Comparative Orthopaedic Research Laboratory

Equine Genetic Testing

Genetic testing for degenerative suspensory ligament desmitis in the Peruvian Horse

We are now able to undertake genetic testing for risk of degenerative suspensory ligament desmitis in Peruvian Horses. Briefly:

  • Degenerative suspensory ligament desmitis (DSLD) in horses is a painful, debilitating disease resulting in a chronic severe lameness. Since there is no cure, euthanasia is often the outcome.
  • DSLD affects several breeds of horse including the Peruvian Horse
  • Using DNA from a blood sample or hair bulb sample, we can now predict whether your Peruvian Horse is at high risk of DSLD
  • We can determine genetic risk, meaning that even if a horse is at high risk for DSLD, there may be treatments that can help mitigate clinical risk

Why test your Peruvian Horse?

  • Working horses: There is no effective treatment for this disease. Management is palliative and is undertaken to manage suspensory ligament injury and tissue inflammation. Knowing that your horse is at high risk for DSLD will enable you to work with your veterinarian to help minimize risk and monitor for progressive suspensory ligament injury.
  • Breeding horses: DSLD is a heritable disease. Understanding risk of disease development in breeding horses should be considered in breeding decisions. Screening for genetic risk of DSLD can help minimize disease risk in the breed.
  • Foals: Individuals looking to purchase a young horse, particularly a horse intended for athletic work, can request or order testing to help minimize the risk that their new horse will develop DSLD.

How much will this cost?

  • Testing is expected to cost ~$330 per horse

Why does this cost more than other genetic tests available for horses?

  • Most other genetic screening currently available in the horse tests for simple Mendelian recessive or dominant diseases, meaning the test looks for a single mutation in a single location in a horse’s DNA code to say whether a horse has a disease-causing genetic mutation or not. These diseases are typically rare conditions.
  • DSLD is a complex disease in the Peruvian Horse. Complex diseases have both genetic and environmental factors that contribute to risk where the genetic contribution is defined by the heritability of the disease. This is one of the first genetic tests for a complex disease in horses, which means instead of checking just one part of a horse’s DNA, we need to evaluate many genetic markers across the genome and analyze the results using bioinformatics to predict disease risk for each horse.

What will the results mean?

  • Our test is accurate, and owners will receive a report categorizing their horse’s risk.
      • Predicted to be a case: A horse found to have marker genotypes that predict it to be a case is very likely to experience DSLD in their lifetime. However, environmental intervention may help prevent this from occurring.
      • Predicted to be a control: Horses found to have marker genotypes that are protective from DSLD are unlikely to develop suspensory ligament injury. However, this does not eliminate the possibility that they will develop DSLD if the horse has other environmental factors that can contribute to disease development.
  • DSLD has both genetic and environmental risk factors. For horses predicted to develop disease, early interventional changes in lifestyle may be able to help minimize overall risk for disease development.

Learn more here!

Background: the suspensory ligament

     DSLD and rupture of the suspensory ligament has many shared features with human tendinopathy, particularly Achilles tendinopathy in the ankle. What many people don’t appreciate is that the risk of people injuring their Achilles tendon is also influenced by genetics. In horses, the role genetics plays in risk of DSLD in certain breeds is better defined than in people.

        DSLD is a disabling equine disease with higher prevalence in specific breeds. Breeds with particularly high risk of DSLD include the Peruvian Horse, Paso Fino, Warmblood, and Akhal-Teke breeds amongst others. This disease is an important condition across the world and many horses are euthanatized because of this condition. DSLD is an acquired disease that usually develops by the age of 14 years in high-risk breeds. Many older horses experience disability because of DSLD.

Background: genetic testing

        Routine use of genetic testing for DSLD screening of horses from high-risk breeds would be a very valuable advance. Knowledge of whether individual horses had high or low genetic risk for developing DSLD would be valuable for selection of horses for breeding, pre-purchase examination of foals and young horses at the time of sale, and for personalized veterinary care of horses to mitigate risk of developing DSLD in horses have not yet developed suspensory ligament problems but have a predictive test indicating high genetic risk.

        Currently most genetic tests for the horse screen for simple diseases, meaning they look for a specific DNA mutation that results in a horse either having a disease or being a carrier for a disease, depending on whether the disease has a simple dominant or recessive mode of inheritance. Unfortunately, common diseases in horses, like DSLD, are complex diseases. A complex disease is the result of hundreds to thousands of genetic variants that occur through an animal’s genome, in addition to environmental risk factors. Until now, genetic testing for complex diseases in the horse has not been feasible.

Genetic contribution to degenerative suspensory ligament desmitis

        Our laboratory has focused on studying DSLD in the Peruvian Horse and the Akhal Teke. Over several years we have recruited many horses to our genome-wide association study (GWAS) project with community support. We have collected DNA on more than 200 Peruvian Horses that have all been closely screened for the presence or absence of DSLD. Using what is termed SNP (single nucleotide polymorphism) marker genotyping, we then looked at markers throughout the genome (DNA code) for each horse. This data set and the pedigrees collected from the families of affected Peruvian Horses has allowed us to accurately estimate heritability. In the Peruvian Horse, heritability of DSLD is 0.246±0.09. This means that ~25% of the risk of developing DSLD is genetic, with the remaining 75% of risk arising from environmental factors, such as training and shoeing, for example.

        Our research has shown that the genetic risk of DSLD in the Peruvian Horse is made up of many genetic variants across the entire genome. Each individual variant in an animal’s genome generally has small to moderate effects on disease risk that act additively. If an individual horse is born with many risk variants acting together, then genetic risk of developing DSLD will be high.

Genetic testing for risk of degenerative suspensory ligament desmitis in the Peruvian Horse

        We are now able to undertake genetic testing for DSLD in Peruvian Horses, which is complex diseases with moderate heritability. as we have a sufficiently large reference population made up of more than 200 Peruvian Horses mentioned above. To undertake testing, we will collect a DNA sample, obtained from a blood sample or a hair bulb sample from hairs pulled from the mane or tail. SNP marker array genotyping is then performed using the Thermofisher Axiom Equine array. The SNP marker data from the reference population is then used to predict whether a Peruvian Horse will develop DSLD. Using our reference population, our predictive testing has an accuracy of ~90% for predicting Peruvian Horses as a DSLD case or control. We expect this accuracy to improve over time as our reference population gets larger. Because this type of genotyping is run using plates of 96 samples, there may be some delay before the test result is available. In this regard, the more samples we test each week the quicker will be the turnaround time for the results.

        Because the genetic screening test only uses SNP markers and sex of the horse, testing can be performed on horses of any age including young foals. In this scenario, the young horse will not yet have developed the disease. Predictive testing as a DSLD case means that the individual horse has high genetic risk for the disease. In such horses, health management should focus on addressing environmental risk to minimize the likelihood that DSLD will develop later in life.

        With regards to breeding, consistent breeding of Peruvian Horses with low genetic risk of DSLD will lead to reduced disease prevalence in the population over time. Because DSLD is a complex disease, affected horses may still have a sire and a dam that never develop the condition. However, breeding horses with high genetic risk means that it is more likely that their foals will also have high genetic risk and develop DSLD during their lifetime.

Genetic testing for risk of degenerative suspensory ligament desmitis in other high-risk horse breeds

        Currently, we can only offer genetic testing for DSLD in the Peruvian Horse. Our current research is focused on work that will allow us to extend this testing to other high-risk breeds, such as the Akhal-Teke, Paso Fino, and the Warmblood as funding becomes available. This is a challenging research problem, but we are optimistic that we can develop predictive testing without having to spend many years build a large reference population for each breed of interest. We are currently working on developing across-breed predictive testing for the Paso Fino and Akhal-Teke breeds.

Implementation of genetic testing for degenerative suspensory ligament desmitis in the Peruvian Horse

        We are now setting up this genetic testing service at the School of Veterinary Medicine, University of Wisconsin-Madison. We welcome expressions of interest or questions about this important development in the Comparative Genetics and Orthopaedic Research Laboratory at the University of Wisconsin-Madison.

Questions or interest in genetic testing for degenerative suspensory ligament desmitis in Peruvian Horses

Please contact SVM Genetics –