Screening that requires a specialist
A large number of breeds are predisposed to specific inherited eye conditions, many of which can be definitively diagnosed via DNA test. That said, it is important to conduct routine clinical eye examinations throughout the life of your dog in the same way that we get our eyes tested. As humans, we don’t necessarily go to an optician on a regular basis unless we have an ongoing issue or require corrective lenses, but we are able to recognise when we are experiencing something abnormal and can seek advice at that point. Dogs are not able to let us know when there is an issue, and without routine checkups, abnormalities may go unidentified and untreated.
It is recommended that dogs of all breeds undergo a clinical eye examination at least 3 times during their normal lifespan; the first around 1 year of age, and pre-breeding. The second at around 3-4 years of age and the last at around 7-8 years of age. Clinical eye examinations can give an early indication of a number of different health issues, not just eye-related, for example, raised blood pressure, anaemia, diabetes and lymphoma.
The Hereditary Eye Disease Scheme is run by the BVA in conjunction with the Kennel Club and the International Sheep Dog Society and is open to all breeds. You can book an appointment directly with a BVA appointed Ophthalmology Specialist near you.
As of April 2022, a routine eye examination for one dog starts at £60. The BVA offer discounts for additional dogs and group bookings and dogs over 8 years cost just £32. Litter Screening is also available for breeds known to have congenital (present from birth) inherited eye conditions, such as Collie breeds. After the examination, the panellist will provide you with an eye certificate showing your dog’s result and if your dog is KC registered, the result will automatically be published on the KC website Health Test Results Finder.
Glaucoma is an inherited condition whereby reduced drainage of the fluid (aqueous humour) that is produced within the eye results in a buildup of intraocular pressure within the eye causing pain and even blindness. Glaucoma is divided into two types: Primary Open Angle Glaucoma (POAG) and Primary Angle Closure Glaucoma/Primary Closed Angle Glaucoma (PACG/PCAG).
Gonioscopy is the technique used to determine if a dog has, or is at risk of, PACG/PCAG, by assessing the development of the drainage angle (the angle between the iris and the cornea). Defective development of the drainage angle is known as Pectinate Ligament Abnormality (PLA) or is sometimes referred to as goniodysgenesis (gonio = angle, dysgenesis = defective development).
Gonioscopy is carried out by specialist ophthalmologists (eye panellists) as part of the BVA/KC/ISDS Eye Scheme and you can book an appointment with them directly, but the technique requires specialised equipment, so make sure you specify that you want a Gonioscopy appointment to ensure your chosen panellist can perform this. The panellist will examine your dog, usually using local anaesthetic eye drops, and will then issue a certificate detailing your dog’s grade.
Dogs can undergo gonioscopy from 6 months of age, but their grade can change with age, so ideally gonioscopy should be performed at approximately 1 year of age, 3-4 years and then 7-8 years.
Grade classifications are:
- Grade 0 - unaffected, normal angle
- Grade 1 - mildly affected
- Grade 2 - moderately affected
- Grade 3 - severely affected
It is recommended that only dogs with a grade 0 or 1 are used for breeding. Breed-specific advice should be sought for dogs with grade 2 and those with grade 3 should not be used as part of any breeding programme.
As of April 2022, the cost for Gonioscopy is £60 per dog, or £54 if done in conjunction with a clinical Eye Examination (details above). On occasion, dogs require sedation to conduct the examination, which would be charged separately.
Please note that Gonioscopy cannot identify dogs with, or at risk of, POAG. A DNA test is available for this condition (see DNA tests for Autosomal-recessive conditions below).
Respiratory Grading Function Test
The Respiratory Grading Function Test is run by the Kennel Club in conjunction with the University of Cambridge and assesses the breathing ability of brachycephalic (flat-faced) breeds.
Brachycephalic Obstructive Airway Syndrome (BOAS) is a condition whereby excessive soft tissue in the nose and throat obstructs the airway making it difficult for affected dogs to breathe well or normally. It is a progressive disorder that can affect a dog’s ability not only to breathe normally but to eat, sleep and exercise.
Dogs can be assessed from 1 year of age and they should be reassessed every 2 years whilst being used for breeding.
Grade classifications are:
- Grade 0 - clinically unaffected, no respiratory signs of BOAS
- Grade 1 - clinically unaffected, mild respiratory signs of BOAS
- Grade 2 - clinically affected, moderate respiratory signs of BOAS (should be monitored)
- Grade 3 - clinically affected, severe respiratory signs of BOAS (requires treatment)
For breeds that can be affected by BOAS, you should only breed from dogs that have been assessed. Grades 0 and 1 can be used for breeding, as can a grade 2 as long as mated with a grade 0 or 1. Dogs of grade 3 should not be used for breeding.
You can book an appointment directly with a vet trained in BOAS assessment. Costs may vary depending upon the assessor, so make enquiries when booking.
Chiari Malformation/Syringomyelia (CM/SM)
Chiari-like malformation (CM) is a mismatch in brain size - that being too large - and skull size - that being too small - which can cause part of the brain to protrude from the back of the skull and can block the flow of cerebrospinal fluid around the spinal cord.
Syringomyelia (SM) is where this blockage causes fluid-filled pockets called syrinxes to develop within the spinal cord. Some dogs with mild CM/SM can appear normal and exhibit no obvious symptoms, but other dogs experience intense pain, increased sensitivity to touch, and may demonstrate an unwillingness to exercise, incoordination, ‘air-scratching’ and excessive paw licking.
This is another complex inherited disorder; the exact mode of inheritance is unclear, and genetic and environmental factors play a part, but it is shown to be inherited in the Cavalier King Charles Spaniel and the Griffon Bruxellois. It is suspected to be inherited within the King Charles Spaniel and has been reported in a small number of other breeds.
In order to screen your dog for this condition, you need a referral from your vet to either a veterinary centre with MRI scanning facilities or to a neurologist. The MRI image is then sent to the BVA where it is graded by a panel of neurologists and radiologists.
Both CM and SM are graded from 0-2. In the case of CM, 0 being no malformation and 2 being impacted or herniated and in the case of SM, 0 being no syrinxes and 2 being the presence of syrinxes.
Breeding advice is complex, but you should seek advice once your dogs’ grade is received. Dogs exhibiting clinical signs of CM/SM should not be bred from.
As of April 2022, the cost of grading is £100.
Brainstem Auditory Evoked Response (BAER) Testing
Some breeds are predisposed to congenital deafness. This is another complex condition and one that is thought to be controlled by many different genes, but there are some breed-specific characteristics that mean that puppies of certain breeds are more likely to be born deaf than others.
Those breeds that have a mostly white coat are considered more at risk, linking the condition to the ‘extreme piebald’ gene. There is also evidence that links the merle coat colour with congenital deafness.
Dogs of breeds that are considered at higher risk for deafness should be BAER tested before being bred from, although the ideal age to get this test carried out is between 5 ½ and 6 ½ weeks old, as puppies of this age will sleep following periods of activity, giving the specialist the perfect opportunity to conduct the test. This is also a good age as responsible breeders will want to have a litter tested before the puppies go to their new homes, as the training of deaf or partially deaf dogs can be difficult, especially if the owner is not aware that there is a hearing problem.
Some deaf dogs will exhibit unpredictable behaviour due to being startled by movement or sounds that a dog of normal hearing would be aware of. They are also more at risk to everyday dangers such as traffic.
The BAER test will determine if a dog is:
- bilaterally deaf - deaf in both ears,
- unilaterally deaf - deaf on just one side
- normal hearing.
Unfortunately, offering definitive breeding advice is not yet possible due to the varying factors involved in inheritance, but scientists would suggest that only bilaterally normal individuals should be bred from.
You can book an appointment for individual or litter screening directly with a registered Test Centre near you. You need to take a copy of the BAER Test Report Form with you.
As of April 2022, individual screening costs £116.14 plus the cost of a certificate should you want one. Litter screening costs £68.89 for the first puppy and then £31.92 for each additional puppy in the litter. Again, certificates are at an additional cost.
There are a huge number of DNA tests available which are an invaluable resource to not only better understand your dog’s genetic makeup, but to protect future generations of your chosen breed and to give peace of mind that the puppies you are producing are as healthy as they can be.
Fully understanding the health status of your breeding stock before planning your breeding programme is imperative and responsible breeders should be utilising all available tools to reduce the chances of passing on known inherited conditions and producing affected puppies.
DNA tests fall into the following 4 categories:
DNA tests for Autosomal-recessive conditions
With autosomal-recessive conditions, a dog must inherit two copies of an abnormal gene - one from its mother and one from its father - before it will be affected by that condition. The majority of available DNA tests are for autosomal-recessive conditions and, unlike the complex inherited conditions discussed above, interpretation of these results is straightforward and clear breeding guidance can be given.
A dog can be:
Clear - they have no copies of the abnormal gene, will never develop that condition and cannot pass the condition on to future generations. Clear dogs can be mated to any other without producing affected puppies, however, if bred with a carrier dog, they may produce carrier puppies and if bred with an affected dog, all puppies will be carriers.
Carrier - they carry one copy of the abnormal gene but will never develop the condition themselves. Carrier dogs should only be mated to clear dogs. Mating a carrier to a carrier runs a 25% chance of each puppy being affected. Mating a carrier to an affected dog runs a 50% chance of each puppy being affected, with the remainder being carriers. No puppies from a carrier to affected mating will be clear of the condition in question.
Affected - they carry two copies of the abnormal gene and will develop the condition in question. Affected dogs can only be mated to clear dogs to avoid producing affected puppies, however, all puppies will be carriers themselves so the use of affected dogs should be avoided unless under specific and well-considered circumstances.
DNA tests for Autosomal-dominant conditions
An autosomal-dominant condition means that a dog only needs to inherit one copy of an abnormal gene, from either its mother or its father, before its health is affected. As such, interpretation is a little more complicated, but breeding guidance can be given.
A dog can be:
Clear - they have no copies of the abnormal gene, they are highly unlikely to develop the condition and will pass on a normal copy of the gene to their puppies.
Heterozygous affected - they have one copy of the normal gene and one copy of the abnormal gene. They are likely to be affected by the condition and could pass on a copy of the abnormal gene to their puppies.
Homozygous affected - they have two copies of the abnormal gene, are likely to be affected by the condition and will pass on a copy of the abnormal gene to their puppies.
Only clear to clear matings will produce a litter of clear puppies.
Most DNA tests look for a particular gene that is known to cause a particular condition. Where the exact gene cannot be identified, sometimes it is possible to determine where it is located in the dog’s genome and scientists can then identify a section of DNA that the gene is linked to and that it will be inherited alongside. This is known as a linked genetic marker, and can predict with a high level of confidence, the genetic status of a dog in relation to the specific condition.
Laboratories often provide an estimate of how accurate their linkage test is. The interpretation of these results is the same as for Autosomal-recessive conditions.
Risk-based DNA tests
For some conditions, certain environmental factors, or other genetic influences can also contribute to whether a dog becomes affected. Having copies of the disease-causing genes will not necessarily be a guarantee that the condition will occur and an absence of these genes will not necessarily be a guarantee that the condition will not occur.
Risk-based tests can be less accurate than other DNA tests, but they are still sufficiently accurate to be worthwhile and, as with the linkage tests, laboratories will often provide an estimate on how accurate their test is.
A dog can be:
- Minimal risk (0) - they do not have any copies of the abnormal gene and are at significantly reduced risk of developing the condition.
- Minimal risk (1) - they have one copy of the normal gene and one copy of the abnormal gene. They are at reduced risk of developing the condition and could pass on either a copy of the normal gene or a copy of the abnormal gene to their puppies
- Increased risk (2) - they have two copies of the abnormal gene, have an increased risk of developing the condition and will pass on a copy of the abnormal gene to their puppies.
Only minimal risk (0) to minimal risk (0) matings offer the lowest chance of each puppy in the litter not developing the condition and these puppies will not be passed a copy of the abnormal gene variant.
Most DNA tests are easy to conduct, require you to take a simple swab from inside your dog's mouth - usually from their cheek - and then send the sample to your chosen laboratory for analysis. Only a small number of DNA tests require a qualified person to take a blood sample from your dog.
Costs vary from laboratory to laboratory and depending upon the test type and condition, but it is worth bearing in mind that there are a number of unregulated laboratories across Europe from which the validity of results is unproven. Make sure you check the credentials of your chosen laboratory or use one approved by the Kennel Club. The Kennel Club also offer some cost-effective breed-specific CombiBreed packages for breeds where multiple DNA tests are recommended.