THE first reliable data on the incidence and impact of inherited diseases in pedigree dogs should prove to be the lasting legacy of a controversial BBC documentary which focused public attention on the unwelcome effects of selective breeding.
Although health problems in particular breeds have been recognised for decades, there were remarkably few co-ordinated studies on the health and welfare issues caused by inherited disease until Pedigree Dogs Exposed was screened in August last year.
Despite accusations of sensationalism from canine organisations, the programme has since provided the impetus for the first systematic attempts in Britain to remedy those faults, involving veterinary scientists, welfare organisations and many breeders.
The results of two important studies were described at a symposium organised by the Universities Federation for Animal Welfare at the University of Bristol on 22nd and 23rd June. The meeting on Darwinian selection, selective breeding and the welfare of animals was organised as part of the 200th anniversary celebrations of the birth of the great Victorian biologist.
No doubt Charles Darwin would have been interested in the findings, as he had pondered the effects of selective breeding on canine health in his 1868 book, The variation of plants and animals under domestication. In it, he suggested that muscle diseases in the Scottish deerhound were a consequence of breeding for excessive size, noted Lisa Colins, an epidemiologist at the Royal Veterinary College.
Potential strategies
Dr Collins described a Dogs Trustfunded study assessing the impact of inherited diseases, based on the combination of the prevalence within the affected breed and the severity of the effects on the individual animal. Nicola Rooney of Bristol University outlined progress in a collaboration with the Cambridge veterinary school and the RSPCA investigating potential strategies for eliminating such disorders.
Dr Rooney noted that most papers in the veterinary literature on inherited diseases deal with methods for surgically or medically correcting the disorder rather than assessing their effects on animal welfare. However, it was clear that breeding for appearance alone has severely compromised the welfare of many breeds, through both the direct effects of exaggerated anatomies and the indirect effect of genetic diseases.
Dogs of brachycephalic breeds such as bulldogs and pugs will typically die more than two years before dogs of equivalent size with a more natural facial conformation. Quality of life was also affected with many giant-breed dogs suffering discomfort in their latter years as a result of inherited bone, cardiac and digestive conditions.
Also, the effects of congenital diseases on behaviour should not be underestimated, since dogs with distorted faces are less able to convey standard canine signals and so are less likely to enjoy normal social interactions, she said.
The Dogs Trust study gathered information from published sources, including three established databases on inherited defects produced by the Cambridge veterinary school and institutions in Canada and Australia. From this they developed a method of objectively examining the effects of disorders in the 50 most popular of the 209 Kennel Club registered breeds.
Assigning scores for the prognosis, treatment, complications and effects on behaviour allowed the team to construct the Generic Illness Severity Index for Dogs (GISID) to compare the disease burden in different breeds.
This revealed a total of 521 separate diseases in those breeds, including 63 conditions that were directly and 21 indirectly related to the breed conformation. “Every single one of the 50 breeds was predisposed to at least one inherited disorder that was conformation linked,” Dr Collins noted.
The German shepherd dog is the breed with the most recognised problems with a total of 69 conditions, followed by the miniature poodle and the boxer. But when assessed on severity, the miniature poodle ranks highest as the result of the effects on its health and welfare of its 55 inherited conditions, including 17 resulting from its conformation.
Other breeds with smaller numbers of problems but which have particularly deleterious effects include the English springer spaniel and toy poodle, and perhaps more predictably the bulldog, basset hound and pug.
In many cases diseases have been directly selected for by the wording of the breed standard – deafness in Dalmatians and spina bifida in pugs are both directly linked to particular desired traits for those breeds, Dr Collins said.
She welcomed the recent willingness of breed societies to accept the need for revised breed standards, led by the Pekingese breeders club. This should help to eliminate some of the health problems that were present in the 2003 Supreme Champion “Danny”, which had to sit on an ice pack to avoid overheating under the TV camera lights.
Dr Rooney’s project has canvassed opinions from 20 leading authorities on inherited disorders in pedigree dogs on the measures that would have the most significant effects on the dogs’ health and welfare. Paramount among these would be efforts to set up a system for continually gathering accurate data on morbidity and mortality in registered pedigree dogs and to monitor the effects of changing practices.
Another important step would be to preserve genetic diversity by refusing to register the offspring of second degree mating such as those between a young dog and its grandparent, or between two half siblings. She said the Kennel Club has already acted to stop matings between first degree relatives but those were actually much less common than the second degree matings, which account for about 5% of all pedigree registrations.
Further necessary measures would be to open up the closed stud books of the affected breeds to allow the input of healthy stock from closely related breeds, and efforts to encourage the importation of new bloodlines from abroad.
These changes would be a challenge to traditional breeding practices but have been shown to be effective in the past as when Dalmatians in the US were mated with pointers and back crossed to produce the Dalmatian phenotype but without a propensity for developing bladder stones.
For this approach to become more widespread, however, there would have to be changes in the rules on the registration of these puppies: if breeders have to back cross for several generations before the pedigree is accepted, then that will be a significant financial disincentive, she said.
Currently there are three major health screening programmes run by the BVA, Kennel Club and other bodies and DNA tests for about 50 inherited disorders. Only in two breeds and a single disorder is compulsory testing of both sire and dam required before puppies can be registered and so testing should be made compulsory for both parents.
Dr Rooney said it was not acceptable for the 700 or so independent breed clubs and societies to continue operating completely autonomously. To achieve any progress it was vital that there should be cooperation between the various interest groups. Dog breeders would also have to accept guidance from outside experts.
“Those immersed in the discipline have preconceived ideas about what is normal and acceptable and so it is really important to have external input.”
She proposed that there should also be ethical reviews to assess the quality of life of the affected breeds. These may result in proposals for a programme of rapid outcrossing or even the phasing out of those breeds considered to be so genetically impoverished as to be beyond rescue.
Tom Lewis of the Kennel Club Genetics Centre at the Animal Health Trust described the early stages of a project to develop estimated breeding values for companion animals.
This concept is well-established in livestock breeding, where it is a statistical measure of the heritability of desired characteristics, adjusted for the known effects of environmental factors. This offers a much more reliable method of breeding for healthy offspring than relying solely on the phenotype expressed through the mating.
The eventual aim would be to set up a website for the owners of dogs and bitches intended for breeding which would help them to select a mate with a genetic inheritance that will ensure healthy puppies.
Dr Collins agreed that expert advice from geneticists will be vital in remedying the problems caused by uncontrolled selective breeding for appearance. As the available gene pool for most breeds was so small, it would be very easy for breeders to work towards removing one breed disorder only to find that they have created another problem to take its place.
