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The Carter Mustang Mystique and Exciting mtDNA Results

Updated: Dec 16, 2021

Who Are These Horses and the Search for Identity

The first time you are fortunate enough to see a wild horse, it raises the hair on your arms, sends chills down your spine, freezes you dead in your tracks. It was an unexpected encounter with a small band. Quickly gone, running from the threat of my presence, until they were no more than specks on the horizon. They ran on long after the threat was behind them. They ran for the joy of it, for the freedom of it. For their


We were en route from Antelope Springs, heading for a quick looksee at Sulphur, an old mining operation long since turned ghost town close by the desert’s edge. And, once there, I would find Sulphur is just as Sulphur does. An ill-smelling flat, dusty spread of plain where it was too hot and still for even a hint of powdery particulate to hang in the air, there where uninspiring plain butted up against a red-gold infused hillside with a scraped-out bowl where sulphur could be extracted. But, that was for the future and I

wasn’t interested in thinking about that yet.

It was impossible to stop thinking about the horses. How incredibly hardy, these creatures, to run so far without being compelled in the heat of the day, and to survive where not much beyond sage brush and scant dry grass would grow, and in places where opportunity for water were few and far between. The horses were only there because nobody else wanted to be here, or these wild ones had just plain outlasted everyone else. Where did they come from? Where did they get their endurance, their

beauty, their intelligence, and their unflagging will to survive.

That was what I was thinking, all that I was thinking, back just after the turn of the last century, in July of two-thousand. I was a mere Johnny-Come-Lately to mustang spotting, retreading my way through questions countless others have asked through the passing of the centuries. But, now in our current era, we are finding out more and more about these questions every day. Thanks to science, we can delve deeper and deeper into the genetics of mustangs to understand their provenance. Amazing studies are even now bringing forward scientific evidence of the origins and migrations of even the very earliest ancestral horses of prehistory.

But for today, we have an announcement much closer to home. The results from our exciting testing program analyzing the DNA of the Carter Reservoir herd.

Samples from 31 Carter horses were sent to Certagen, a specialty lab in Germany with particular expertise in equine DNA. Certagen compares test samples from individual Carter Reservoir horses against a known pool of equine genetic material. This genetic material has been collected by scientists from well-known research groups such as the McDonald Institute for Archaeological Research, University of Cambridge, Institute for

Clinical Biochemistry and other such groups.

Data based on these genetics was used in a study identifying where and when horses were first domesticated.[1] This known pool of genetic material utilized mtDNA samples from 318 horses that included 25 Oriental and European breeds as well as American mustangs. These horses were unrelated with the samples provided by their breeders who could document the ancestry of each horse sampled, typically back for five generations. (American mustangs were also in the samples, but without breed pedigree info.)

The data the study team collected was augmented with previously published mtDNA sequences from GenBank or other publications. The combined data resulted in a total sample size of 652 horses, which was the largest dataset on this subject available at the time of the study.

The samples used in the study fell into 17 Phylogenetic Clusters (phylogenetic meaning physically alike individuals were combined in a cluster), and they further determined that some clusters aligned with particular breeds and/or geographic regions. The study’s 17 Cluster designations are widely recognized and used when referencing equine DNA testing results.

The 17 Clusters were compared to each other, and also with DNA data the team had for ancestral horse remains which had been found in permafrost by archaeologists.

In short, the pool of DNA data these scientists collected for their study “Mitochondrial DNA and the origins of the domestic horse”, were used to determine when and in what regions horses were originally domesticated, how breeds developed over time, and the geographic factors that played into the development of each of these clusters.

The DNA samples from the Carter Reservoir horses were compared with the DNA of all the horses in each of the study’s 17 Clusters at a genetic level. This data pool is extensive enough to definitively assess which of the clusters each Carter horse’s DNA most closely matches.

We are delighted to share that Certagen Lab has stated, “Our findings clearly indicates a Spanish origin of the ancestors of the mustangs, living in the Carter Reservoir.”

All 31 of the Carter horses tested fell into one of two clusters: D1 or D3. Both of these clusters roll up to the D Super Cluster identified with Andalusian/Lusitano/African Barb lineage. This is a heritage that is clearly Iberian. With 100% of the individuals tested demonstrating this outcome, the Carter herd shows genetically ancient Spanish-Iberian ancestry, directly tracing back 500 years to those horses brought to North America on the ships of the early Spanish explorers. The tests also support the Carter Reservoir herd may well have the highest percentage of Spanish-Iberian DNA of any U.S. wild herds tested to date, identifying the Carter herd as an irreplaceable Heritage type.

Tighten Up Your Stampede Strap! The Trail Continues!!

Carter Reservoir Mustangs, Inc. has ambitious plans to conduct further testing to explore the information that can be obtained about these horses from Nuclear DNA tests. Future results from this type of DNA testing will reveal individual familial relationships within the herd, providing critical insights into the structure of smaller family bands and groupings within the overall herd.

Moreover, testing results combined with information collected during extensive field work that has been done out on the range regularly, year in and year out, over more than a decade provide incredible insights into these wild horses. Data on the Carter Reservoir horses is being compiled into an archive including hundreds of pages of descriptive field notes along with more than 100,000 photographs.

This provides an unprecedented view into behaviors in the wild, conditions of the herd and the herd’s range over a wide span of time and seasonal changes, as well as ecosystem cycles. It can evidence behavioral and physical progression over many years revealing development in both individuals and the overall herd, which can be compared within and across family bands.

Best of all, this is labor of love and our invitation welcoming the world to learn and understand more about this very unique Carter Reservoir Mustang herd, and all mustangs everywhere.

[1] (PNAS August 6, 2002 vol. 99 no. 16 10905–10910; “Mitochondrial DNA and the origins of the domestic horse”; Thomas Jansen, Peter Forster, Marsha A. Levine, Hardy Oelke, Matthew Hurles, Colin Renfrew, Jurgen Webe, and Klaus Olek. Contributed by Colin Renfrew, 6/3/2002.)


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