Texas A&M Researchers Help Preserve History Through Equine Genetics Study

From the stunning rock formations to the fields of wild flowers, the Theodore Roosevelt National Park in North Dakota offers more than 70,000 acres of adventure. The park is also home to some of the most majestic and breathtaking animals in the United States—wild horses.

“Legend has it that the Teddy Roosevelt horses are descendants of the horses that were used by Sitting Bull and the Sioux tribe to defeat Lt. Col. George Custer at the Battle of the Little Big Horn,” said Gus Cothran, a clinical professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences (CVM). “But the known history of the herd suggests that only some of the Sioux horses had been in the park area at one time. Probably little, if any, genetics of the Sioux horses remain in the horses of the Teddy Roosevelt Park today.”

Cothran, who works in the animal genetics laboratory at the CVM, recently published a study in PLOS One that explored the Teddy Roosevelt horses’ genetic history to determine the possible origins of the herd.

“The genetics agreed that the herd was probably of diverse origin,” Cothran said. “This happens through horses being removed and other horses being introduced to the herd.”

Although their genes may have outgrown the legend, the Teddy Roosevelt horses are still a piece of living history. In fact, feral horses have existed in the park area since the mid-1800s.

However, efforts to preserve feral horses didn’t begin until the 1950s. These preservation efforts still continue today and researchers at Texas A&M such as Cothran are proudly a part of this movement.

Genetic diversity: Going, going, gone?

In addition to exploring the genetic history of the Teddy Roosevelt horses, Cothran’s study also analyzed the horses’ genetic diversity. Genetic diversity refers to the amount of genetic characteristics in a species’ genetic makeup that differs among individuals. Species with more genetic characteristics, or genetic diversity, tend to survive and thrive in their environment better than species with less genetic diversity.

Unfortunately, Cothran and his team of researchers found that the Teddy Roosevelt horses’ genetic diversity was limited.

“Limited genetic diversity means that all of the individuals within the population are very similar to each other,” Cothran said. “This can lead to inbreeding depression, which basically means that a large proportion of the population is carrying deleterious recessive variants of genes, or genes that will decrease the animal’s ability to survive in its environment.”

Luckily, Cothran and his research team found no evidence that the horses of the Theodore Roosevelt National Park are currently in danger of inbreeding depression. However, Cothran said, “They’re at a level of genetic variability that should raise concern. Their genetic variability is low enough that the possibility of an inbreeding effect is real.”

After publishing their study in 2018, Cothran and his research team released a statement about adaptive management practices that could help increase genetic diversity within the herd. These practices would be carried out by the National Park Service and potentially include introducing new horses to the herd while still keeping the population low enough for the environment to sustain them.

It takes a herd to save one

The study was initiated by Blake McCann, a trained population geneticist at the National Park Service. McCann and Cothran began working together several years ago when McCann sent Cothran almost 200 hair samples from horses within the herd.

Cothran, who has been researching wild horse genetics since the 1990s, began collaborating with Igor Ovchinnikov, who had also done genetic testing on this herd of horses through McCann.

Along with several other researchers at Texas A&M, Cothran and Ovchinnikov analyzed the horse samples for both mitochondrial genetic diversity (genes passed on to offspring from the mother only) and nuclear genetic diversity (genes that are passed on to offspring from both parents).

“This study was significant because it was the first time that a feral horse population had been comprehensively analyzed for both mitochondrial and nuclear genetic diversity,” Cothran said. “The study confirmed that the herd has low genetic diversity, which should be taken into consideration in future herd management.”

After all, who wouldn’t want to help preserve a piece of living history?

To learn more about the horses of Theodore Roosevelt National Park, visit https://www.nps.gov/thro/learn/nature/feral-wild-horses.htm.