What are estimated breeding values (EBVs)?
Estimated breeding values (EBVs) predict whether a dog is more or less likely to have, and pass on, genes related to a particular health problem. EBVs link information about dog's family with data on whether they, or their relatives, have this health issue and to what degree. EBVs can then be used to tell us how an individual dog compares to the rest of the breed.
In dogs, EBVs are often used for health conditions that are inherited in a complicated way. For these health issues, a dog’s genes increase or decrease the chances of them being affected, but this is also influenced by their lifestyle, diet, amount exercise etc.
More on complex inherited disorders
The risk of a dog developing a complex inherited disorder, such as hip or elbow dysplasia, is influenced by both environmental factors (e.g. diet, exercise or factors when in the womb before birth etc.) and genetic factors (the genes a dog has).
Each dog will have a mix of both “good” and “bad” versions of genes that individually increase, or decrease the risk of becoming affected by the condition. The impact one version of a gene has might only be slight, but lots of genes having a small influence, both positive and negative, will have a complicated combined effect, making it very difficult to predict whether, or to what degree, a dog will be affected. Only a dog’s genes can be passed on to its offspring.
Our EBVs for hip and elbow dysplasia
The impact that a lifetime of environmental factors (i.e. diet and exercise) has on a dog’s joints tends to be more noticeable as they get older. To make sure that our EBVs are a good reflection of a dogs genes, rather than their environment, we use hip and elbow data collected when the dogs are between one and four years old.
Why use EBVs?
EBVs are a more effective way of reducing the risk of producing puppies with hip and elbow dysplasia than by only using the sire and dam's individual scores.
These conditions are partly influenced by environmental factors and by better understanding a dog's risk it can lead to faster progress in reducing the prevalence of disease in the breed.
Find a dog's EBV score
Our Health Test Results Finder can help you find a dog's EBV score, as well as any DNA tests and health screening schemes that we record. This tool can help you make informed decisions, whether you're a breeder trying to find a suitable healthy mate for your dog, or a puppy buyer wanting to know more about the health of a puppy's parents.
Understanding your dog's EBV score
- Your dog's EBV score will always be calculated in relation to the breed average (which is always set at zero)
- Dogs with a higher than average risk of passing on genes for hip/elbow dysplasia will have an EBV higher than zero (i.e. a positive number, e.g 10). The higher the number the greater the risk
- Dogs with a lower than average genetic risk of hip/elbow dysplasia will have an EBV lower than zero (i.e. a negative number, e.g. -10). The lower the number, the less the risk
- A dog's EBV can change during its lifetime, either upward or downward, as more information becomes available, either about the dog itself or its relatives
- At birth a puppy’s EBV will be the average of its parents’ EBVs, e.g. a sire with and EBV of -5 and a dam with an EBV of +5 will produce a litter or puppies with an EBV of 0
Understanding your dog's confidence score
- The confidence indicates how much scoring information has been used to calculate the EBV
- The more scoring information available, from the dog itself and/or its relatives, the more confident we are that the EBV is close to the actual genetic risk
- The confidence of the EBV can increase if more relatives are, or the dog itself is scored
Putting your confidence score into perspective
- A dog with just its own hip score, and no relatives scored. will have a confidence of about 60%
- A dog without its own hip score, but with the score of both parents, will have a confidence of around 40%
- A dog without its own hip score, but with only one parent scored, will have a confidence of around 30%
General breeding advice
Ideally breeders should use dogs that that have an EBV which is lower than average (i.e. a minus number) and preferably with a confidence rating of at least 60%. Dogs with an EBV with a confidence less than 60% can still be used, but the higher the confidence, the more accurate the EBV will be.
Lower doesn't have to be lowest
The lower the EBV, the better, but breeders do not need to search out the dogs with the lowest-risk EBV. Selecting animals with a lower-risk EBV than average will still lower the risk of elbow dysplasia in the breed as a whole.
EBVs help you make balanced breeding decisions
It is recommended that breeders make well balanced breeding decisions. At birth, each puppy will have an EBV that is the average of its parents. Therefore, dogs with an EBV which is higher than average can still be bred from, providing that it is mated to a dog with an EBV which is well below average (assuming that the confidence for both dogs is high).
EBVs help maintain genetic diversity
Previously, the best advice was to ideally use dogs with an elbow score of zero, which meant that many dogs could have been excluded from a breeding plan if their scores were a significant consideration. Excluding dogs from a breeding plan can have an impact on genetic diversity.
By using EBVs, it is reasonable to use a dog with less than ideal individual BVA/KC scores, as long as the EBV indicates low genetic risk with good confidence. In such cases the elbow condition of the offspring should be carefully monitored and preferably they should be elbow scored themselves.
Making balanced breeding decisions
As well as considering the implications of a dog’s EBV or hip score, there are other equally important factors to consider when deciding whether two dogs should be mated together, such as temperament, genetic diversity, conformation, other available health test results, the general health of the dogs etc. Your breeding decisions should always be well balanced, and take into consideration the qualities and compatibility of both the sire and dam that you are considering.
Questions and answers
Can the results of the scoring scheme or EBVs be used to precisely predict if future puppies will be affected?
Hip and elbow dysplasia are conditions which are inherited in a complicated way which is not yet fully understood by scientists. Due to the complex nature of inheritance of these conditions, it is still possible that affected offspring may arise from parents which have good EBVs. It is hoped that breeding appropriately from screened dogs will reduce the risk of producing affected offspring and using EBVs reduces this risk even further, but it must be stressed that this is not a guarantee.
How to make the most of EBVs
EBVs link all available pedigree information with data collected through the BVA/KC health schemes. The more breeders that make use of this scheme, the more confident the estimation of the risk of passing on the genes for either condition. By continuing to hip and elbow score, breeders are securing the future for countless other dogs by providing the information needed to continue estimated breeding values.
EBVs rely on good quality data - the best way to ensure effective EBVs is to get your dogs scored, and use EBVs to indicate genetic risk in your breeding decisions. Although EBVs are a more effective way of using the hip/elbow score information, they are not a replacement. Their calculation relies on a large quantity of good quality score data. EBVs are regularly recalculated to make use of new score data and to provide them for newly registered dogs, so it is essential that scoring continues.
Scoring individual dogs has tremendous value in indicating the actual degree of dysplasia present (or not) in an individual dog. The EBV estimates genetic risk - which is helpful for breeding - but does not take account of non-genetic factors which influence the severity of dysplasia. Hip/elbow scores remain the best diagnostic measure of hip and elbow dysplasia, and will allow/help owners to adjust known non-genetic influences (such as exercise intensity or duration) to minimise the effects of these diseases where they occur.
Why do only some breeds have EBVs?
The Kennel Club’s ability to provide EBVs is based on complex calculations, but is dependent on:
- the proportion of dogs scored in a breed
- the spread of those scored dogs across each pedigree
As more breeders continue to hip score their dogs using the BVA/KC schemes, more breeds will be added in the near future. In addition, EBVs can, in principle, be developed for a variety of complex diseases, so as more schemes are developed more conditions and associated breeds may achieve EBVs.
Updates may change a dog’s EBV
Although a dog’s genes do not change during its lifetime, the EBV is an estimate of genetic risk, and will change as more information becomes available. For example, at birth, a puppy's EBV is based on the hip scores of its parents and other relatives. As the puppy grows it may be hip scored itself, as may some of its siblings. This extra information will be used in the regular calculation of EBVs. Eventually that dog may be used for breeding, and some of its progeny may be hip scored too. This information will also be used. All this extra information will increase the confidence of the estimate and may result in changes in EBV.
EBVs will also change in another way too. The breed average is always set to zero. Therefore if the breed average changes and hip/elbow scores improve or worsen, then an individual dog’s score may become closer to, or further away from, the breed average. For example, a dog, whose hip score, and the hip score for all its family, is 10, will have a low EBV if the rest of the breed has a hip score of 20. If the breed improves and all dogs in the breed have a hip score of 5, then the dog with the score of 10 will have a high EBV.
Does this mean an end to hip scoring our dogs?
No. EBVs are simply a more effective way of using the information we already have. It is important to remember that the estimates are only as good as the data used in their calculation. No more hip scores would mean no more EBVs. Thus, the availability of EBVs does not mean an end to participating in hip scoring schemes, but does mean that greater progress can be made in genetic selection for low hip scores through the more effective use of score information.
Furthermore, stopping scoring is not a way to improve a dog's EBV; the confidence will decrease. The best way to ensure reliable EBVs is to continue to score and use EBVs as the indicator of genetic risk in your breeding decisions.
Finally, but importantly, a dog's individual hip score still has tremendous value in indicating the degree of dysplasia in that particular dog. The EBVs estimate genetic risk, which is more useful in breeding strategy, but to determine the management of non-genetic factors known to influence the severity of dysplasia the hip score remains the best diagnostic measure.
Estimated breeding values were created as a collaboration between The Kennel Club and The Kennel Club Genetics Centre at the Animal Health Trust. The Kennel Club gratefully acknowledges the technical input and advice of Professor John Woolliams (The Roslin Institute, University of Edinburgh) in the development of the models for calculation and presentation of EBVs. The Kennel Club gratefully acknowledges Professor Brian Kinghorn (The University of New England, Armidale, Australia) for advice on the visual presentation of EBVs.