The Promise of the Horse Genome Project

The Cornell component of the Horse Genome project, led by Doug Antczak, is currently undertaking mapping and characteri- zation of genes of the immune defense system. Results are used to develop new assays for immune function.

The Promise of the Horse Genome Project

Less than 10 years ago, horse geneticists from around the world agreed to work together toward a common goal: to map the horse genome. In a world that's usually very competitive, these researchers divvied up the job among their laboratories and came to the common understanding that they would share and integrate their data.

“We tried to parse the genome to a manageable size, and we've done it by breaking it down by chromosomes, of which there are 32 pairs in the horse,” says Douglas Antczak, VMD, PhD, director of the Baker Institute for Animal Health. “Although each horse chromosome has about 100 million bits of information, it only contains about 1,000 genes, so it's a manageable number.”

In 1995 only about 20 genes had been identified and mapped.

He goes on to explain: “If you think of a chromosome like an interstate highway, the linkage markers are like the exit signs. They're important for making our maps of the horse genome. There are over 500 mapped markers so far that indicate the order and placement of genes on chromosomes; they provide insights into which traits are inherited together. About 500 more are being characterized. We have mapped more than 300 genes on our physical map, with more being mapped weekly, and we've sequenced more than 3,000 genes, with more completed daily.”

The researchers have also developed a comparative map, which compares the organization of genes in the human and horse chromosomes. The strong similarity the horse genome has with the genomes of other animals—particularly humans, cattle, and pigs—has fast-forwarded much of the equine genomics work. The project also has generated a comprehensive map that integrates the information from the other maps to create a unified view of the organization, complexity, and diversity of the equine genome.

The goal of this group of some 120 scientists, from laboratories in 12 countries, is to fill in as many dots as possible on the equine gene map. New technologies have made mapping and sequencing easier, more efficient, and less expensive, so the finer details are getting filled in at an ever faster pace. The final portrait of the genome map of the horse will provide keys to unlocking information on the genetic underpinnings for all kinds of equine traits and genetic predispositions. This information has broad application in diagnostics, breeding, physiology, performance, and the prevention and treatment of disease.

Applications of the Equine Gene Maps

  Unlike most other scientific endeavors that don't have practical applications for decades after their initial work, the horse genome has already reaped benefits for equine scientists, clinicians, and horse breeders. Genetic tests are now commercially available for Severe Combined Immunodeficiency Disease (SCID) in Arabians, hyperkalemic periodic paralysis (HYPP) of quarter horses, and the Lethal White Syndrome in paint horses. But these genetics tests are just a peek at what's to come.

“Very rapid progress is expected in the coming years, and this progress holds promise to transform many aspects of equine medicine,” Antczak says. “By understanding how multiple genes act together to control certain traits, we think the horse genome will allow us to identify disease-causing genes and determine which genes produce characteristics that are valued by horsemen.

“Unraveling the horse genome will not only improve breeding and performance but will also be used for a wide range of applications. Among these are: developing better vaccines for infectious diseases (such as West Nile virus), preventing cancers with a genetic predisposition (such as equine sarcoid), and developing gene therapies to help horses get back to racing after they've been injured or become arthritic.”

Findings of the Horse Genome Project may lead to tests to diagnose diseases such as Chronic Obstructive Pulmonary Disease (COPD or heaves), wobbles, strangles, swayback, and other developmental bone and muscle diseases. They may also be used to identify the genetic code for traits ranging from coat color to muscle physiology. Also they may lead to strategies to prevent certain reproductive problems, such as Mare Reproductive Loss Syndrome. Too, genome data can be used to breed sounder horses by making it possible to screen stallions and mares for certain vulnerabilities such as bone and muscle weaknesses, allergies, exercise-induced pulmonary hemorrhage (“bleeding”), and other problems that prevent horses from performing at peak.

Researchers are already working on ways to identify the genes for a host of disorders, including cerebellar hypoplasia, megacolon disease, epitheliogenesis imperfecta, muscle diseases such as tying-up syndrome, and bone disorders.

“On a more global scale, there are the areas of nutritional genomics and physiological genomics of performance that can help us understand how to condition and train horses better so as to keep them sounder for longer,” Antczak adds. “All of these medical advances mean more economical breeding, training, and maintenance of horses.”

The equine gene maps also will be used in ways that are not closely tied to traditional genetic studies. Researchers can now test thousands of genes in a single experiment through the use of so-called “microarrays.”

“These arrays will find use in almost every aspect of equine medical research: from bone and joint physiology through immunology to reproduction. Rather than concentrating on a single gene of interest, gene array experiments allow us to monitor very large numbers of genes at the same time,” Antczak explains. “Such an approach can help determine how infectious agents affect many aspects of an animal's physiology—not only its immune system—and uncover unexpected activities of pharmacologic agents. For complex conditions that may be nonhereditary but involve gene expression (such as laminitis, developmental bone diseases, and colic), microarrays may hold the key to the development of new modalities of treatment through a more complete understanding of pathogenesis.”

Although the genome maps may be only a sketch now, researchers are filling in more details on a weekly, sometimes daily, basis. The promise of the Horse Genome Project for those who care for and love horses is staggering.

“Its use has already begun, and its widespread application awaits only our imaginations,” Antczak concludes.

The Horse Genome Project is linked to various web sites and two databases that hold the information on the equine genome. These web sites will be continually updated as more information on genome organization of the horse is made available.