Little Steppers

littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

To answer fully your question I need to take into account all 4 possible types I have characterized so far, however there could be more types than these or one of these types could be a combination of two of the four types. Please keep that in mind.
Unfortunately, I do not have my reference pictures on a website so I cannot show them here, and they need to stay off of websites for now, until I can definitively state such differences.

The carriers of types 1 and 4 SOMETIMES[u] show subtle features of a type 1 dwarf, i.e. extremely domed forehead, large prominant eyes, very exotic head overall. That being said however, it is NOT 100% true. In the carriers of types 1 and 4, height is extremely variable, bone structure and thickness extremely variable, length of neck extremely variable. I have samples of parents that produce a type 1 dwarf that really do not show signs in the head and are not very small in height, the only give away was pedigree. However other samples give all of the signs, head, off mouth (usually underbite), build, height, and pedigree.

To clarify 1 vs. 4, the type 1 is the type we see most often, the type 4 is the lethal type that does not go to term.

Carriers of types 2 and 3 so far have shown no signs of being carriers, all so far show extreme variation in height and conformation, the only commonality in structure of the parents so far are overall head structure. They are straight, slightly large for body size, very normal looking heads you would see on a regular horse and ARE NOT exotic. But, they are NOT a straight pony head, i.e. what most people refer to in the pony breed. These characteristics are very general visual differences and commonalities I have experienced and documented, and are not conformational facts describing the disease carriers. They are only observations so far that I see as commonalities with conditions producing a dwarf.

Type 2 dwarf is the type that looks like it has a normal body neck and a large plain or straight head, the dwarf just looks like it had it legs cut in half, in reality the upper leg bones are severely shortened, hips miss-shaped, and a large head. These are the bones and structures that I can tell so far are affected, though I do not have enough samples x-rayed and compared to make that definitive. Unfortunately, this is the type I have seen in the past most often used in breeding progams due to the fact that they still have a mostly normal life and reproductive viability.

Type 3 dwarf is the most severe type that is viable, they are extremely small usually, have severe spine (roachback) and leg deformities, usually severely shortened neck, and severely deformed head with off bite. This type is possibly a combination of types, i.e. inheritance of two different recessive dwarf genes due to the fact that the bodies are so severely deformed and variable it has been very difficult to find a consistent deformed type.

There are some concepts I need to explain about the inheritance and expression of recessive genes to qualify my answers. This is especially important involving carriers of recessive dwarf genes and other recessive deleterious genes, and determining, visually, carriers or non carriers and the problems in doing only that.

One concept is PENETRANCE of a recessive gene over a dominant gene in a population. For example how a recessive dwarf gene's characteristics can penetrate and express the condition over the dominant normal gene's characteristics over a large population. Visual example is a normal horse that is a recessive carrier of the type 1 dwarfism and shows some of the characteristics individually or in combinations, like a severely domed head, very large eyes, under bite, etc. The strict genetic definition is "the frequency, under given environmental conditions, with which a specific phenotype is expressed by those individuals with a specific genotype." So you would see variable PENETRANCE of this recessive gene in the Miniature population, which is what I believe is occuring.

Another concept is EXPRESSIVITY of a recessive gene in one animal. The strict definition is the degree to which an expressed gene produces its effects in an organism. So if you take the example of the situation I explained with Penetrance, you have a normal carrier of a type 1 recessive dwarf gene, and it shows some characteristics of possibly being a carrier, well EXPRESSIVITY is the how much effect is the dwarf gene having on the individual horse to overpower the dominant gene, i.e. slang terminology one might hear is "How dwarfy does the horse look?"

Now you also need to understand the difference of these terms and concepts regarding recessive genes when comparing them to co-dominant genes. A co-dominant diseased gene would ALWAYS be expressed in a carrier with its normal counterpart in equal amounts and NEVER be "hidden". A good example in some flowers is the color pink, it is not a one color but a combination of different colored cells, some are red and come are white, making the color look pink with the naked eye.

If this is a little confusing, you can start another thread referring to this one.

John

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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

Yes short "stubby" legs would make me suspicious especially if other characteristics are there. I know I answered a thread earlier that was on top, my bad, but in that answer, I think from Annette, can give you a really good grasp as to why my answer is variable.

The only time I would be able to look only at legs and say yes is to a type 2 dwarf, where the upper legs are extremely shortened, and a very weak hip. A very good slang comparison to a type 2 dwarf would be to say the body looks like a german Shepard in the rear, and that the body looks like it is going up hill.The biggest problem with using physical visual characteristics is obviously a poorly conformed and stocky horse that is NOT a dwarf might be thought IS a dwarf. This goes back to knowing good horse conformation versus bad and training your eye by actually looking at horses that are known dwarfs and looking at the parents and comparing those visual characteristics and clues and compare to a generally "good quality" horse that shockingly had a dwarf. Again it is something that is learned from experience, and most people dont have the luxury I have had for over 28 yrs seeing from the beginning "dwarfs" from "non-dwarf" carriers. There are numerous consistent characteristics, but pedigree knowledge is the key.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

From what I have personally seen, no there are not any bloodlines that produce "more" dwarfs than others. It is spread throughout the industry involving all of the common foundation stock bloodlines with all of the different type of dwarfisms.

Because this "breed" came from a relatively small number of foundation stock, and that a large amount of inbreeding was and still is being done, we have basically stirred a pot of stew that is on the verge of becoming rank, not adding anything new or fresh, not that it needs to be any other breed. If we just learn that some horses within our own breed can keep us from having that happen. Remember, a vast majority a the Miniature horses in the world have some common foundation stock somewhere, and even if they say unknown up close or farther back, we all know the practices of some breeders back in the beginning.

My example I always give is the 25% of the foals from 2 dwarf gene carriers that do not have the dwarf gene whether tall or small. You dont know which ones those are, but IF some carriers are small and some small horses are not carriers; and some tall ones are carriers AND some tall ones are not WHY not keep them ALL?? We are slowly getting rid of half of the 25% normal ones that just so happen to be tall, and they will NEVER produce a dwarf, they do NOT have the defective gene.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

There are no known or proven environmental causes to any of the dwarfisms in the Miniature horse.

The reason why this would be impossible for any of the dwarfisms to be due to a specific environmental factor is that it would have to be something to cause the exact mutation every time in every dwarf produced and it would have to occur all over the world.

These dwarfisms are seen in other parts of the world, and in Canada, and all over the US. The statistical chances of a single environmental factor to cause an exact mutation in the same gene to cause the identical physical condition of dwarfism all over the world for just ONE of the types I have characterized is just HUGE. This means hundreds of millions or hundreds of billions and more to one. I dont know how one would even try to calculate those chances. You would have to take into consideration all possibilities of the variances in concentration, quality, and mutagen power of the environmental factor throughout the world, all of the variations in the number of genes in the horse, the total number of genes, the horses genetic incompetetence of the DNA healing process of the fetus or mare and its eggs during oogenesis and the stallion for semen during spermatogenesis, variations in other mutagen causing agents that could enhance or restrict the specific mutagen envirnmental factor, and on, and on, meaning you have a much higher chance of winning every lottery in the US than that occuring in the Miniature horse all over the world to give you all the same dwarfism seen.

Now there are known environmental mutagens in the world that are known to cause some types of dwarfism in certain organisms, but those are shown to be very specific within a certain local area, meaning, isolated areas with organisms experiencing the exact same environment with the mutagen causing factor, i.e. a single farm with a mutagen causing agent on the farm, also chemicals or environmental factors that cause metabolic diseases in an organism are already developing, and these still are isolated cases.

I hope this helped.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

You mentioned in an earlier post on the main forum that there is more than one dwarf gene type. I know that dwarfism manifests itself in more than one way but I am thinking that is not what you are referring to. Or is it? Are you thinking that a given gene will always produce a minimal dwarf and so on? "

Each dwarf type, if they are definite different types will most likely involve different genes for each type. This means type 1 is caused by a mutation in gene A for example, and type 2 is caused by a mutation in gene D, and so on. So there is not a single dwarf gene for all the types and the gene is then changed differently to cause the different types, that most highly unlikely to be happening. This is given that in other animals similar dwarfisms to what I see in the Miniatures are occuring and they involve different genes respectively.

First there really is no "minimal dwarf" that has become a slang term for carriers that show alot of characteristics of dwarfism, and for dwarfs that are very "good". If you dont know if the horse is a carrier, are you sure it is just not bad conformation, again some people can be quite wrong sometimes, and most of the time they can be right. This is all subjective right now.

There are normal horses with a recessive gene that might show some expressivity, as I explained in another thread, by Annette. The horse carrying that recessive gene is normal, in a sense. And a dwarf that is a "good" dwarf is not any less of a dwarf than a more severely affected dwarf of the same type, they are both homozygous for the dwarf gene. Again the expressivity manifested itself differently in each one, same as seen in humans.

"If the gene types you are referring to are in fact indicators of something other than dwarf types, what is your research suggesting the significance of that might be for owners/breeders? Given what you know today, does that alter what we need to be looking at/for in our own animals and when purchasing new stock?"

That question doesnt apply I think with what I wrote above. There are probably 4 different types of dwarfism probably caused by 4 different genes that have been altered from normal somehow. There is a possibilty that some of these dwarfisms , I think maybe type 3, might be a combination of two mutated genes that cause a type of dwarfism. Again this is all circumstantial to my findings.

The significance of my findings for breeders is that we will be able to improve this breed very quickly if the diseased genes are found and tests can be made. I do not believe carriers should be totally eliminated if that is what yo are asking. I believe we should look at what other very smart horse breeds did with diseases within a large population of a breed, i.e. HYPP in the Quarter horse.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

Ok,

If you read my reply to Frank on the forum, I talked a lot about this. I do not have a "cut-off" I do not know what it would be or even how you could calculate that statisically, knowing that height is a quantitative trait, irregardless of the effect of the recessive gene, if any. Again what we all talk about is all highly subjective with height and being a carrier. Especially since I see tall minis with normal heads produce type 3 dwarfs.

King Supreme never produced a dwarf, statistically, he has a 99.99+% chance of NOT being a carrier.

Double Destiny never has either and it is even higher than that a 99.999+%, of not being a carrier. This is because I have bred him to known carrier mares of different pedigrees and inbred him into his pedigree a lot, and bred him to a daughter.

I know of overs, well over that have had a dwarf bred to a smaller carrier, so it really would be impossible to have a tall cutoff point given the fact that there could be a homozygous normal 25" (non-carrier) horse out there somewhere.

The only thing I do know is that I have yet to hear of a pure bred Shetland pony or Hackney any type of dwarf, especially not anything that looks like what we see in the Minis.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

It is unfortunately impossible to know those numbers. This is due to the fact that some people do not admit that they have them, records are not kept on dwarf foals born, aborted or anything by the Assoc., so there is no way to know how prevelent these types are. I do have my educated guesses, but I will not give those out specifically with regards to the populations I have dealt with, meaning breeding programs. This is because it is so subjective to only those horse populations I have dealt with, so those numbers would be skewed and not reliable to a population as a whole if you want me to include the horses up to 38" that have "some" Shetland close in their pedigree.

I will say this, with including all of these 4 dwarf types combined in the total population, and knowing the inbreeding done in the past and now, I would not be suprised if it is involves 1/8 to 1/2 of the total population, including those up to 38".

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

There are no known dwarf genes identified in the horse genome, meaning all horse breeds, compared to the dwarf genes known in the human. There are numerous known dwarfisms that are characterized and sequenced in the human, mouse, and cattle. These are what I am using to compare to as candidate genes.

I am the only one I know that has the samples needed, the pedigrees, and other inheritance pattern info needed to do this right. What I am doing is using the candidate gene approach to try to find the dwarf genes in the horse, which really are normal genes that have been mutated. This approach uses known genes in other mammals that have been found sequenced and characterized as producing a specific dwarf disease. I then try to see if certain known mammal dwarf diseases characterized, match as close as possible to the PHYSICAL characteristics of these dwarfs to then take that known gene and then compare it to the horses unknown gene. Each try is a true shot in the dark, that is why physical characterization, ie, digital xrays and necropsies are necessary to keep the shots in the dark to a minimum.

Right now I feel there are mutiple genes involved to cause the different types seen. meeaning one defective gene one type of dwarfism.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

OKay this is going to be more of my ethical and caring, personal opinion and less of my scientific opinion.

Science opinion would be to not breed them, the quicker they are removed the quicker we can breed dwarf free Miniatures.............,

HOWEVER and BUT!!!!!![u][i]

We cannot punish breeders that have bought, bred, invested into horses on a false pretense, ie unknown genetics. It is in essence noone's fault currently, we have to look at the past for blame, and that can only be to look at our past history and move forward. Removing certain horses might be financially acceptable to some, others no, and some horses that are carriers have such an overall positive impact it would actually hurt our progression of the breed.

I do not believe ALL horses that have produced a dwarf be removed from a breeding program. In a perfect world with no consequences that might work. I'm just glad no higher power decided to do that to humans. We made this mess, God didnt, directly. We were the hands-on managers.

This is not cows, we cannot send them to slaughter like they did to "remove" the dwarfism in the Hereford and Angus breeds.

That being said, I believe WHEN the dwarfisms are characterized, sequenced and testes developed, we should teach our members what to do to breed the diseases out. We should label carriers on their pedigrees and NON-CARRIERS, and if someone wants to breed to carriers, remember, these are possessions owned by humans, legally we cannot keep anyone from doing anything with their possessions as long as it is not abuse.

Now all you PETA people can sit and rotate, breeding horses carrying a diseased gene is not abuse, how many of you PETA have a recessive or DOMINANT diseased, undesired gene that should not be perpetuated??? Should you reproduce, since you feel animals have the same rights as us??

Now if a dwarf is born, it is the owners decision what to with it. I have my protocol, some have a different one. I just hope you give me a call.

Also, breeding carriers to non-carriers will NEVER produce a dwarf. The non-carrier only give normal genes, and the carrier will only give a dwarf gene 50% of the time; so 50% of the resulting foals will be 100% normal and NEVER produce a dwarf, and the other 50% of the foals will only be carriers.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

Could you summarize for us the most common health issues associated with dwarfism? Also, what is the average life expectancy (I assume it is significantly shortened)?"

The only common digestive issues that I know of for all of them except the type 2, is colic, impaction, and eating/chewing problems, obviously the most common disease issuescaused by the diseased gene is the prominant leg, spine and hip malformations. These problems besides the teeth and jaw, will be the ultimate cause of the majority of their pain and problems from their malformed joints, arthritis, to malformed hoof growth, malformaed leg and other bone growth, restricting their movement and mobility.

Life expectancy is shortened, depending on type, and care, some I have seen live into their double digits, ie 10 or more, but a vast majority I see only living from a few days, months or a few years is all.
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

It is due to the same inferior genetics being stirred continuously in a festering pot, so to speak.

Line-breeding or in-breeding can be really, REALLY good and it can be really, REALLY bad. That said, the really bad resulting horses years ago were not culled from the programs, because the ones that were small and most likely not that good of quality were quite possibly dwarfs. The small size was strictly the goal. If they had been culled due to their poor conformation, we might not have the problems as bad as we do today.

I am going to preface this with in my opinion.

As I said in another thread, there are a small number of small (height) homozygous normal horses being kept, but the taller homozygous normal horses that might be over 34" are kept OUT of the largest registry. Therefore, only half of the homozygous normal horses are kept in the largest registry, AMHA, this INCLUDES all other international registries, except the AMHR.

I hope some of them are reading this. We really need to learn as much as we can about the genetics of the Miniature horse and not some arbitrary height limit set by some breeders in the US(not all of them) that had goals that were not for the best conformed smallest horses, just the smallest animal that kind of looks like a horse. The original "Midget Pony Association" was to measure the horses at the withers 36" and under, from what I know from the past. So I would think if our forefathers were able to "compromise" in the foundation of this "breed", then I would think they would have an interest to compromise even today knowing the genetics of today, not in 1978. This "breed" has become a world-wide love of the small equine. We have the ability to actually make what was started MUCH better. I step will down now.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

Someone asked a similar question on another thread, and no there is not a single ounce of documentation about any numbers of the dwarfs not only in the US but in the world. So the number of dwarfs that I have accumulated is not at all able to be used to calculate or project the total number of cases that might be occuring. The reason is that so many people are out there saying they have a dwarf but are unwilling to give any info about it. However, they still want work done to find a test so they never have one again.

My calls for help usually result in a small number of individuals that get the "big picture" that are willing give me the things needed, ie blood samples of dwarf and parents, pictures of all three, and pedigree info.

On the Best of the Lil beginnings forum right now there is a thread with info about all I need for my research and people that frequent this forum often STILL ask if anything is being done and is there anyone doing research, I just dont get it.

Most of the others will tell me they have one but are only willing to give me a picture, which is worthless for genetic research, or just a blood sample of the dwarf and no other info, especially no pedigree or parent samples. Unfortunately those "random" samples I get, go into storage to be used AFTER I find the gene, mutation and a test, to confirm their type. So they are not able to be used in the pilot study.

And even after my call outs for samples, I continuously see people on the forums say they have dwarfs but are not any of the people that responded to me, so sometimes I just wonder, how many people whine and cry about the problem and say that something needs to be done, then when they have a chance, ooohh, well, dont include them, they dont want to have anyone know who the dwarf's parents are or whatever.

Sooner rather than later we will know a whole lot, and tests will be out there. So just realize if the test is out there and people dont have their horses done then you might wonder why, because I doubt very highly that the registries are going to require any dwarf tests when they come out. I really think they will
try to take this as slow as possible.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

First what usually happens in all animals are known genetic mutations that occur that are referred to as non-deleterious or silent mutations, which occur all over the body including in germline cells, ie sperm and egg cells. They are usually harmless to the organism. However sometimes, there are mutations that occur that can have bad results, some of those mutations can be cancer, etc, and some can occur in germline cells that result in diseased offspring due to a dominant mutation, or offspring that has a recessive mutation and appear normal.

What most likely happened in the Miniatures is that some germline cells in some horse many years ago, mare or stallion, most likely a stallion or stallions, since they have high germline mutation rates and since there are different types of dwarfisms, produced sperm that conceived a normal looking foal that had a recessive mutation. This could have happened to more than one horse, mare or stallion, we do not know, and will never know, EVER, the root cause. Anyways, the resulting foal later bred and passed on this recessive mutation to 50% of its offspring, and so on, and so on, until sooner or later related horses were bred together carrying the recessive mutation and 25% of the foals were dwarfs. That is why highly inbred animals quickly display recessive deleterious traits, an inheritance fact well known and documanted in animal breeds. It is well known that severe inbreeding increases genetic abnormalities seen in resulting offspring from recessive traits.

Later those dwarfs were bred because they were very small, which is very likely what was done early on due to the small numbers of miniatures that existed. Perpetuating the gene.
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

"Do you feel that continually breeding the same lines to each other contributes to dwarfism?"

wpsellwood,

To strictly answer your question yes, it is now and will continue to contribute to dwarfism.

Why?,

It is due to the same inferior genetics being stirred continuously in a festering pot, so to speak.

Line-breeding or in-breeding can be really, REALLY good and it can be really, REALLY bad. That said, the really bad resulting horses years ago were not culled from the programs, because the ones that were small and most likely not that good of quality were quite possibly dwarfs. The small size was strictly the goal. If they had been culled due to their poor conformation, we might not have the problems as bad as we do today.

I am going to preface this with in my opinion.

As I said in another thread, there are a small number of small (height) homozygous normal horses being kept, but the taller homozygous normal horses that might be over 34" are kept OUT of the largest registry. Therefore, only half of the homozygous normal horses are kept in the largest registry, AMHA, this INCLUDES all other international registries, except the AMHR.

I hope some of them are reading this. We really need to learn as much as we can about the genetics of the Miniature horse and not some arbitrary height limit set by some breeders in the US(not all of them) that had goals that were not for the best conformed smallest horses, just the smallest animal that kind of looks like a horse. The original "Midget Pony Association" was to measure the horses at the withers 36" and under, from what I know from the past. So I would think if our forefathers were able to "compromise" in the foundation of this "breed", then I would think they would have an interest to compromise even today knowing the genetics of today, not in 1978. This "breed" has become a world-wide love of the small equine. We have the ability to actually make what was started MUCH better. I step will down now.

John
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littlestep · dig a grave!! Joined: 19 Feb 2006 Posts: 4986 Location: TN

Yes, there are carriers of the dwarf genes that I see are stocky or heavy boned, but I see just as many that are extremely refined.
Personal example, I foaled out a mare about 8 yrs ago that was a retired mutiple world champion, extreme in all the characteristics and an awesome mover for her height, she is 30". Her sire was a known carrier, she was bred to another world champion, but he was 28", relatively refined and young and his pedigree had known carriers in it. His first or second foal crop was her foaling yr, cant remember which but anyways, it was a dwarf, and it was her first foal. Though the dwarf was refined comparatively to others I have seen, it was still a dwarf type 1.

So again you have refined bone structure having a slight influence on the disease just as the disease when carrier recessively has a potential to peek out in some characteristic, again goes back to penetrance and expressivity of the gene in a variable population, especially one like the minis with extreme variation of bone structure and size.

John
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