Wow, lots of thoughts out there.
This is John Eberth, your Association's Genetics committee Chair and currently the only one I know that is actively doing actual lab work with Miniature horse dwarfism that has some idea of the breed and its unusual REAL history.
Yes I am the "Little King man" as inferred above
actually I am the Arion man HAHAHA
I am responding to this thread because of the numerous people that asked me to give my thoughts on this issue and where it all stands currently. This might help people think about this sensitive issue in a more genetic perspective. To comment on briefly some of the thoughts mentioned, I desperately want all to know I am very much wanting the best for this breed LONG TERM. Myself and my family are financially very involved in the long term success of this breed so anything I find or do is NOT politically or financially driven. I want our breed to be able to improve and produce more reliable horses in type and conformation. That is what a breed should strive to do, but not destroy itself due to problems that can be corrected over time with education and knowledge.
AQHA was very careful and very thoughtful about their response to HYPP. IT was NOT an instant cull process but a long term process of requiring horses with Impressive in a horse's pedigree, when it was registered, to be tested for HYPP. This was because Impressive was the horse with the originating mutation. If someone is interested I just completed a review paper for a genetics class about HYPP that is very informative about the disease and what is done about it.
This DNA test result is put on the horses reg. papers. No questions asked and no choices. You have to do it BUT, these horses that are carriers and heterozygotes were allowed to be registered and bred. But homozygotes are not allowed to be registered. With this knowledge and the Association's work to educate the members about HYPP and how to breed it out meant that the breed did not suffer a tremendous financial loss immediately or long term member financial loss. That is important because it was estimated that in 1999 there was approx. 60,000 horses with Impressive their pedigrees. Culling all of those horses, which some were top winning and producing sires of the AQHA of all time, would have put that assoc. under great financial strain, not including the members. The HYPP test was designed in 1992, so that tells you that it could have been more rampant in the breed without a test and the breeders could have just swept it under the rug so to speak. and had many more by 1999 had they not been agressive in their SUPPORT OF RESEARCH!!! Oh by the way, in 1992, it estimated that only 4% of the Quarter horse pop. at that time had the disease. Since the advent of the test in 1992, the numbers of HYPP heterozygotes went up becasue of the number of horses tested but after all had been done the breeding management was used to slowly breed the disease out and they are on their way, and the AQHA is one of the most successful horse breeds in the world. Also there are many other registries that have the Quarter horse Impressive in the pedigrees, i.e. Cutting Horse Association, Reining Horse, Appoloosa, Buckskin, Palomino, Paint, Pinto, I could go on. So it is very important how they deal with it. We should do the same, be VERY CAREFUL!
With this in mind, and knowing how many dwarfs are out there now and that have been and how many different pedigrees that has produced dwarfs, if there ever is a test for any of the dwarf types, (and there are at least 4), I would not be suprised that at least 50% or more of this breed are carriers of any one or more of the types of dwarfism. WOW think about what that would do to our breed if we had to cull those immediately. We might as well all sell out now and breed lab mice instead.
We need to understand that it is NOT polygenic. Polygenic means that there are mutiple genes involved in one disease or characteristic trait. What is thought is that there are multiple different dwarf diseases with each having a possible different gene involved for each different disease. I have characterized POSSIBLY 4 different types with at least four different candidate human genes with homologous phenotypes as matches.
Now it is possible for one dwarf to have two differnet dwarf diseased genes and express both of them. This again is not polygenic but a horse with two different disease genes being expressed at once.
Also, I do not know of a human genetic dwarf disease that does not show signs until later as a result of older age, there are over 200 types of human dwarfisms though I will have to see. As for these seen in Minis, these are NOT due to age or environment as a sporadic result. They are due to genetic mutations that have been inherited over time thru generations.
Also, you do not get part of a dwarf gene and therefore are less of a dwarf. It is all there or not. And if you are a dwarf you have two copies of the recessive dwarf gene, not some of the gene but all of it. What does occur is Penetrance and Expressivity. These genetic terms explain how dominant and recessive genes interact within an individual. What you might think is a minimal dwarf is actuallty a heterozygote mini just the dominant normal gene is being "overpowered" by the recessive dwarf gene. These are kind of hard to explain without visuals so try to think about it.
In my opinion, it would be very foolish of our breed and any Miniature horse registry to demand culling of all carriers, we should look at other breeds of animals and how they have dealt with genetic problems and how it was managed out, rather than go heck bent on instant cull and get it over with so to speak. You could destroy more good than bad and more people's livelihoods than you realize. For some unknown reason AMHA has been notorious for trying to reinvent the wheel on numerous things that other horse breeds have worked out and we for some reason do not use the learning curve to our advantage.
I definitely suggest it should at some point be required of all newly registered and other already registered horses that breed at least. Maybe in the way we have worked in the DNA typing requirement. I also think it should be required on the papers and required by all breeders to have some sort of education offered by the Assoc. to teach members how to breed these diseases out.
It was mentioned about other horse breeds use not so desirables for other purposes, like dressage or hunter, jumper, etc., well we do not have an entire separate multimillion dollar industry to send our undesirables to, like the Thoroughbreds and others do, we have to do it within our own industry, this is not ideal, nor is it going to work long term for those horse's values. That is why carriers should be used cautiously and with great care in how and who they are bred to. Therefore minimizing the chances of a dwarf. But also remember as someone wrote , these horses are property and anyone can breed however they want, no matter what. That is part of the reason we are dealing with these issues now, because of our forefather "breeders" weren't performing proper animal husbandtry skills but just reproducing whatever could reproduce. Anyone should have their choice to breed carriers or not to breed the carriers, but I do not think I have the right to tell someone else what to do with their horses, only a registry can do that. So we need to look at presidence.
I hope everyone does know that there is NOT a test yet, there may never be, but if there is one or many, I for one would test all of mine and would keep the carriers that are overall very good examples of the breed, I would just cross them accordingly. I would advertize my non-carriers and carriers if for sale, and I would by carriers if they were really good examples of the breed. I will be looking to buy those that are good horses and are carriers because some people will be dumping them cheap because they are carriers.
Remember, there is just a much chance (25%) of producing a homozygous normal horse from two carriers as there is to produce a dwarf (25%). This homozygous normal will NEVER EVER pass on a dwarf gene.
Chew on that awhile.
I hope I have not given the wrong impression to anyone, I care greatly for the well being of these horses, but we need to look ourselves in the mirror and honestly ask "am I working for the betterment of the breed ?", and look at other horse breeds and how they answered that question, before we throw away some of the best horses the breed has ever produced.
John Eberth
