have 20 foals. 10 of those foals will be gray.

A gray sire, who has one gray gene, and a gray dam, who also has a gray gene have 20 foals. 5 foals will be gray and have two gray genes. 10 foals will be gray and have one gray gene. And 5 foals wont be gray.

Little easier to understand?