HOW TO BREED SENSIBLY WITH DNA TESTS
French Bulldog Clubs should look at any DNA test that is specific to the French Bulldog with regard to the numbers affected, the severity of the disease concerned, the impact on the animals health and well being and decide whether any animals need to be removed from the gene pool. Many breeders erroneously consider that affected dogs cannot be used. But the beauty of having a DNA test is that, in the main, no animal needs to be lost to the gene pool.
Club members need to understand a) how these diseases are inherited; b) how to sensibly use this information; and c) not lose any valuable breeding stock unnecessarily.
The vast majority of DNA tests currently available (>90%) deal with simple recessive diseases.
Simple recessive DNA diseases - possible matings
Normal/clear dogs are shown as ‘AA’
Carriers (heterozygous) are shown as ‘Aa’
Affected dogs are shown as ‘aa’
Where ‘A’ = normal dominant allele and ‘a’ = affected recessive allele. One allele comes from each parent.
As ‘A’ in this case is a dominant normal gene, all un-highlighted matings are acceptable.
Matings highlighted in red are not advised and should not occur.
Matings highlighted in pink are high risk but may be required from time to time. If done, all progeny should be DNA tested prior to sale.
There are 2 reasonably significant DNA disease tests available to the French Bulldog at this time, which are largely being underutilised. There are also tests for colour dilution, mainly for blue, but as this is not considered a major issue by many, it is less frequently tested (or used as a selection criteria for breeding). More tests are constantly being developed. Some of these may cover obscure diseases, while others may cover significant diseases within the breed.
HC (hereditary cataract) HSF4 gene—this is an early onset cataract disease, usually affecting both eyes which is seen within the first 2-3 years of life and is progressive (ie. they go blind). These cataracts can be removed surgically, which is expensive, but the dog should have reasonable vision afterwards. This condition can be tested and the affect, carrier and normal dogs readily sorted out.
Cataracts occur in many breeds, some are early onset, some are late. The incidence in the French Bulldog does not appear to be high in Australia. However the consequences of a young dog going blind where this can be avoided, should have breeders test for this condition when doing genetic profiles.
DM (degenerative myelopathy)is a disease that occurs at the other end of French Bulldog life. This is a devastating condition that gradually whittles away the mobility and effectiveness of the entire hindquarter. Unfortunately it occurs well after the age of breeding, usually 8-9 years and older. The disease affects the myelin sheaths of the spinal cord, affecting from mid thoracic area back, with the messages getting slower and slower to the hindquarters. The only good part of this disease is that it is not painful to the dog. The disease course runs some 12-18 months with affected dogs usually being euthanised due to inability to stand etc.
This disease has been found in many breeds, over 135 breeds at last count (and in mixed breeds). The DNA test has been available only over the last 4-6 years. This disease is inherited as a simple recessive condition but it is complicated by a late onset which can vary from as early as 8 years to very late, to the point the dog may die from other conditions, without exhibiting any obvious signs. It appears that there may be additional triggering factors that then cause the disease to manifest as the dog ages. There is considerable research ongoing in this area that may hopefully clarify the situation.
As a result, DNA affected dogs with DM are being called “at risk” rather than affected, as only 1 in 2-3 will physically become affected prior to their death.
The number of physically affected older dogs that are seen would be in the order of around 1-2% of older French Bulldogs. Many of these may be misdiagnosed as having disc or other spinal issues which are not uncommon in the Frenchie. Some dogs may be unlucky enough to be affected with several of these conditions concurrently.
The current carrier rate is estimated around the 8-10% level.
Breeding Advice and DM
There is a certain recent degree of concern in regards to this condition. This is totally unnecessary. The aim of any DNA test is to clearly sort out the various categories of normal, carrier and in this case “at risk” animals.
The whole point of having a test is that we can avoid breeding any more “at risk” dogs very easily. At risk and carrier dogs and bitches should ideally only go to normal partners, the absolute worst that can be produced is a carrier. Gradually over time the incidence of the gene can be lowered in the population. Our aim is to reduce the incidence of severe disease in our breed, NOT to reduce the genetic variability (and viability) of our population.
The more diseases we try to control, the slower our overall progress, we need to move carefully as any sudden contraction in the gene pool often results in other conditions coming out of the “woodwork” as a result of the reduced viability of the remaining population.
Whilst I do not believe that we need to do extensive testing of breeding stock at this stage, it would be worth testing heavily used stud dogs, or bitches which kennels are based on in order to give breeders more information when making breeding decisions. Where major animals within the kennel have subsequently developed DM in their old age, ideally test retained progeny and take care with selecting clear breeding partners.
The number of cases of DM and HC are under reported. Use of the Health Report can assist us in ensuring we are improving the overall health of the breed as well as giving us more accurate statistics.
SNIP tests—when DNA testing SNIP tests are now available that will test all known (and recognised) diseases in any breed. These will also test for parentage (where generational data exists). It is now cheaper to test this way than for individual disease testing. Current costing is around $60-65 for 1 disease and around $135 for 3-4 diseases plus parentage.
Dr Karen Hedberg BVSc