5, 6, 7-Panel Testing for Paint & Quarter Horses

Quarter Horses and Paint Horses are the most common breeds of American stock horses, making up nearly half of all horses in the United States. They are revered for their versatility, athleticism, and unmistakable appearances. However, like all breeds, they can carry genetic predispositions to certain health conditions. To safeguard the health and well-being of our beloved partners, many breeders and owners rely on genetic testing, particularly the panel testing that is required by the American Quarter Horse Association (AQHA) and the American Paint Horse Association (APHA) for stud registrations. This comprehensive guide will delve deeper into what 5, 6, and 7-panel testing entails and why these genetic panels are commonplace for breeders and owners of Quarter and Paint Horses.

What is 5-Panel, 6-Panel, and 7-Panel Testing?

5, 6, and 7-panel testing serves as a vital tool in genetic screening, focusing on five to seven specific genetic mutations that are known to be prevalent in Quarter Horses and Paint Horses due to their shared ancestry. These mutations have been linked to various health issues, ranging from metabolic disorders to immunodeficiencies. While these genetic testing panels are the current standard in evaluating Quarter and Paint horses for a select group of health conditions identified by their registries, there are also testing options available that can assess a horse’s DNA for a much broader range of genetic health conditions, as well as performance markers and color genes.

The Difference Between 5, 6, and 7-Panel Testing

5-panel testing was previously the gold star DNA panel used for American Quarter Horse Association stallion registration. The 5-panel test evaluated a horse for HYPP, HERDA, GBED, MH, and PSSM1 - keep reading to learn about these acronyms and what they mean! That was until 2023 when a sixth test for Myosin-Heavy Chain Myopathy (MYHM) was added due to its prevalence and impact on the population.

The American Paint Horse Association has required a 6-panel test since adopting DNA health testing. The 6-panel test evaluates a horse for each of the genetic conditions included in the 5-panel test as mentioned above, as well as a sixth test for Lethal White Overo (LWO), sometimes referred to as Overo Lethal White Syndrome (OLWS). LWO is a genetic condition most commonly associated with Paint horses because it is related to white spotting in a horse’s coat which Paints are known for. However, it is important to note that LWO has been found in other breeds of horses including Quarter Horses, Thoroughbreds, and Miniature Horses.

A 7-panel test is a combination of the AQHA and APHA 6-panel tests. The 7-panel test evaluates a horse for five core health conditions, plus MYHM and LWO, for a more comprehensive look into a stock horse’s genes that can influence their health and the health of their potential offspring.

It is important to note that each of these panels is purely evaluating a horse’s DNA for the presence or absence of certain genetic health conditions, therefore they do not include any genetic color or parentage testing that may be required for registration.

The Importance of 7-Panel Testing for Quarter and Paint Horses

Selective Breeding Practices: Responsible breeding practices are essential for maintaining the health and integrity of Quarter and Paint Horse breeds, which includes minimizing the number of foals lost due to lethal genetic conditions. 7-panel testing aids breeders in identifying horses that are carriers of these commonly known conditions and selecting mating pairs wisely to minimize the risk of producing offspring with inherited disorders. Through selective breeding, breeders can gradually reduce the prevalence of these genetic mutations within the population, promoting overall breed health and reducing fatalities.

Health Management: By understanding the genetic status of their horses, owners can implement proactive measures to manage their health effectively. Horses identified as carriers of certain mutations, such as Polysaccharide Storage Myopathy Type 1 (PSSM1), can receive specialized care and monitoring to prevent the onset of associated health issues, ensuring a higher quality of life.

Ethical Considerations: Ensuring the health and well-being of horses is not only a matter of responsible equine ownership but also an ethical obligation. By conducting 7-panel testing, breeders and owners demonstrate their commitment to promoting the welfare of Quarter and Paint Horses, safeguarding them from unnecessary suffering, and ensuring a sustainable future for these beloved breeds.

What Does the 7-Panel Test Screen For?

The 7-panel test is a genetic screening tool that targets seven specific genetic mutations known to affect Quarter Horses and Paint Horses. Each of these mutations is associated with a particular disorder or condition that can impact the health and well-being of the horse. Let's explore what these panels test for:

Hyperkalemic Periodic Paralysis (HYPP): Hyperkalemic Periodic Paralysis (HYPP) is a hereditary muscle disorder prevalent in descendants of the Quarter Horse stallion, Impressive. It is a dominant genetic disorder resulting from defects in sodium channels in the muscle. Affected animals experience episodes of muscular weakness or tremors, which can lead to paralysis, collapse, and even sudden death. Heterozygous horses (HYPP/n) experience more moderate symptoms that can usually be managed through diet and exercise. However, homozygous horses (HYPP/HYPP) are much more severely affected, and some breed registries will not accept these animals.

Glycogen Branching Enzyme Deficiency (GBED): Glycogen branching enzyme deficiency (GBED) is a lethal recessive disorder that affects the horse's ability to store and utilize glycogen, a vital source of energy. Foals born with GBED typically exhibit signs of muscle weakness, seizures, respiratory failure, and may suffer from sudden collapse or death. Many affected foals do not make it full term and are aborted or stillborn. Carriers (gbed/n) have no known issues. Studies have indicated that between 4-11% of registered American Quarter Horses and American Paint Horses carry the GBED mutation.

Hereditary Equine Regional Dermal Asthenia (HERDA): Hereditary equine regional dermal asthenia (HERDA) is a degenerative skin disease that primarily affects the American Quarter Horse breed. Loose skin is often an early indication of the disease, and severe seromas, hematomas, and ulcerations usually develop around 1.5 years of age and progressively worsen. Horses affected by HERDA often face significant challenges in performing basic activities and are prone to skin injuries. There is no cure, and the majority of affected animals have to be euthanized within 2-4 years. This disease follows an autosomal recessive mode of inheritance, so for a foal to be affected, both the sire and the dam must carry the allele. This also means that horses can appear normal but be carriers for the condition. If two carrier horses mate, there is a 25% chance that the foal will have HERDA. Studies estimate that ~3.5% of Quarter Horses are carriers. It's recommended that both carriers and clinically affected horses with HERDA be removed from breeding programs.

Malignant Hyperthermia (MH): Malignant hyperthermia (MH) is a muscle disorder in which anesthesia, stress, or extreme exercise can trigger a hyperthermic state. Symptoms include high temperature, increased heart rate, high blood pressure, sweating, acidosis, and muscle rigidity. If symptoms are not immediately resolved, death is likely to occur. As this condition is autosomal dominant, even horses with a single allele (MH/n) exhibit symptoms. One study has shown that horses with at least one copy of both MH and polysaccharide storage myopathy (PSSM) variants have more severe clinical symptoms.

Polysaccharide Storage Myopathy Type 1 (PSSM1): Polysaccharide Storage Myopathy (PSSM) is a muscle disorder characterized by abnormal glycogen storage in muscle cells, leading to episodes of muscle stiffness, pain, and exercise intolerance, as well as chronic episodes of exertional rhabdomyolysis (“tying-up”). Acute symptoms are an unwillingness to move and muscle damage following exercise. Horses with PSSM1 often struggle with performing strenuous activities and may require specialized management strategies to alleviate symptoms. Heterozygous horses (PSSM1/n) experience more moderate symptoms that can usually be managed through a low-sugar/starch diet and exercise. However, homozygous horses (PSSM1/PSSM1) are generally more severely affected and are thus harder to manage. Additionally, one study has found that horses with PSSM1 and malignant hyperthermia (MH) exhibit more severe clinical symptoms.

Myosin-Heavy Chain Myopathy (MYHM): Myosin-Heavy Chain Myopathy (MYHM) is a genetic muscle disease found most commonly in stock-type horses that can result in two different presentations, Immune-Mediated Myositis (IMM) and Nonexertional Rhabdomyolysis “tying up,” which are both characterized by muscle damage or loss. Both presentations are associated with the same genetic variant. Horses with an MYHM variant may exhibit one or both presentations at different times in their lives, although some horses carrying the variant might not display any symptoms at all.

Lethal White Overo (LWO): Lethal White Overo (LWO), also known as Overo Lethal White Syndrome (OLWS), is a gene variant that produces a white spotting pattern. LWO is a genetic condition primarily found in Paint Horses with overo coloring patterns, as the name implies, however, it has been found in related breeds such as the Quarter Horse. It is an example of incomplete dominance, as horses that inherit one copy have a different phenotype than horses with two copies. Heterozygous horses (LWO/n) tend to have patches of white bordered (“framed”) by normal pigmentation, usually with blue eyes. In the typical expression, white patterning generally does not cross the topline. Homozygous horses (LWO/LWO) are born completely white and with megacolon, which leads to severe digestive abnormalities and necessitates immediate euthanasia on humane grounds. Some heterozygous horses do not have an obvious white spotting pattern but still can produce lethal white foals. Crossing two LWO/n horses has a 25% chance of producing LWO/LWO. Thus, it’s recommended to test even solid horses before breeding if there is any chance they could carry lethal white overo.

How Does 7-Panel Testing Work?

All three testing panels require a DNA sample to be collected from the horse, that is most commonly obtained from a mane or tail hair sample. The hair is pulled out by the root, where the DNA is found. This sample is analyzed in an International Society for Animal Genetics (ISAG)-approved laboratory, such as Etalon Equine Genetics, to identify the presence or absence of specific genetic mutations associated with the seven targeted disorders. Results are then provided to the owner or breeder, offering valuable insights into the horse's genetic health profile and guiding future breeding and management decisions. These results can also be directly shared with the appropriate registry.

Conclusion

In conclusion, 5, 6, and 7-panel testing serve as a cornerstone in the health management and breeding practices of Quarter and Paint Horses. By identifying potential genetic disorders and carrier horses, breeders and owners can make informed decisions that promote these iconic breeds' long-term health and well-being. Through responsible breeding practices, proactive health management, and ethical considerations, we can ensure a bright and healthy future for Quarter and Paint Horses for generations to come.

References

American Paint Horse Association. "Genetic Testing." https://apha.com/breed/geneticeq/

American Quarter Horse Association. "Genetic Testing." https://www.aqha.com/genetic-testing