regarding your last sentence… Maybe you should at least try to understand what I say… My original statement meant exactly that… But obviously some of you chose to interpret it different… Not my fault…
WBs are not exactly a restricted population. it is multiple registries. i would by no means call WBs a restricted gene pool because of the amount of criss-crossing registries do.
so i would not say it compares at all to aussies (or that the same principles apply), who only accept offspring of papered aussies into the registry.
besides, that is not how genes or inheritance work - if you cull a “bad gene/recessive allele”, another “bad gene” does not automatically rise to take its place. the goal would be to replace the recessive allele with a “normal” non-carrier-status allele.
the other thing is that, in many cases it is not just one allele - sometimes its several - we know enough about many hereditary diseases that sometimes it is a combination of genes that cause a disorder, even though it only takes “one carrier” copy to inherit the disorder.
that article is from 1998 - as far as genetics go, it’s quite outdated.
9 Likes
the underlying principles are still the same at least that’s what the geneticists at VGL insist. Its not that bad genes suddenly appear its that they are already present within every population/individual.
1 Like
But “bad genes” do suddenly appear. They are spontaneous mutations. HYPP, HERDA, GBED, Lavender Foal Syndrome, Frame, and all colors/patterns/dilutions other than “bay dun” are mutations for horses. New W (white spotting) mutations appear on a regular basis. Some genes, such as KIT, mutate a lot more than others.
The gene itself didn’t appear, to my knowledge horses don’t suddenly develop another set of genes. But their form can mutate in a variety of ways.
4 Likes
I think the difference between types of genetic diseases are being blurred here.
HYPP is an autosomal dominant defect, meaning that horses with one copy of the defect are not only “carriers” they are affected by the disease. Some can be managed. For others, the condition in its heterozygous state, is fatal.
HYPP should not be compared to WFFS, HERDA or the Frame mutation or any other recessive disorder. It is not the same situation for breeders or horses, at all.
UC Davis has done a great amount of research and has plenty of educational information available online about HYPP, if anyone is interested in understanding the difference.
For what it’s worth, I think Hilltop has made a very responsible decision to hold off breeding this season, until more is known about the disorder. No harm in that.
10 Likes
As someone who owned an HYPP+ horse (+/-), yes. He suffered because his breeder thought the HYPP gene would make him a better halter horse. And he did suffer whenever he had an attack. If you own a carrier, enjoy it, but don’t breed it.
Before people knew about the dominant nature of the disorder, they thought horses could just be “carriers”.
4 Likes
I think you are missing one of the points people are trying to make. xQHDQ makes it well. When HYPP was first figured out most of the breeders were like some of the people here. “How dare you restrict breeding, this is my livelihood” and “carriers are fine so no reason to not breed for carriers”.
If people had waited for a little more research they would have known that even carriers have an issue.
Though clearly that does not stop people from making stupid breeding choices and intentionally producing foals with an issue.
8 Likes
Oh, I remember those days very well. Even when it became known that N/H horses were affected they kept on breeding and selling them, often without testing and no disclosure.
The sight of a distraught young girl watching a beloved horse die in its stall is with me to this day. She stopped her involvement with horses she was so traumatized, and her parents were livid when it became apparent that the breeder and seller knew the horse was N/H. He had to be, as his sire was H/H. and it was later determined that the mare was N/N. It was quite awhile before testing was required and required to be recorded.
The mishandling of the HYPP situation is a shame, an example of greed and disregard for horses, and people in the horse world, at its worst.
I agree that xQHDQ explains the issue well. Yet people keep lumping these defects together and they are not comparable.
As I said in an earlier post , I think Hilltop is wise to wait until more information is available before continuing the breeding of the carrier stallion. Well done them.
2 Likes
The same mutation didn’t suddenly appear in multiple horses at one time, though. All of those genetic flaws could have been eradicated when the number of horses carrying the mutation was quite limited, if the effects were known and tested for, and the affected (very few) horses were never bred.
Thanks to records, we know that the mutation of the Y gene that starts with some single descendant of one branch of Eclipse in thoroughbreds, has now “taken over” sire lines in the vast majority of European horses with TB sire lines. It has virtually driven out the previous, unmutated Y chromosome. One suspects that it provides some unknown benefit to have been so successful. The same is true of the C allele with the American indel on the MSTN complex on Chromosome 18 that is driving out the T allele in thoroughbred racers. Its benefit is known now and bred for.
2 Likes
Of course 
All of those genetic flaws could have been eradicated when the number of horses carrying the mutation was quite limited, if the effects were known and tested for, and the affected (very few) horses were never bred.
In theory, yes. In the case of HYPP or any other disease where certain management practices can make the presentation of the disease lesser or greater, it might take some time for someone to start putting pieces together.
Compound that with the fact that Impressive was a very successful Halter horse and as a result, booked a LOT of mares, so right off the bat you had 3-4-5 generations of offspring at roughly 50% carrier status before any of those offspring became old enough to have a reasonable chance of starting to show symptoms. By that time, many of those mares would have also been bred at age 3-4, and some of his stallion sons also booking mares, so by year 4-5 from Impressive’s first year of breeding, you’re already on a 2nd generation with even more carriers. He was born in '69, and it took until the early 80’s for dots to be connected, at least by enough people to start making a stink about it. Even if it was the late 70’s that someone started going Hmmmm, that’s a huge number of descendants, with probably a disproportionately high number of mares and stallions bred (that is an assumption on my part), because they exhibited the bigger muscling often caused by the disease, not to mention how much line- and in-breeding was done in an effort to double up on the “big muscle” genetics of Impressive, creating more and more HH horses 
And even then, it likely took several more years for enough carriers to show enough symptoms that were serious enough for someone to start connecting some dots.
That’s the problem with a disease that can take years to manifest, unlike WFFS or LWOS which makes itself known right at birth.
Thanks to records, we know that the mutation of the Y gene that starts with some single descendant of one branch of Eclipse in thoroughbreds, has now “taken over” sire lines in the vast majority of European horses with TB sire lines. It has virtually driven out the previous, unmutated Y chromosome. One suspects that it provides some unknown benefit to have been so successful. The same is true of the C allele with the American indel on the MSTN complex on Chromosome 18 that is driving out the T allele in thoroughbred racers. Its benefit is known now and bred for.
For sure, breeding TBs for a very specific trait has totally eliminated an entire set of genetics from the breed and greatly narrowed what was once a much larger gene pool.
2 Likes
“Impressive Syndrome” (HYPP) was known for a long time before people raised a stink, pretty much forcing the AQHA to do something. Because of their success in the Halter Ring, it was actually bred for.
1 Like
I’m happy to read so many responses on this thread. We know WFFS certainly isn’t the largest concern for breeders today, and it is hopefully limited to a very small segment of the population to date, but there is much we don’t know about it. Any options to prevent the loss of foals should be of interest for breeders and sadly Warmblood Fragile Foal Syndrome, or the fact that there was a test available, was not on the radar for any breeders I’ve spoken with before this release.
One topic not really being highlighted in this thread that I want to draw attention to is the recommendation for breeders to test their breeding stock. Right now, the estimates on carrier status are based on studies off of relatively small populations. We could find carrier status much lower or higher. With almost the entire breeding population untested, the only immediate positive move we can each make is to test our own horses.
Testing is actually really simple (hair sample) and inexpensive ($55). Animal Genetics is running the testing – you get the results back within a few days. We’ve now tested all our broodmares and future breeding stock. http://www.animalgenetics.com/Equine/Genetic_Disease /Index.asp
34 Likes
A comment on breeding and spontaneous mutations and the business side of things. De novo mutations can and do happen at any time. Sometimes they’re harmless (white mismarks, where what should have been a sock on an ankle wound up being a white patch on a shoulder), sometimes they’re obvious bad, and sometimes you don’t know it’s there until it’s there.
The Australian Thoroughbred Shellscrape, who, despite being a Gr1 winner whose pedigree is a who’s who of top-notch colonial breeding, was retired from stud after only one season after about a quarter of his foals were born without tails. http://www.stallions.com.au/stallions/a_stallion_details.php?arion_id=103365907
Shellscrape didn’t serve many mares in his one and only season at stud–only 14 named foals–but at least 8 went on to be winners and some won well over Aus $100k. In short, the foals were doing their job as racehorses, but as a stallion, he became a kiss of death in the sales arena (important) and any foals he had would be shunned as breeding stock. For everyone involved, him siring foals with physical defects wound up being a big money-losing proposition. The stud farm lost money on the syndication deal, the mare owners lost value in a year of their mare’s breeding career, and the foal owners lost the value of their horses as potential breeding stock.
So it is here. Hilltop Farm as a business is doing a good thing for its customers – mare owners – by taking positive steps to help avoid preventable losses, even if it means a loss to them in the meantime.
I use Shellscrape as an example because it’s a good analogy…having no tail didn’t hurt the individual horses, but nobody knew what would happen if they were used as bloodstock. Manx cats and corgi dogs have degrees of taillessness…in Manx cats, breeding two cats with no tail at all (rumpy) leads to fatal neurological defects in the kittens. A Stumpy and a Rumpy can be bred and have a good likelihood of litters free of neurological defects. Nobody knew if the de novo mutation that caused the taillessness would have knock-on effects in further generations.
9 Likes
The main thing we need to create in all breeding populations is a culture of testing and disclosure. When we find these defects, fund the research for testing, and then individually doing our part to test our breeding animals. Stallion owners can insist that all mares are tested as part of the breeding contract. Mare owners can insist that they will only breed to tested stallions. The tests are simple to have done and inexpensive in the grand scheme of making foals.
We just need to remember that we don’t have tests for everything, and that as always eliminating breeding individuals on a single trait is not always beneficial, if there are other genes in that individual we want and need. Certainly in warmbloods there are so many outstanding stallions that it’s hard to see the rationale of breeding to carriers when there are probably already non-carrier close relatives of similar quality available. As a general rule, though, in smaller populations there are examples of culling carriers that have ended badly, increasing the prevalence of other genetic problems. That, plus the concern that people will simply clam up and not test, are the reasons people express caution about draconian choices for carriers. If people are smart about it, there’s no reason for an affected foal to be born ever again, and that should be the first goal.
I hope too that people will participate in the research and a database can be made of non-breeding animals and their status, so that carrier prevalence and effects can be ascertained.
5 Likes
Laurie means that the dam and her ancestors can/ought to be inspected for evidence of horses being bred even after they had produced one foal with the syndrome.
I think Hill Top is doing great in terms of being honest and trying to steward the gene pool. But! The defect itself-- which kills foals (or makes you euthanize 'em) PDQ is a pretty hard problem for a breeder to ignore. It shows up very early and is lethal. It can’t, for example, be written off as bad “nurture”, nor does it show up well after the horse is in work.
4 Likes
With all due respect, that will increase the frequency of the deleterious allele in the population at large.
I know (or read?) that you think the value of the stallion’s other heritable traits make him worthwhile… even if we have to work around a condition that kills some of his offspring soon after birth. In other words, there is a pretty intense selection pressure against this allele and if this were a sufficiently small population in the wild, a recessive trait that was this bad would take that stallion out of circulation, no matter how great his other attributes were.
But whether or not those other traits can only be kept by keeping him, or whether we can keep some of those traits (or some combination of them) by using some of his relatives depends on where all of those alleles are on chromosomes and the breeding pattern behind the stallion and his relatives.
Holy moley, those are both very complicated problems to figure out! I don’t think we are very close to know their answers for horses.
2 Likes
If you read the email, Hilltop was asked if their stallions were negative because a breeder had a positive mare. They found out the mare was positive the hard way. The sire of the dead foal’s owners are not as forthcoming at this point. That is the other half of the equation.
8 Likes
Super-awesome. But why would you think that horse breeding can be so well-controlled, especially in the US? We don’t have a track record of thinking about altruistically about culling our own animals for the good of the breed.
If I may, I think I can summarize the two conflicting points of view and describe precisely where they blow by one another,
-
Concern for the individual animal without respect to its offspring or the interbreeding population at large. These are the folks who wonder about the selective value of this gene in its heterozygous state. They reason that if it’s benefitting the animal (or at least not harming it), there’s no reason to do the vigorous testing and culling of the recessive allele. And so, if follows, that there’s no problem letting the allele continue to exist in the population. Rather anyone breeding their heterozygous animal just needs to make sure to cross it only with a homozygous dominant one.
-
Those who think in terms of an interbreeding population. I am in this camp. I don’t consider the question about the well-being or greatness of the heterozygous animals. I also don’t trust breed registries or even “unregulated” breeders to follow the plan Manni suggests where everyone knows the genetics of their animals and chooses only homozygous dominant ones to breed to. Furthermore (and the reasons that population-level thinkers like me wig out) is that the more you rationalize leaving heterozygotes in the population, the more of those recessive alleles are around, too. So I can picture a scenario where a would-be breeder can’t find a homozygous dominant animal to cross with their much more common heterozygous one.
Did I fairly summarize each side’s point of view?
4 Likes
You are correct, but there are some mitigating factors.
- How large (and, really, how genetically varied or diverse) is the interbreeding population? If it is large, the allele (a version of gene which, in this case is recessive and the disease involved is tied to just this disease; people in this discussion are also using “mutation” as a synonym for allele and for gene), will spread slowly (assuming it’s non-lethal when in heterozygous form. If, however, the individual holding that allele is bred far and wide, it will reach more descendants/future members of the population faster. And third, if the population already had lots of that allele in it (many individuals were carriers), the allele would spread faster, but you’d also see more of these cases where the heterozygous state appeared in the form of a sick foal.
The beauty of this discussion is that the disease in question and genetics behind it is so simple as to work as Gregor Mendel considered. Google up Punnett Square and you’ll see the logic (at least in one generation) and the percentages.
The reason people in this discussion are curious about how researchers got to that estimate of 6-11% of horses being carriers is because that’s a problem that’s methodologically hard to estimated the size of an interbreeding population like this one. Would that be all WBs? All WBs plus any non-WB someone might cross with a stallion like Sternlicht?
But population geneticists work on this kind of thing (and do it quantitatively) all the time. People calling that number a “guestimate” are perhaps not giving that field enough credit for being careful and thorough in their approach to a very difficult research problem.
- The speed with which an allele like this one would spread in the population depends on the frequency with which breeders use the animals that carry it.
I think you could perhaps reach a “happy medium” kind of policy by prohibiting the use of stallions with the recessive allele but permitting mares who carry it to be bred (but not using embryo transfer). Because each mare can leave many fewer offspring during her lifetime than can a stallion, even if she were very prolific her descendants would spread that allele through the population more slowly.
- The nature of this disease intersects with the standard structure of a breeding contract. It sounds like the affected foals can’t “stand and nurse”… or look pretty bad doing it. And so the stallion owner instantly looses his money should a homozygous offspring show up. In other words, not only does the disease show up “on time,” given the way these agreements are written, but it kills the foal.
IMO, this looks like really really intense selection pressure against that allele.
1 Like
