Genetic Health Testing for Mustangs

If you ask any equestrian to describe the Mustang breed, there is no doubt the word “hardy” would be mentioned! We know them as an American symbol of freedom, adaptability, and resilience. As a feral horse, the Mustang is one of the few horse breeds across the globe that has long evaded human intervention when it comes to selective breeding. On one hand, this has allowed them to reproduce based on survival of the fittest, however, it has not completely protected them from developing certain genetic health conditions and risks. Some of the more common health conditions and risks we see in Mustangs include:

Polysaccharide Storage Myopathy Type 1 (PSSM1)

PSSM1 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 including targeted nutrition and exercise. It has been found in multiple breeds of horses, including Mustangs. 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. One study has also found that horses with PSSM1 and malignant hyperthermia (MH) exhibit more severe clinical symptoms.

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 and Mustang. 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.

West Nile Virus Risk (WNVR)

West Nile Virus (WNV) is a potentially severe viral infection transmitted by mosquitoes, and some Mustangs may have a genetic predisposition for a higher susceptibility to developing severe WNV symptoms. WNV primarily affects the central nervous system, causing symptoms such as fever, ataxia (lack of coordination), and muscle weakness. In severe cases, it can lead to encephalitis, which is an acute inflammation of the brain, or even death. Researchers have identified genetic markers associated with an increased risk of severe WNV symptoms in horses. Horses with one copy of these genetic markers (WNVR/n) may show milder symptoms, which can be managed with supportive care and preventative vaccination. However, horses with two copies of the markers (WNVR/WNVR) may experience more severe symptoms, making it crucial to implement preventive measures, such as vaccination and aggressive mosquito control, to protect these at-risk horses. This is a genetic health risk, meaning if your horse carries one or two copies of the variant, they are not necessarily destined to develop the disease. However, it does indicate that they are at a higher risk of developing more severe symptoms of WNV should they contract it.

Determining your Mustang's unique genetic health risks and conditions is crucial for their proper management and well-being, regardless of your breeding plans. Etalon’s premier Health Panel test helps you know your Mustang down to their DNA, revealing any potential health conditions or risks that we mentioned here, and much more. By identifying genetic health conditions and risks early on, you can make proactive decisions to help keep your Mustang happy and healthy for the long run.