“A tough pill to swallow”
Finding the genetic cause of congenital oesophageal dysmotility in dogs
Some dogs are born with a hereditary condition that disrupts the movements (peristalsis) of the oesophagus. The defect is particularly common in certain breeds, such as the white Swiss shepherd dog, German shepherd, Weimaraner and Irish setter. Its severity can range from a mild disruption of peristalsis with virtually no discernible symptoms to full oesophageal paralysis (mega-oesophagus). The Academic Veterinary Hospital now offers screening programmes for breeding animals and puppies aimed at detecting the disorder.
The Expertise Centre Genetics of Companion Animals of the Veterinary Faculty studies the genetic causes of this disorder. “While congenital mega-oesophagus gives severe clinical symptoms, dogs with a less severe oesophageal dysmotility show no or mild symptoms, like excessive burping, refusing to eat dry food or stretching the neck while eating”, explains Hille Fieten, associate professor in clinical genetics and internal medicine specialist. “Owners may not recognise these symptoms and affected dogs may be used for breeding. In this way, the disease can spread through the population undetected. A barium contrast fluoroscopy of the oesophagus is now used at the Academic Veterinary Hospital to detect milder forms of oesophageal dysmotility. Together with the radiologists, we developed a scoring system to help classify the severity of the dysmotility. In addition, we collect DNA samples from the dogs to investigate the DNA mutations that cause this disorder. We aim to contribute to developing effective breeding strategies to decrease the frequency of the disorder in current dog populations.
The veterinarian takes a standardised history from the dog owner, asking about the type of food and any clinical symptoms the dog may have, and performs a physical examination. Researchers later compare the reported clinical signs with the severity score of oesophageal dysmotility to study whether there is an association.
First, a chest X-ray is taken to exclude congenital mega-oesophagus. If there are no indications for a megaoesophagus, a barium contrast fluoroscopy of the oesophagus is performed.
The radiologist evaluates the swallowing motion and movement of food from the mouth through the oesophagus to the stomach. The test is taken in the most natural position by placing the dog in a transparent cage and subsequently feeding it soft food and kibble mixed with barium contrast. As the dog eats, the X-ray technician traces the position of the food using a movable X-ray tube (grey cube with yellow sticker). The monitor reveals real-time images of the food travelling from the mouth to the stomach.
Friends of VetMed support the project ‘Healthy Breeding’, where scientific research is performed to develop innovations for sustainable breeding strategies of companion animals. Would you like to support this research? Please click here.
Screening for abnormalities helps to breed healthy dogs.
Breeder Mark Wisman has the puppies of his Swiss white shepherd screened for oesophageal paralysis
“As a breeder, you obviously want to breed healthy dogs”, breeder Mark Wisman explains. “It’s really sad to see puppies with congenital mega-oesophagus. In many cases, you'll need to euthanise them. The parents of puppies with congenital mega-oesophagus often do not show any visible abnormalities, which makes it difficult to select a breeding dog based on pedigree information. That made us hesitant to breed another litter. We wanted to do something for the health of the breed. We decided to take part in the screening programme at the Academic Veterinary Hospital and the research project at the Expertise Centre Genetics of Companion Animals in Utrecht.”
What did you learn from the screening?
“We used to believe the condition was quite clear-cut. As breeders, we only recognised pups with congenital mega-oesophagus and those that did not show any signs. The researchers discovered that the condition actually has different degrees of severity. In some cases, dogs without clinical symptoms also turned out to have impaired oesophageal function. That came as quite a shock, but it was definitely an eye-opener.”
How is this helping you as a breeder?
“Screening breeding animals’ oesophageal function with fluoroscopy allows more subtle abnormalities to be identified. That taught us that breeders should select on the basis of the primary trait rather than relying on pedigrees. That way, you do not need to exclude dogs from breeding unnecessarily, which is a good thing in terms of maintaining genetic diversity. We were surprised when one of our dogs turned out to have a perfectly functioning oesophagus, even though we assumed it would be genetically compromised on the basis of its pedigree.”
Have there been any tangible results yet?
"We get the screening results in the form of a colour-coded score. That makes it easier for us to mate dogs with weaker results with ones with good results when we breed. And screening all the puppies in a litter gives us insight into the variety of abnormalities. We keep the puppies with the best scores for breeding. Since we started screening our breeding dogs with fluoroscopy, we haven’t bred a single puppy with congenital megaoesophagus. That allowed us to lower the average score of our breeding stock quite quickly, even though we’re still breeding with the same lines.”
What are your hopes for the future?
“I hope more breeders will join the study so that we can breed healthier generations of white Swiss shepherd dogs in the future and identify the condition’s genetic causes. One breeder only has a limited influence on the breed as a whole. You can obviously achieve a much bigger impact if you work together.”