Gundog hereditary diseases are the product of decades of selective breeding for pure-bred, pedigree dogs. After generations of using closely related animals, it is hardly surprising that many of our favourite working dogs now suffer serious genetic disorders. David Tomlinson investigates the plight of the pedigrees.

For more on gundogs and breed purity, David Tomlinson considers outbreeding: essential for gundog survival?

GUNDOG HEREDITARY DISEASES

If you read Peter Moxon’s classic book Gundogs, Training and Field Trials (first published in 1952 and still in print) you will find that gundog hereditary diseases fail to get a mention. Moxon wrote about the diseases of the day – distemper, jaundice and hepatitis – but he didn’t have to concern himself with hereditary diseases because at that time they weren’t a worry. That’s not to say that there weren’t any, but any that had been recognised were hardly significant and not of serious concern to those who owned and worked gundogs.

How things have changed.

Six decades of selective breeding, often using closely related animals, has resulted in the genetic stock of many of our favourite working dogs being heavily flawed. Not surprisingly, our most popular gundog, the labrador, has the longest list of inherited diseases of which elbow, hip and retinal dysplasia are the most significant; these are very common and affect a considerable number of dogs but there are at least another 30 gundog hereditary disorders associated with the breed.

So long is the list that I’ve never heard of many of the gundog hereditary diseases on it. Take osteochondrodysplasia for example. The word describes a range of disorders characterised by abnormal growth of cartilage and bone. These disorders typically result in skeletal dwarfism, with the limbs of an animal being disproportionately short. I am unaware of ever having met a dog diagnosed with osteochondrodysplasia, but when I think of it, I have seen a number of abnormally short-legged labradors that were almost certainly suffering from this complaint. This condition is autosomal recessive, ie two copies of an abnormal gene must be present in order for the disease or trait to develop. Affected dogs – and their siblings – should not be bred from.

Though I may not have heard of osteochondrodysplasia, I’m all too familiar with many of the more common gundog hereditary diseases. Take PRA (progressive retinal atrophy) for example, a term that covers several types of inherited degeneration of the retina. It’s been a major concern in labradors for some years. There’s no treatment for PRA and infected dogs eventually go blind.

To understand the nature of these inherited diseases a basic knowledge of genetics is required. For example, a dog that carries PRA will have one copy of the normal gene and one copy of the abnormal gene, and it’s unlikely to go blind. If mated to a clear dog , 50% of the offspring will be carriers. Mate one carrier with another and the result will be 50% of the puppies affected, 25% clear and 25% carriers.

GUNDOG HEREDITARY DISEASES: LABRADORS

One of the most important labrador stud dogs of the last decade was a stylish and handsome yellow dog, FTCh Craighorn Bracken, winner of the 2001 retriever championship. Bracken was never tested for PRA and only later was he discovered to be a carrier for this gundog hereditary disease, by which time his semen had been exported around the world. The widespread use of popular but untested sires like Bracken explains why gundog hereditary diseases have become so widespread.

There’s no legal compulsion to test your dog or bitch for such diseases but most of the top breeders of working gundogs do take such matters seriously. There are DNA-based tests for many of the gundog hereditary diseases. The US-based company Optigen has pioneered health tests for PRA, and the procedure is quite straightforward. The animal is taken to its vet for a blood test and the sample sent by email to Optigen. The procedure costs about £150 but needs to be done only once in the dog’s lifetime.

Centronuclear myopathy (CNM), another hereditary disease in labradors, is routinely tested for by responsible breeders. Dogs affected with CNM have muscles that fail to function properly. There’s no cure. The mutation responsible was originally identified by a research group at the Ecole nationale vétérinaire d’Alfort in France. Using information from this research, the Animal Health Trust at Newmarket developed its own DNA test for the disease.

A disease that refuses to go away is hip dysplasia. There’s no DNA test for this condition; it has a complicated pattern of inheritance determined by an interaction of genetic and environmental factors. In humans, hip dysplasia is approximately 12 times more likely when there is a family history; the same is largely true of dogs. Dogs with hip scores above the breed’s average should not be bred from. If I were buying a labrador puppy I would only buy one whose parents and grandparents had low scores.

Conducting health tests on a dog is expensive and this is reflected in stud fees or puppy cost. However, it’s a price worth paying. Frustratingly, it does seem that as soon as we identify and come to terms with one disease another one comes along, but this seems to be inevitable if we insist on demanding pure-bred, pedigree gundogs.