ESI Q and A Forums Home
 Search       Members   Calendar   Help   Home 
Search by username
Not logged in - Login | Register 

scientific studies on inbreeding
 Moderated by: DrDeb  
 New Topic   Reply   Print 
AuthorPost
Kuhaylan Heify
Member
 

Joined: Fri Jan 30th, 2015
Location:  
Posts: 85
Status:  Offline
 Posted: Fri Feb 19th, 2021 02:35 pm
 Quote  Reply 
Dear Dr. Deb.. I ran across a study of inbreeding in Germany of a closed herd of arabs. The study showed a ,' mean herd homozygosity,' of 52.33%.. Does anything over 50% mean that a given individual is more than a direct daughter or son of a given parent? Also, if 36 horses bred over a period of 35 years each carry over 52 percent of the same genes is a breeder not in effect breeding all brothers and sisters with each other- thus doing direct incestuous breeding. So it would appear that rotating outcrosses of breeding groups within a breed or crossbreeding would be the way to go..
best
Bruce Peek

DrDeb
Super Moderator
 

Joined: Fri Mar 30th, 2007
Location:  
Posts: 3298
Status:  Offline
 Posted: Sun Feb 21st, 2021 08:34 am
 Quote  Reply 
Yes, Bruce, that is what is going on. And yes, outcrossing at periodic intervals is absolutely necessary to prevent 'genetic load,' i.e. the buildup or rise in frequency in the population of very deleterious alleles. Such things as hydrocephalus, twisted snout syndrome, problems with nondevelopment of pelage, and a wide array of metabolic problems are what I mean.

Did you read the Quarter Horse articles in the horse breeding series in EQUUS Magazine? Those were in last year's issues and there the topic is discussed very thoroughly, particularly with reference to the Kleberg/King Ranch QH breeding program. You don't have to be interested in QH's to read this -- the principles discussed there apply everywhere, to all mammals and certainly to all breeds of horses -- Cheers -- Dr. Deb

Kuhaylan Heify
Member
 

Joined: Fri Jan 30th, 2015
Location:  
Posts: 85
Status:  Offline
 Posted: Sun Feb 21st, 2021 03:07 pm
 Quote  Reply 
Yes Dr. Deb I have your Equus quarter horse series as it is a handy reference guide. Also I ran across a couple of PBS videos on line in which domestication is discussed which mention that the Botai people are thought to have been the first ones to domesticate horses and that the Pzrezalsky( sp) were the first horses to be tamed and then after the Botais disappeared, reverted to wild status in central asia. Also they say that the horse genome essentially collapsed at about the time of domestication
and that the Y chromosome once came in a bunch of variants but was thought to have dwindled down to just one which resulted in researchers thinking that there is now only one Y chromosome spread species wide. However other studies abstracts I have looked at emphatically state that they can tell the difference nowadays between Iberian Ys, Thoroughbred Ys, and Arab Ys. The studies also state that they were able to determine that there has been recent outcrossing in track racing Arabs to Thoroughbreds, because they found the Byerly Turk Y in samples of several Arab Track
racers.
best
Bruce Peek

DrDeb
Super Moderator
 

Joined: Fri Mar 30th, 2007
Location:  
Posts: 3298
Status:  Offline
 Posted: Mon Feb 22nd, 2021 09:57 am
 Quote  Reply 
Bruce, this is all very interesting, but what was your actual question?

Kuhaylan Heify
Member
 

Joined: Fri Jan 30th, 2015
Location:  
Posts: 85
Status:  Offline
 Posted: Mon Feb 22nd, 2021 02:10 pm
 Quote  Reply 
ok, Is it really true that there is only one Y chromosome? And or, has enough genomic decoding been done so that scientists can really tell the difference between Iberian, Thoroughbred, and Arab Ys?.. As I understand it most Warmblood breeds have Thoroughbred Ys. Do you know if that is the case, or if the Warmbloods have remnant native ,' Mossback y chromosomes?
The one Y chromosome theory would dovetail with the idea that there has been a massive collapse in genetic diversity among horses as a species and that the single extant Y lent itself to trainability..Also is it true that the first people to domesticate horses the Botai disappeared without a trace, save for a couple percent genetic contribution to neighboring peoples. If so why did they disappear what was the cause, Could it have been plague? It is known that sucessor peoples did suffer from plague so maybe pasturella pestis wiped out the Botais as they were an early people and might not have had time to work out folkways needed to minimise contact with ground dwelling rodents thought to be the vector species for plague..
Finally should breeders make multi generational efforts to as radically as possible outcross what ever breeds they have to reshuffle their genetic cards?
best
Bruce Peek

DrDeb
Super Moderator
 

Joined: Fri Mar 30th, 2007
Location:  
Posts: 3298
Status:  Offline
 Posted: Mon Feb 22nd, 2021 04:16 pm
 Quote  Reply 
Bruce, you are asking me to criticize literature which has already been professionally vetted. The process of publishing scientific results involves a review process which is called "jurying", and all professional journals are not merely edited, but also juried. For example, I and my colleague Bob Timm at K.U. currently have a paper submitted to the professional journal "Archaeofauna" which is at the moment -- as the first step in the publishing process -- out for review by a "blind" panel of three reviewers chosen by the editor. It is "blind" because the authors do not get to know who the reviewers who constitute the "jury" are. They are selected by the editor because he knows them to be highly qualified peers working in the same area of expertise.

So what you are asking me to do is verify what has already been verified. If you read about the Botai people in a newspaper or in a popular magazine like "Psychology Today" or "Smithsonian", you were reading an article prepared by a reporter who had read the original report published in a professional, juried journal. For the content not to be true, then, either the reporter got his facts wrong, or else the original jury was wrong.

But neither you nor I are in any position to criticize the jury, are we. So I take the reports about the Botai people to be true and accurate, until I see a report in a juried journal which presents contrary arguments.

I am in possession of the original, juried and professionally published reports concerning the Botai. However, I am not at all familiar with what you are saying about 'Y' chromosomes, so I have to ask you to provide me with either .pdf copies of the professional literature -- or else the popular newspaper or magazine article that you read. It is normal for the reporter to cite the professional reports that he read in order to prepare his piece and those citations will appear either in the text of the popular article, or compiled at the end. I say this for your benefit, because if you're interested to that degree, you can then search Google Scholar to see whether you can obtain the original, professionally juried reports. But I repeat, you will have to send me either .pdf's of the relevant articles or else at least provide me with the citations so that I can get them myself.

As to plague and all that, Bruce, that's pure speculation on your part and I am, again, in no position to comment. -- Dr. Deb

ilam
Member
 

Joined: Sat Apr 30th, 2011
Location: Texas USA
Posts: 60
Status:  Offline
 Posted: Thu Apr 29th, 2021 05:59 pm
 Quote  Reply 
I remember reading a while back that they found proof of TB interbreeding in racing-bred Arabs. I just found this citation:

Cosgrove EJ, Sadeghi R, Schlamp F, Holl HM, Moradi-Shahrbabak M, Miraei-Ashtiani SR, Abdalla S, Shykind B, Troedsson M, Stefaniuk-Szmukier M, Prabhu A, Bucca S, Bugno-Poniewierska M, Wallner B, Malek J, Miller DC, Clark AG, Antczak DF, Brooks SA.
Genome Diversity and the Origin of the Arabian Horse. Sci Rep. 2020 Jun 16;10(1):9702. doi: 10.1038/s41598-020-66232-1. PMID: 32546689; PMCID: PMC7298027.

Abstract:
The Arabian horse, one of the world's oldest breeds of any domesticated animal, is characterized by natural beauty, graceful movement, athletic endurance, and, as a result of its development in the arid Middle East, the ability to thrive in a hot, dry environment. Here we studied 378 Arabian horses from 12 countries using equine single nucleotide polymorphism (SNP) arrays and whole-genome re-sequencing to examine hypotheses about genomic diversity, population structure, and the relationship of the Arabian to other horse breeds. We identified a high degree of genetic variation and complex ancestry in Arabian horses from the Middle East region. Also, contrary to popular belief, we could detect no significant genomic contribution of the Arabian breed to the Thoroughbred racehorse, including Y chromosome ancestry. However, we found strong evidence for recent interbreeding of Thoroughbreds with Arabians used for flat-racing competitions. Genetic signatures suggestive of selective sweeps across the Arabian breed contain candidate genes for combating oxidative damage during exercise, and within the "Straight Egyptian" subgroup, for facial morphology. Overall, our data support an origin of the Arabian horse in the Middle East, no evidence for reduced global genetic diversity across the breed, and unique genetic adaptations for both physiology and conformation.

Isabel

Last edited on Thu Apr 29th, 2021 06:00 pm by ilam

Kuhaylan Heify
Member
 

Joined: Fri Jan 30th, 2015
Location:  
Posts: 85
Status:  Offline
 Posted: Thu Apr 29th, 2021 09:28 pm
 Quote  Reply 
Isabel: The other interesting thing about the 378 study was that it was surmised that the reason why so many genetic illnesses are showing up is the extent of inbreeding that is going on. They included some color coded scatter plots which clustered straight egyptians and some american al khamsa horses in concentrated areas.. It was also found that the cradle country horses still had a ton more genetic diversity. The authors attributed this to the rather small amount of horses exported from the middle east to the western hemisphere and then bred within their own lines without consistent access to a stream of new horses from the middle east. Gus Cothrans did a review of the Polish arabs since WW2 and found just over 30%( if if remember correctly) of genetic repitition in recent years compared to o% when the review period began starting in 1948. So founder effect has been multiplied and multiplied in the Polish horses too- though not to the extent of the straight egyptians.
best
Bruce Peek

DrDeb
Super Moderator
 

Joined: Fri Mar 30th, 2007
Location:  
Posts: 3298
Status:  Offline
 Posted: Sat May 1st, 2021 09:12 pm
 Quote  Reply 
Isabel, thank you for sending an actual citation. As I said above, accusing the Arabian racing industry of cheating (i.e. by crossing with Thoroughbreds) is fairly serious business and one would not be justified in doing it without some definite evidence. But now that I see the evidence, then we have reason for believing it -- no longer just a rumor, in other words.

At the same time, I wonder how much this really matters. Registry qualifications for Arabians have been heavily influenced by the personal preferences and beliefs of some of the larger and more politically powerful breeders. So for example, the Russian imports from Tersk, which were widely thought to be at least somewhat intercrossed with TB's, were admitted to the American registry and that set off a whole boom in Russian breds who were the cat's whiskers at all the shows in the 1980's and early 1990's. At the same time, when the King of Jordan sent some stallions that had absolutely passed muster by the best and most knowledgeable pedigree reviewers (i.e., Pesi Gazder and the World Arabian Horse Organization) -- and I never saw more blueblooded Asil horses in all my life -- they were denied registry here, all got gelded and sold off cheap at auction when instead they could have founded dynasties of excellent horses.

So an American Arabian "is what it is", and that means in some cases it will be a crossbred somewhere back in the pedigree. Yet such animals have official papers and that's their entry ticket to Arabian shows. My view is -- if you want to play horse show, then be sure to get yourself a horse that has the ticket. If you just want a real good horse, then be sure you know how to tell one when you meet him, and then you buy him papers or not, and enjoy him for all the other gazillion things you can do with a horse other than go to horse shows. Cheers -- Dr. Deb


 Current time is 06:46 am




Powered by WowBB 1.7 - Copyright © 2003-2006 Aycan Gulez