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What are EBVs and how do they help?
What are EBVs?
Estimated Breeding values (EBVs) are a genetic selection tool we can use to figure out which breeding dog has better genetic merit for certain desirable traits, compared to other dogs of its breed. Instead of relying entirely on phenotype (observable traits) we can consider genotype (genetic traits), which give us more reliable results because they are not influenced by the environment.
The interesting thing about EBVs is that they incorporate data not just from the dog in question, but also its relatives and progeny. Over time, we gain a more accurate understanding of the real genetic merit of the dog and other dogs within its line. Eventually, this allows us to make better informed decisions about things that otherwise would have been based on observation and assumptions – some examples of which include:
- Which breeding dogs to pair: which breeding pair is most likely to produce puppies more ideal for your program (based on the traits you’re looking for – like improved hip health or certain temperamental traits)
- Selecting your next generation of breeding dogs: which progeny of a particular breeding dog are most likely to produce improvement in certain traits
- Genetic likelihood that a dog may develop a health or behavioral issue: Allowing us to implement preventative care and early screening procedures
- Comparison of genetic merit within your breed: Does this dog improve his breed? Is he a worthy breeding candidate?
Estimated Breeding Values have been used in cattle for some time and with great success, but the application of EBVs for working dogs is a comparatively new concept and one made available to working dog organizations thanks to the International Working Dog Registry. Because of this, dog-specific examples of what EBVs are and how they help are limited – although we provide many educational materials targeted specifically to dog breeders in the resources you’ll find on this website. In addition, however, we’ve found a few resources that can help explain some of these concepts as seen in human medicine. The terms used in the below video (“Polygenic Score”) are different, but the concept is exactly the same.
Video from the Broad Institute, available on Youtube: https://www.youtube.com/watch?v=HwEAjZWPw2k
An EBV is a number
Just like the “Polygenic score” in the video above, an EBV is a number. It is calculated from whatever health and behavior data is available about that dog, its relatives, and its breed. In the International Working Dog Registry, EBVs are most accurate for Labrador Retrievers, Golden Retrievers and German Shepherds as those are the breeds most commonly entered into the database and therefore have the most health and behavior data available for EBV calculations.
The actual EBV is a number from 1 to -1 as seen in the example below. However, to make EBVs more user-friendly, the IWDR provides a percentile ranking of the dog, based on its raw EBV data, so you know at a glance where that dog stands in comparison to your other candidates and the other dogs of its breed. Breeding managers most often use the percentile ranking (100% is the best you can get, so the higher your percentage, the better).
Below is an image showing some example EBV data. You can see corresponding percentage rankings for each EBV. For example, dog Curtis has a Noise EBV of 0.35 which translates to Curtis being in the 95th percentile (e.g. top 5%) of his breed for the “Noise” trait.
How EBVs help
As you can tell, there is a lot of science that goes on behind EBVs, but will they actually improve your breeding program that significantly? In order to answer that question, we need to consider the benefits and disadvantages of EBVs compared to other typical selection methods.
Phenotype Selection
The most common type of genetic selection is phenotype selection. This method involves studying phenotype data on the dogs under consideration, including the data you can gather on their relatives. Most of that data comes from:
- searching online registries for health clearances and performance titles
- speaking with other breeders/organizations
- and observing dogs performing in behavior tests, work, shows or competitions.
- You may also use tools to assess and preserve genetic diversity while practicing line-breeding to intensify desired phenotypes (for example, calculating inbreeding coefficients to maintain a level of genetic diversity during line-breeding).
Additionally, phenotype selection involves the use of expansive genotype tests available from commercial laboratories, which are required to reduce incidence of genetic diseases. Test results can be helpful, especially in choosing mates that will not produce affected progeny, however, many traits of concern for breeders are polygenic (influenced by two or more genes), and genetic tests for polygenic traits have not been developed or are unreliable. The downside of relying solely on genotype testing as a scientific assessment of genetic merit is the overwhelming challenge of trying to effectively use the data to systematically increase the frequency of desired genes (or traits).
There are some other risks when relying on phenotype selection: unfortunately, not all relatives are represented and often, registries only report information on unaffected (“Normal”) dogs. You may be forced to rely on second or third-hand subjective opinions on a dog’s performance or behavior. You may be subject to selection bias, where only some pieces of the whole story are made available for you.
The most frustrating aspect of phenotype selection is that despite all of the cost and effort invested, breeders are still at the mercy of chance to systematically improve their dogs’ health, behavior, working ability and conformation simultaneously while maintaining genetic diversity in the population. With the ever-increasing number of genotypes being reported and other tools now available, even the most adept breeder studying the data of dogs and their relatives cannot adequately estimate the relative genetic value of the underlying genes and how they will interact across loci in the next generation.
- Learn more on making breeding decisions without EBVs here, This presentation by Madeline Zimmermann is only available to IWDA members.
EBVs as a Selection Tool
It was in order to reduce this dependence on chance that EBVs were initially utilised in the service dog world, which had a demand not only for improving genetic and lifelong health but also to consistently breed more dogs with particular working temperaments. These statistical calculations, developed by quantitative geneticists, allow breeders to know which young dogs are statistically more likely to possess more of the desired genes, and they take into account all traits for which data is kept and EBVs are available.
As we mentioned earlier, current EBV data in the IWDR is most accurate for Labrador Retrievers, Golden Retrievers and German Shepherds. Over time, organizations have worked with the IWDR to define which traits they need to improve through genetic selection, and assessments have been made to confirm which traits are most heritable and therefore worth including in EBV calculations.
- Learn more about EBV accuracy here.
- Why are EBVs different for littermates? discusses heritability of some traits used in EBVs.
When used properly, EBVs have been proven to work – they have been shown to rapidly and reliably improve the traits selected for.
At the end of the day, EBVs are another tool to add to your toolkit. They do require a level of dedication to work effectively, which starts with consistent and accurate data collection from many dogs of a certain breed, including not just your dog but also their relatives. EBVs are not a tool to be taken lightly: breeders should not disregard dogs with lower scores or genetic diversity for the sake of breeding for a high EBV. There are also other influences that may impact your progress as you work towards your breeding goals.
You can find out more about Estimated Breeding Values at the following link, and navigate through more of our materials in the Additional Resources below.
Additional Resources
- How to use EBVs
- Does using Estimated Breeding Values cause the Inbreeding Coefficient to increase?
- What data should I collect?
- What is a selection index?
These resources are only available to IWDA members. Not a member? Become one today.
- How to use estimated breeding values successfully – presentation by Madeline Zimmermann
- Improving health using EBVs: Elbow, Skin and Mast cell tumours – presentation by Madeline Zimmermann
- Improving behavior with EBVs: Body sensitivity, Noise Fear, Inhibited by Stress, Activated by Stress, Excitable – presentation by Jane Russenberger