The fight against blindness in Labradors

Did you know that there is a nasty disease that could cause our lovely Labradors to lose their sight?

Progressive blindness (PRA) has long been a problem disease in our breed, as it is in several other breeds of dog.

It is therefore important for Labrador owners, and especially prospective Labrador puppy owners, to be aware of what it is and what we can do about it.

What causes this blindness in dogs?

Progressive retinal atrophy or PRA is the breakdown or destruction of the retina.

The retina is a membrane that lines the back of the eye.

It is this damage to the retina that the vet is looking for when he examines the dog’s eye with his ophthalmoscope.

There are a group of diseases that cause PRA.

The type we see in Labradors is prcd or ‘progressive rod-cone degeneration’. Rods and cones are the light receptive cells that cover the surface of the retina.

Annual eye exam

We have had a diagnostic test of sorts available to us for over twenty years now, in the form of an annual eye examination for dogs.

This important test has helped to prevent the spread of this inherited diseases, but it isn’t perfect.

The problem with this standard eye exam is that it only gives us limited information.

The limitations of the physical examination

It tells us whether or not the dog has any symptoms of eye disease at the time of the examination.

It does not tell us whether he or she will be likely to develop the disease later in life.

This means that the standard eye exam must be carried out at regular intervals in order to ensure that the dog remains healthy.

And it doesn’t necessarily exclude dogs which are affected by this eye disease from the gene pool until after they have been bred from, as the disease does not always show itself until later in life.

Until recently this test was all we had to go on, when trying to breed dogs free from progressive blindness.

How is the disease inherited?

A gene has been identified, which when faulty has the potential to cause prcd-PRA in Labradors and other breeds of dog.

Every dog will inherit two copies of the gene, one from each parent.

And if both copies are healthy, the dog can never develop this form of blindness and cannot pass the disease on to its offspring.

If the dog is unfortunate enough to have two faulty copies of the faulty gene it will go blind at some point in its life, and will pass a copy of the gene on to each of its offspring.

If the dog has one faulty copy of the gene and one healthy one, it will be unaffected by the disease but will pass a copy of the faulty gene on to some of its offspring.

Making good breeding choices

If a dog develops the disease we know that he must have two faulty copies of the gene and that therefore both his parents have at least one copy each.

Our understanding of this mechanism of inheritance has helped us to establish that some dogs are carrying the faulty gene and to remove them from the gene pool.

Protecting the gene pool

Not all of these dogs which have passed down the gene will go on to develop the disease, many will simply be carriers.

But until the Optigen test came along we had no choice but to remove them from the gene pool completely.

This is a bad thing in any pedigree breed because the genes in our ‘pool’ are all we will ever have to work with, and we don’t want to lose any more of them than is absolutely necessary.

The optigen test has helped us make better breeding choices.

What is so great about the Optigen test?

From a DNA sample (cheek swab or blood), the Optigen test can specifically determines whether or not the dog being tested has two healthy copies of the gene, two faulty copies or one of each.

If he has two healthy copies he is designated as ‘clear’ of prcd-PRA. If he has two faulty copies he is designated ‘affected’ and if he has one copy of each he is designated a ‘carrier’.

The optigen test is giving us a lot more information than the old eye exam, specifically it enables us to tell carriers and affected dogs apart, long before the affected dog’s eyes begin to deteriorate.

Because it tells us about the genetic makeup (genotype) of the dog, it only has to be done once.

What is more, puppies from two ‘clear’ parents need never be tested, they cannot possibly inherit what neither of their parents possess and are therefore ‘clear’ by parentage.

Perhaps the best thing about Optigen is that it allows us to breed from carriers, an act that some people find hard to understand initially.

Why breed from carriers?

Having the ability to breed for dogs which carry the faulty prcd-PRA gene is highly beneficial to the breed, because it maximises the gene pool.

Within any breed of dogs that are contained within a closed gene pool there is an increasing risk over time of new diseases appearing, and this risk increases as the gene pool diminishes.

Each generation has its favourite stud dogs and these tend to be used extensively on female dogs all over the country. Restricting matings to those between dogs which are clear of prcd-PRA and an increasing range of other conditions for which tests are available, has the potential to reduce the gene pool even further.

Better breeding

The last thing we should be doing is limiting our choice of breeding stock even further

Enabling matings to take place between clear dogs and carriers, gives us a far greater choice of mates whilst ensuring that no puppies are born which will suffer from these diseases.

Maintaining genetic diversity is crucial if we are to maintain the health of our pedigree dogs, and the Optigen test is another weapon in our arsenal in the battle against disease.

Is it OK to buy a puppy if one parent is a carrier?

Provided that your puppy has one parent that is Optigen tested ‘clear’  then your puppy cannot ever develop this form of PRA, even if the other parent is a carrier.

It is therefore safe to purchase such a puppy, provided all other health checks are in place.

Never buy a puppy from a carrier if the other parent has not been tested, unless your puppy has itself been tested before purchase.

If you do not know that your puppy is ‘clear’  by parentage (ie both parents are ‘clear’), you should have your puppy tested should you ever wish to breed from her.

If she turns out to be a carrier herself, you will simply need to ensure that she is mated to a ‘clear’ dog in order to ensure her puppies are healthy.

A useful tool

The Optigen test is not a cure all,  and there are other causes of blindness in Labradors.  For this reason it is still a sensible precaution to buy puppies from breeders that also carry out the annual eye check.

However, this relatively recent addition to the battery of tests that many Labrador owners now embark on before breeding from their dogs,  offers long term benefits to the health of the breed by eliminating affected dogs from our breeding stock before they show symptoms and by enabling us to maximise genetic diversity through breeding from carriers where appropriate.

More information  can be found here

• Health Screening for Labradors
• Common myths about health testing
• BVA/KC Hereditary Eye Disease Screening
• Optigen

If you would like to share you own experiences of PRA blindness,  please feel free to leave your comments below.

More information on puppies

(paid link)For a complete guide to raising a healthy and happy puppy don’t miss The Happy Puppy Handbook.

The Happy Puppy Handbook covers every aspect of life with a small puppy.

The book will help you prepare your home for the new arrival, and get your puppy off to a great start with potty training, socialisation and early obedience.

The Happy Puppy Handbook is available(paid link) worldwide.

This article was first published on the 2nd of November 2011, and has been fully revised and updated for 2015.