Short-faced dogs such as pugs, bulldogs (known as English bulldogs in the US) and French bulldogs are among the cutest pets out there – looking very different to the wolves they descended from. Over the last few years these breeds have become increasingly common, partly thanks to advertising and their popularity among celebrities. In fact all three breeds are now in Britain’s top ten favourite dogs.
But these dogs are the result of an amazing transformation in appearance and temperament caused by selective breeding, which has come at quite a cost to the dogs' health. Around half of them have breathing problems that sometimes lead to overheating, exercise intolerance and sleep apnoea. Their large heads and narrow pelvises also cause problems in giving birth (forcing Caesarean sections for many if not most) and their skin folds can become infected. Their exposed eyes are also vulnerable to damage, with about 15% suffering prolapsed third eyelids and many having other types of eye damage. Quite a number of dogs in several of the breeds also succumb to back or hip problems.
So research geneticists have started to look at ways to reduce the intrinsic health problems of these breeds. A recent investigation of genetic variation in bulldogs showed that all the individuals examined had little genetic diversity in either paternal or maternal lines. The same was true for the diversity of some types of immune system genes, so that the ability of these bulldogs to respond to pathogens may be reduced, which may potentially also be connected to common allergies. The authors argued that the breed’s health could only be restored by breeding dogs with other breeds, rather than preserving the breed in its current closed state.
With colleagues including Jane Ladlow, Lajos Kalmar and Nai-chieh Liu, I have been doing both genetic and clinical analyses of bulldogs and other short-faced breeds. Working with breeders of bulldogs, we investigated the respiratory distress that many of these dogs suffer from. We started by developing a computer algorithm to interpret breathing traces taken from dogs at rest, allowing us to objectively identify the disease and quantify variation between individuals. This analysis, together with collection of DNA samples from the studied dogs, opened the way for accurate genetic analyses of the respiratory disease. On the way, we also gained information on the genetic health of the breeds we studied as a whole.