HIPS SCORES FOR BREEDING DOGS
HIP IN THE UK – ROOM FOR IMPROVEMENT?
Breeders of many dog breeds choose to use the Kennel Club/ British Veterinary Association Hip and Elbow schemes to try and select the parents least likely to produce puppies with hip or elbow dysplasia. But is the scheme working? Some think not.
SLOW PROGRESS IN HIP SCORES
Research shows that years of hip scoring has increased the percentage of dogs with the lowest scores, but it hasn’t made much impact on the numbers with mild hip dysplasia or worse. So is there any point? The problem with these studies is that they are based on the results from images submitted to the scheme and these are not representative of the state of any breed as a whole. Firstly only a small percentage of dogs are selected as potential breeding dogs, in some breeds not all potential breeding dogs are tested, only sound dogs over a year are usually tested, and (despite the scheme rules) some vets don’t send in images of hips they think will get a poor score. The published results only reflect the better end of the spectrum and give very little data on the worst hips, or dogs which are diagnosed before 12months of age. As a GP vet I believe I see far fewer dogs that are lame with hip dysplasia at 6-12months, and less dogs needing treatment for hip arthritis before they reach 8-10 years old than I did as a young vet so I think hip scoring is doing a lot of good… but you can’t publish a paper without data.
THE BABY AND THE BATHWATER?
Researchers only consider hips with a total score under 5 as ‘normal’. Most dogs with scores of 6-10 will have no changes in their hips over time, and even dogs scoring up to 20 will probably suffer only manageable arthritic pain in old age. Whilst it may be the Holy Grail to produce only puppies with normal hips, it must always be remebered that a dog is more than their health tests. If we select too strongly for excellent hip scores we might lose temperament, type, working ability, and we will definitley shrink the gene pool which can lead to other genetic probems cropping up.
IMPROVING HIP SCORES IN THE UK
Hip scores could be reduced in UK dogs by adopting one or more of the following methods;
Score later
Taking images for hip scoring at 12months, as we do in the UK, could miss up to 30% of dogs which will go on to develop hip dysplasia in later life. Waiting until dogs are over 2 years old (as for the American OFFA scheme) reduces this to under 10%.
Score differently
The standard ventro-dorsal extended leg view used by most hip schemes makes the joint look tighter than it is in the standing dog. As joint laxity is the most heritable and most significant driver of hip dysplasia using a test that measure joint laxity allows us to predict whether a dog will get hip dysplasia more accurately. The PennHIP test can be done in young dogs (from 16 weeks) so is a useful screening test for breeders choosing which dogs to keep. It is less used than the BVA scheme as vets need extra training and certification, and positioning for the 3 images is more complicated and time consuming (in the USA dogs are often held for the films, in the UK holding dogs for non-emergency x-rays is forbidden).
Use genetic tests
So far we only have one genetic test for hip dysplasia. The Dysgen test looks at several markers which may reflect a higher predisposition to hip dysplasia. As yet the test is only validated for Labrador Retrievers, and there is little guidance on how it can be used to make breeding decisions.
Use estimate breeding values and vertical pedigrees
By looking at the scores of a dog’s relatives and offspring it is possible to get an indea whether they will produce puppies with scores similar to, better, or worse than their own. The Kennel Club publishes EBVs for dogs in some of the more common breeds but where a dog has few tested relatives the accuracy reduces.
Move the goalposts
At the moment the recommendation is to breed from dogs with a score equal to or less than the 5 year median (middle score) for the breed. Though logical to breed from average or better than average dogs, this does have challenges and limitations. As previously mentioned, the median score is calculated only from submitted images, so if there are lots of young lame dogs that aren’t scored the median could be artificially low. Alternatively, if a breed generally has poor hips the average may still be unacceptably high.
Research suggests that if we chose only to breed from the lowest 25 or 30% of dogs hip scores would come down more quickly. However, this could lead to a reduction in overall genetic diversity and selection for other issues. Alternatively we could look at the scores regardless of breed and suggest only breeding from ‘excellent’, ‘good’, and maybe ‘fair’ scores, putting ‘fair’ to ‘excellent’ (this grading is more similar to that used in Europe and America than our numbers based system). But again, if we focus in too much on hips, we risk creating new problems. And in some breeds there would be almost no dogs left to breed!
HOW TO USE HIP SCORES IN BREEDING PROGRAMMES
The aim of a breeding programme won’t be the same for every breeder. For working animals, such as Guide Dogs or Police Dogs, it may be important to produce as many dogs as possible with ‘normal’ hips to ensure a long working life. Here it may make sense to use PennHIP to screen potential breeding dogs at an early stage, and if using the BVA scheme to choose animals with a score of 10 or less. If a dog has other good characteristics but a slighty higher score (up to 14) they could be paired with a lower scoring mate, especially if they have a good EBV.
For pet dogs a good temperament is the most important thing, and buyers may be more accepting of a dog needing medical support for arthritis as they hit double figures. Using breeding dogs with scores under 15 and excellent temperaments is probably sufficient, and there shouldn’t be a temptation to use a very low scoring dog if they aren’t of sound temperament!
In a breed with a high average hip score or low numbers the aim might be to reduce the score of puppies more gradually. This may mean pairing above average scores with below average scores.
Some vets take a huge interest in breeding better dogs and are happy to discuss the results of your dog’s tests, or the result of teh parents of a puppy you are considering. Four Seasons Holistic Veterinary Care can’t take radiographs for the BVA scheme, though our vet also works at Companion Care Vets in Eastbourne (01323 649325) who can. We can offer telephone consultations to discuss results.