Q: I am thinking of breeding from my Labrador and want to have all the necessary health tests carried out first. I have had her hips and elbows X-rayed and her eyes tested but I am confused over the various DNA tests. Do I need to have her tested for all these diseases and if any prove positive, does that mean I cannot breed from her?
A: The advantage of DNA testing is that not only does it indicate if a dog is affected by an inherited disease but it also determines the likelihood of the dog passing on the disease to its offspring. Consequently it enables owners to make informed choices of suitable dogs to use to avoid breeding clinically affected puppies.
For most genetic diseases, both parents need to be affected for the puppy to show signs of the disease. If only one parent is affected the puppy will be a “carrier” of that disease. Usually carriers are clinically normal though they can still pass the disease on to their offspring. If both parents are “clear” then all puppies of that mating will be unaffected by the disease.
If your bitch comes from a “clear” line (in other words, there is suitable evidence that her immediate ancestors were clear), there is little point in testing for that particular disease since she will also be clear. As long as you mate her to a clear stud dog, there is no chance of passing the disease on to your puppies. If a DNA test indicates that your bitch is either affected or a carrier, ideally you need good reason to breed from her. Most people would avoid breeding from an affected dog, particularly in a numerically large breed like the Labrador.
If there is good reason to breed from a carrier, it should only be bred with a suitably tested stud dog shown to be clear of the disease. The accompanying table (below) shows the genetic status of puppies born of these various options and how, using DNA tests, it is possible to avoid breeding affected puppies. TB