By Amy Young, UC Davis Center for Equine Health

1. DNA is found in the nucleus of cells. Samples submitted for genetic testing are usually hair, blood, or tissue. Hair samples must contain the “bulb,” which looks like a tiny ball at the root of the hair. This is where the DNA is located. When submitting hair samples, make sure to pull, not cut, the hairs so the bulb is present. Blood and tissue samples require additional steps, such as an anticoagulant (for blood) or freezing (for tissues). Always follow the testing laboratory’s instructions for sample submission and contact them with questions.

2. There is no age limit for DNA testing. An animal’s DNA profile does not change over time, so a horse can be reliably tested at any age. Genetic tests can be performed for foals, but it is recommended to submit 30 to 50 tail hairs since the bulbs on foal hair are smaller than adults and more are needed.

Photo Courtesy of UC Davis

3. Parentage testing is based on exclusion. The offspring, dam, and potential sires are tested for a number of markers, and the offspring is compared to the potential parents for each marker. The offspring must have received one allele for each marker from each parent. It is possible to do parentage testing with a sample from only one parent (about 95 percent accurate), but results are more accurate (greater than 99 percent) with both. Accuracy will decrease when the potential parents are part of a large group of closely related animals.

4. SynchroGait™ tests for a genetic variant that facilitates lateral gaits (ambling and pace). Owners can use this test to identify the natural ability of young horses for gait performance and use the results to make training decisions. Breeders can use the test to select for or against this mutation, depending on what is desirable in their chosen discipline.

5. Horses have three base coat colours that are controlled by the interaction of two genes. The coat colours chestnut, bay, and palomino are determined by horses’ genotypes at the MC1R gene (extension (E) locus), which controls the production of red and black pigment, and the ASIP gene (agouti (A) locus), which controls the distribution of black pigment to the mane, tail, lower legs, and ear rims (points), or uniformly over the body.

6. Dilution factors modify base coat colours. These include cream, champagne, dun, pearl, silver, and mushroom. The resulting coat colour depends on the combination of the base colour genotype and the dilution factor genotype. For example, a horse with one copy of the cream allele on a chestnut base colour will be palomino whereas on a bay base colour it will be buckskin. Modes of inheritance and causative mutations have been identified for these dilution factors, and genetic testing is available. 

Photo: Shutterstock/Rita Kochmarjova

7. Horse size is highly heritable. Height in horses is determined by the interaction of genetic and environmental factors (such as nutrition). Four genetic variants have been identified that account for more than 80 percent of horse height. One variant has a particular influence on height in warmbloods and a different variant has a strong influence on height in Shetland ponies and Miniature horses. Mutations related to dwarfism have also been identified in some breeds (dwarfism in Friesians, skeletal atavism or the reappearance of an ancestral genetic trait in Shetland ponies and American Miniature horses). Additional unidentified genetic variants that influence height in horses are likely.

8. Equine genetic ancestry tests are available, but there are a few things to keep in mind. Equine ancestry tests, or “breed prediction” tests, compare a horse’s DNA to horses in a reference panel. Results are dependent upon the breeds and number of horses of each breed in that panel (which can vary by test provider). Some horse breeds are not very genetically distinct from one another, and many breeds have influenced the creation of other breeds, which can complicate results. These tests can report the probability that a certain breed is an ancestral breed for a horse, but not the proportion or percent of that breed in a horse’s genetic makeup. The larger the number of breeds involved in a cross, the lower the probability of a clear result.

9. Genetic testing can be performed for embryos. Embryos recovered from uterine flushes as part of embryo transfer procedures can be tested to determine gender and genetic traits prior to implantation in the recipient uterus. This allows for selection of embryos that have the desired sex, coat colour variants, or that are free of known genetic diseases.

10. In the future, whole genome sequencing of individual horses will be more accessible. Whole genome sequencing of modern and ancient horses has provided a wealth of information to researchers. As this technology becomes more affordable (current cost is about $1600 USD per animal), whole genome sequencing of individual horses is likely to become more accessible. Coupled with advanced knowledge in equine health, whole genome sequencing will provide veterinarians, owners, and breeders with a powerful tool to tailor training, management, and health care to the individual animal.

Related: Research Advances Lead to New Genetic Tests for Horses

Related: AQHA's Dedication to Research and Success of the Five-Panel Test

Printed with the kind permission of the UC Davis Center for Equine Health. The UC Davis Center for Equine Health is dedicated to advancing the health, welfare, performance and veterinary care of horses through research, education and public service.