And coming around the track, looking promising ... The horse genome map

Published on June 15, 2002
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Race Horse

In 1995, the map of the horse genome was in its infancy—researchers had mapped only seven genes to specific chromosomes. Today, researchers have mapped more than 900 genes. The progress, in large part, is the result of collaboration between various international laboratories.

"By 1995, map research was well along for other livestock species, but very little had been done for the horse," said Dr. Ernest Bailey, a researcher at the University of Kentucky's Maxwell H. Gluck Equine Research Center, one of the centers working on the map. "With the limited resources that each of our laboratories has, we figured the best thing to do was to collaborate."

And since the mid 1990s, that is exactly what various laboratories from around the world have done. Institutions work and are funded independently, but researchers share information. "If someone makes an advance, they can take advantage of it at another laboratory," said Dr. Nat White, assistant director of the Marion duPont Scott Equine Medical Center in Leesburg, Va.

One example is a collection of DNA samples that was obtained from 15 horse families and distributed to all collaborating laboratories. "We basically have been investigating the relationship of our markers with each other's markers, using the same family," Dr. Bailey said. "We want to know how they relate to what people are doing in other laboratories."

Twenty-two laboratories in 12 countries have contributed to the first-generation genome horse maps. Major research groups in the United States are located at the University of California-Davis, Cornell University, University of Kentucky, University of Minnesota, Texas A&M University, and Tufts University. Private laboratories also contribute. International groups include laboratories from Australia, New Zealand, France, Sweden, Germany, South Africa, Japan, Czech Republic, Poland, Denmark, Norway, and the United Kingdom.

The collaboration has been fruitful. In addition to 900 mapped genes, scientists have also made great strides in determining linkage maps that illustrate the order and placement of genes on a chromosome, characteristics that determine which traits are inherited together. More than 800 markers have been linkage mapped, an increase from just a handful in 1995.

According to Dr. Bailey, the current gene map has been used to identify several inherited traits in horses. It has also been fundamental in investigating many nonhereditary traits, especially gene expression relevant to complex diseases such as laminitis, developmental bone diseases, and colic.

According to Dr. Doug Antczak, director of the James A. Baker Institute for Animal Health at Cornell University, the benefits of genomic studies are already apparent. During the 1990s, scientists identified genes responsible for three important genetic horse diseases and developed tests, which are now commercially available. Breeders and prospective buyers can now test animals for severe combined immunodeficiency disease in Arabian horses, hyperkalemic periodic paralysis in Quarter Horses, and lethal white syndrome in Paint Horses. Scientists are currently using newly identified markers to seek out mutant genes that cause other autosomal recessive diseases.

Other researchers are working on identifying the genes for cerebellar hypoplasia, megacolon disease, epitheliogenesis imperfecta, muscle diseases such as tying-up syndrome, and bone disorders.

And genes for basic traits such as coat color are also getting attention. The gene for palomino color, for example, has been mapped. "Breeders want to know if a stallion is a homozygote for a particular trait," Dr. Bailey said.

Progress with the horse genome has been spurred on by genetic research in other animals. The size of the genome as well as the number, nature, and sequence of genes is strongly conserved among vertebrate species. "Genetic research is moving very fast," Dr. White said. "Now that the human genome and the mouse genome have been fully mapped, it's possible to look at genes in other animals, and using the template from the human or mouse, find similar genes."

Yearly meetings between the collaborators have been made possible by funding from the Dorothy Russell Havemeyer Foundation. The Department of Agriculture provides funds for centralized facilities and other special resources. The Harry M. Zweig Memorial Fund for Equine Research in New York State, and organizations such as the Morris Animal Foundation and the Grayson-Jockey Club Foundation have also made grants to individual scientists for basic genetic studies.


Researchers estimate that completing the horse genome map will cost between $7 million and $10 million. According to Dr. Bailey, substantial new funding is necessary to move the project forward.

"I would have thought, by now, that there would have been more interest from the horse industry in pursuing the work," he said. "For whatever reason, I don't think that genetics is given that much priority in horses, and I think that's a shame. It's expensive to do."

To spark interest from the equine industry, an unofficial group called the Equine Research Coordination Group—comprising the AAEP, AQHA, Grayson-Jockey Club Research Foundation, and the Morris Animal Foundation—sponsored a meeting this past March to explore the benefits of equine genome research.

After the meeting, the group suggested that the researchers develop a proposal about what to fund, and this was submitted to the unofficial equine group soon afterward. David Foley, executive director of the American Association of Equine Practitioners, says the four meeting funders will most likely discuss the proposal at the AAEP annual convention in December.

Currently, no one centralized organization can allocate the amount of funds needed to finish the map, according to Dr. White. The USDA provides only minimal support for equine research. "We have a need to increase both awareness as well as raise the amount of money needed to complete today's highly technical research," he said.

Dr. White hopes the March meeting will help change the tide. "The equine industry is just beginning to understand what genomic research can offer for solving equine disease problems," he said. "I think each of the research foundations will now [pay] closer attention to genomic research and the potential for funding grants on this topic."