The tantalizing possibility that the lineages of some free-roaming horses in America can be traced back to horses imported from eastern Asia and Russia have been raised in the findings of a study.
The study centered on analysis of maternal (mitochondrial) DNA from horses living wild in Theodore Roosevelt National Park, which lies in western North Dakota where the Great Plains meet the rugged Badlands.
University of North Dakota researcher Igor Ovchinnikov and his colleagues, writing in the journal PLOS ONE, said the free-roaming horses in the park represented an iconic era of the North Dakota Badlands.
“Their uncertain history raises management questions regarding origins, genetic diversity, and long-term genetic viability,” they said.
Hair samples with follicles were collected from 196 horses, a number which comprises nearly all the horses living in the park, and the mitochondrial DNA was analyzed.
Three mitochondrial DNA haplotypes (sets of genetic determinants) were found in the park horses, belonging to haplogroups L and B.
They sequenced one mitochondrial genome from each haplotype.
Two complete mitochondrial DNA sequences of haplogroup L were found to be closely related to the mitochondrial DNA of the American Paint horse.
However, haplotype B sparked considerably more interest. It did not have close matches in the GenBank, which an open-access, annotated collection of all publicly available genetic sequences.
Testing placed this sequence in a group consisting of two horses from China, one from Yakutia in Russia, and one from Italy, raising a possibility of historical transportation of horses from Siberia and East Asia to North America.
The researchers said four family groups (13.8%) with 31 animals fell into haplogroup B, with distinct differences to the two haplogroup L lineages identified.
The closest mitochondrial DNA sequence was found in a Thoroughbred racing horse from China, but its sequence was still distinct in several areas.
The testing also revealed links to the mitochondrial DNA of an Italian horse of unspecific breed, the Yunnan horse from China, and the Yakutia horse from central Siberia, Russia.
Haplogroup B seems to be most frequent in North America (23.1%), with lower frequencies in South America (12.68%) and the Middle East (10.94%) and Europe (9.38%).
“Although the frequency of this lineage is low (1.7%) in the Asian sample of 587 horses, this lineage was found in the Bronze Age horses from China and South Siberia.”
The unexpected link between lineage B in the park horses and those from Asia may be explained by insufficient sampling of horse mitochondrial genome variation in Europe and North America, the authors said.
“However, this observation leads to an exciting hypothesis about a link between Siberian-East Asian and part of North American horses and a new route of exporting horses to North America.”
They noted that the intriguing possibility of gene flow from Siberian horses of Yakutia to Canadian horses was suggested from the genetic variation observed in the wild horse population living in the remote Brittany Triangle region of British Columbia.
“To prove this link, extensive sampling of DNA for complete mitochondrial DNA sequencing and microsatellite profiling should be carried out from horses in Siberia (Russia) and China.
“To date,” they noted, “there is limited historic record that horses may have been transported to North America with Russian and Chinese explorers and merchants.”
Analysis showed that the park horses were distinctly different from 48 major horse breeds. However, their genetic diversity was below that observed for most other feral herds and domestic breeds, most likely due to a population bottleneck in the 1960s.
The researchers stressed that the existing genetic data sets of horses were insufficient to determine the exact origins of the park horses.
However, the results have highlighted the horses’ management needs.
“It is recommended that new genetic stock be introduced and that adaptive management principles are employed to ensure that unique mitochondrial lineages are preserved and genetic diversity is increased and maintained over time,” they said.
The study team said the horse herd at Theodore Roosevelt National Park may have originated from multiple sources. There were Native American horse trade centers nearby. Ranch horses were bought from the Native Americans, or in some cases confiscated, and it was common to free-range them in the badlands for breeding purposes.
From the mid-1880s onward, the fate of these particular animals and their lineage is unclear.
“Free-ranging of ranch horses was a common practice at this time, and horses of many breeds were propagated among local ranches, with influxes of available stock from the railroad and from cattle drives along the Great Western Cattle Trail. Thus, it is unclear to what extent tribal ponies contributed to local feral herds over time, but it is likely that free-ranging animals commingled.”
From the early 1900s until the establishment of the park in 1947, little is known about the status of feral horse herds in the area.
The park began managing horses in the 1960s, and in 1966 it was thought that only 16 animals remained. The herd was allowed to grow, with periodic roundups and auctions serving as the mechanism for maintaining horse numbers at a stocking rate appropriate for available forage.
In the 1980s several stallions (including an Arabian, a Shire/Paint cross, a Quarter Horse, and three horses from the Bureau of Land Management) were introduced in an effort to improve genetics, and it is thought that some trespass horses may have entered the herd over time, despite the park boundary being fenced since 1956.
The full study team comprised Igor Ovchinnikov, Taryn Dahms, Billie Herauf, Blake McCann, Rytis Juras, Caitlin Castaneda and Gus Cothran.
Ovchinnikov IV, Dahms T, Herauf B, McCann B, Juras R, Castaneda C, et al. (2018) Genetic diversity and origin of the feral horses in Theodore Roosevelt National Park. PLoS ONE 13(8): e0200795. https://doi.org/10.1371/journal.pone.0200795