Snubbie Dogs: Breathing Easy!
Dogs, domesticated some 30,000 years ago, were the first animals to be domesticated by Man. The process of artificial selection—where people pick and choose certain phenotypical traits depending on what they want the dogs to be good at doing—has resulted in over 400 breeds of dogs to be recognized today. 400 different breeds of dogs has resulted in the dog family being the most morphologically diverse group of animals ever recorded. For example, Bloodhounds have been selectively bred for hundreds of years because of their keen noses, while German Shepards were bred for their intelligent minds. Along with this, the difference between the weights of one of the smallest and largest dog breeds—the Chihuahua and the Great Dane—is 145 pounds.
There are a plethora of specific traits people might breed for when breeding dogs; dog criteria can include coat color, size and shape of certain parts of the dog’s body, and many more. There have been great benefits from the artificial selection process for both animals and humans alike, but there have also been significant problems recorded. Diseases such as Von Willebrand’s disease in Dobermans, and physical ailments such as hip dysplasia in Labradors and breathing problems in brachycephalic (explained below) dogs are just a small list of the complications that artificial selection has caused dogs and dog owners to experience.
What does brachycephalic mean?
The veterinary medical literature has divided dog head length into three categories. Dolichocephalic (long headed), mesocephalic (medium headed) and brachycephalic (short headed). A dog is considered short headed when the cephalic (CI) index is greater than 60. This index is calculated by measuring the width of the head multiplied by 100 and then divided by the length, so a higher CI means a shorter head.
Initially, dogs were bred for shorter jaws, likely, because of the perceived increased bite strength, which might give them a potential advantage when fighting. Nowadays, the brachycephalic dogs are oftentimes selected because the higher forehead, bulging eyes and wider cheeks that mimics some of the facial characteristics of human infants. This likeness to human infants may evoke nurturing and other positive responses from their pet parents. The most common brachycephalic breeds are the French bulldog, pug, bulldog, Boston terrier and boxer, but other breeds also qualify. Just this month, the AKC announced that the French Bulldog is the most popular dog breed in the USA. Other brachycephalic breeds in the top 25 include the English Bulldog, Yorkshire Terrier, Chihuahua, Mastiff, Cane Corso, and the Shih Tzu.
With their increasing popularity, the brachycephalic (snub nosed) dogs have received every more scrutiny, due to some of the less desirable side effects of their head conformation. Secondarily there are some breeders and enthusiasts that think “more is better” as in more shortening of the nasal length, and more skin folds in breeds such as seen in chows and bull dogs. This mentality can exacerbate problems for the breeds.
The most common problem associated with snub nosed breeds is Brachycephalic obstructive airway syndrome (BOAS). This most common anatomical issues are a narrowing of the nasal openings (stenotic nares) and a smaller than typical windpipe (hypoplastic trachea). Genetically, snub nosed dogs have skeletal changes shortening the nasal area and jaws. However, the tongue and soft tissue don’t correspondingly shorten as much. This can lead to further issues for these dogs. Simply put, their skeletal structure becomes too small to house their teeth, soft palates, and tongues. These structural complications cause significant problems for the dogs’ breathing and associated temperature-regulation abilities. BOAS issues present, typically, in dogs 2-3 years of age and can lead to a myriad of breathing issues and tendency to overheat. With the increasing prevalence of snub-nosed dogs, more awareness of their associated issues is highlighted and the animal health community has responded with increasing welfare concerns. Many companies (and recently the British Veterinary Association) have even stopped using images of snub-nosed dogs in their ads for fear of a negative public perception. What steps can be taken to reduce issues and keep our snub-nosed friends safe from harm?
Supporting Responsible Breed Standards
Several years ago, German Shepherd enthusiasts sought to decrease the amount of hip dysplasia seen in the breed (and others will similar propensity). Examination of the causes of hip dysplasia were explored and changes instituted to help reduce the number of cases presented to veterinarians. These remedies included radiographic examination of breeding adults (genetic improvement) and dietary changes for puppies. By working on root issues, the incidence rate of hip dysplasia has fallen in many countries around the world.
The same approach needs to be taken for brachycephalic dogs. Recent data from the Royal Veterinary College in Cambridge UK has determined that 50% of BOAS variation (which includes pet weight, level of exercise, temperature and humidity) is environmental, and 50% is genetic. Obesity was cited as a major non-genetic contributing factor in developing BOAS.
The American Veterinary Medical Association has licensed the Respiratory Function Grading Scheme
(RFGS), which hopes to identify the dogs that are healthy, while segregating them out from dogs that have more severe cases. By identifying problem animals and fostering breeding only among healthy dogs, they hope to lower the prevalence of BOAS.
Additionally, a research article published in the Journal of Comparative Pathology stated that while some brachycephalic dogs show clinical signs of BOAS others do not suffer BOAS. So, by increasing the genetic diversity within the breeds (breeding more non-BOAS dogs) and finding the chief genetic markers of BOAS within dogs’ DNA code, we can potentially help dogs from being vulnerable to BOAS through thoughtful breeding practices.
The OFA (Orthopedic Foundation for Animals) in the US has instituted a pilot database which measures the extent of a dog’s nasal opening from digital photographs to better understand and predict predisposition of developing BOAS. A high degree of stenotic nares was found to be an important feature for predicting issues from BOAS. Generally, 1/3 of the width of the nose should be open to allow air to freely flow. If the opening is narrower, issues can arise.
Snub-nosed dogs are increasingly showing their popularity, and pet owners and breeders need to support them through better breeding, weight management, and understanding the environmental challenges they face. Breed extremes should be discouraged by dog show judges, which include too short muzzles and tight nares. Breeders should work with their veterinarians to select and reward moderation in morphology and use available testing/genetic screens. Only by a concerted effort by all interested parties will brachycephalic dogs enjoy better health and the breeds avoid the scrutiny that follows irresponsibility.
Written by Robert E. Devlin DVM. Dr. Devlin is veterinarian, animal health industry executive, and Snubbies
Advisory Board Member.