When it comes to breeding horses, genetic diversity is the name of the game. Inbreeding reduces genetic diversity, which raises the risk of inherited disorders, limits adaptation to environmental changes, and can decrease health, performance, and survival rates. In the past, breeders would look at a horse's pedigree to estimate how much inbreeding had occurred using a fixed formula. The problem with that is neither we nor our horses inherit our genes in such a straightforward way, which means the results of this formula are often not nearly as accurate as they could be. With the advanced genetic testing used in the Etalon Equine Genetics' Ancestry Package, breeders and owners have a better tool to measure and understand their horse’s unique level of inbreeding: the Genomic Inbreeding Value.

What Is the Genomic Inbreeding Value?

Think of the genomic inbreeding value as a measure of how much of a horse’s DNA is identical because it comes from the same relatives. Traditional methods use the horse's family tree to guess this using a formula, often called the coefficient of inbreeding (COI), but Etalon's genomic approach looks directly at the horse’s unique DNA. This gives a more accurate picture of how closely related a horse is to its ancestors.

Why Should We Care About Inbreeding?

Inbreeding is a double-edged sword. On one hand, it can help future foals inherit specific desirable traits, but on the other, it can lead to serious health problems caused by harmful recessive genes and decrease the horse’s overall performance. For example, a study on Thoroughbred horses found that a 10% increase in inbreeding reduced the chance of the horse ever racing by 7%. Put simply, this means that as the amount of inbreeding goes up, performance goes down.¹

With genomic inbreeding data, breeders can make smarter decisions. According to their family tree, two full siblings might have the same amount of inbreeding, but their genomic inbreeding value might differ. This happens because they don’t inherit exactly the same DNA from their parents.

How Does Genetic Ancestry Testing Help?

The Ancestry Package from Etalon Equine Genetics gives breeders a genomic inbreeding value that comes from analyzing the horse's actual DNA. This is much more reliable than just looking at the horse's pedigree and using a fixed formula because that’s not how we inherit genes from our parents - it is much more random! The Ancestry Package checks the horse’s genetic material that is inherited from both parents to see which parts are identical because they come from the same ancestors.

This helps breeders:

• Understand Inbreeding Better: Instead of just guessing based on the pedigree and the traditional inbreeding coefficient formula, breeders can see the true genetic relationship between their horses.
• Make Better Breeding Choices: By knowing the genomic inbreeding value of their horses and potential mates, breeders can predict the inbreeding value of future foals and make choices that keep the gene pool diverse, creating more resilient horse populations.
• Improve Health and Performance: Relying less on inbreeding reduces the risk of genetic issues and can increase the chance that a horse will perform well due to a greater amount of genetic diversity.

It’s also important to note that pairing two horses with low genetic inbreeding values doesn't guarantee that their foal will also have a low value if the sire and dam are closely related. This is because the genetic inbreeding value only measures the overall likelihood of inheriting identical genes due to shared ancestry. Even if both parents appear genetically diverse, their foal could inherit identical gene copies if they share close relatives in their pedigrees, increasing its inbreeding value.

So while a horse’s genetic inbreeding value is important, comparing its pedigree to their potential mate’s is crucial when making breeding decisions. Reviewing both genetic data and family lineage can provide a clearer picture of potential inbreeding risks and help anyone hoping to breed their horse make more informed choices to maintain genetic diversity and health in future generations.

Practical Example

Picture two foals, both sired by the same stallion but from different dams. Traditional methods might predict similar inbreeding levels based on the shared sire, but genomic testing could reveal significant differences. This could be due to the specific genetic content each foal inherits from their dam and sire. Even full siblings can show varied genomic inbreeding values due to the random nature of genetic inheritance.

We have also seen plenty of examples where a horse’s calculated inbreeding value based on pedigree analysis and the mathematical equation is significantly different from their actual genetic inbreeding value as determined by their DNA. In either case, using a horse’s genetic material to determine their inbreeding value is the clear winner in terms of accuracy compared to using a fixed formula.

The Takeaway

The genomic inbreeding value from Etalon’s Ancestry Package is a game-changer for breeders. It gives a precise measure of inbreeding based on a horse’s actual DNA, not just its pedigree. This information helps breeders make better choices to keep their horses healthy and genetically diverse, leading to stronger and better-performing horses in the future.

Whether you’re looking to breed better horses or better understand your equine partner down to their DNA, understanding your horse’s genomic inbreeding value is key to making sure they have the best chance to be healthy and successful.

Ready to learn more about what our Ancestry testing can offer you beyond their genetic inbreeding value? Check out some of our other blogs and podcast episodes to take a deep dive into all things ancestry!

How To Read Your Horse's Test Results: Ancestry, Composition, and More

How to Read Your Horse's Test Results: Breed Composition

Rescue Horse Mystery: A Story of Love, Family, and Equine DNA

Map-My-Mustang: Elisa Wallace

References ¹ Hill, E. W., Stoffel, M. A., McGivney, B. A., MacHugh, D. E., & Pemberton, J. M. (2022). Inbreeding depression and the probability of racing in the Thoroughbred horse. Proceedings of the Royal Society B: Biological Sciences, 289(1977). https://doi.org/10.1098/rspb.2022.0487.