*1 May be under reported in Australia, as accurate reporting assumes follow up and/or testing. Many US breeders screen for a range of genetic conditions including autoimmune thyroid conditions and heart issues prior to breeding. The analysis of the 2006 Australian data stated the following “When considering the information provided, it must be accepted that conditions not seen prior to the pup leaving the breeder are likely to be under reported in this survey. These include heart murmurs, entropion, torsion/bloat, neurological problems, hip dysplasia, hypothyroidism, skin problems/allergies, cancers (including mast cell), elbow disease, and other skeletal issues.”
Inherited conditions fall into two main categories- those which require intervention and those that are mainly cosmetic, which generally mean the affected animals are sold as pets and de-sexed.
Inherited conditions requiring veterinary attention
Dermoid sinus
This is the inherited condition most commonly thought of in association with Ridgebacks. It is related to the formation of the ridge and similar to spina bifida in humans. It is generally detected at birth (by most breeders and some veterinary surgeons), and in this country most affected animals are euthanised (although in the US by 2000 only 52% were euthanised)2. The dermoid sinus is felt as a fine thread from the skin surface going down toward the vertebrae- and keep in mind some animals may have multiple sinuses. It is generally felt along the midline between the occiput bone and the beginning of the ridge, or from the end of the ridge and down into the tail. However, sinuses have been reported by some breeders as tracking through the epithelial surface and surfacing elsewhere such as on the cheek area. Left unchecked, epithelial cells may slough off into the sinus and cause the area to abscess.
An early paper on Dermoid sinus suggests inheritance is dominant with “inconstant penetration”4. A study has recently been published which determined the allele responsible for the ridge and demonstrated a link between dermoid sinus and the ridge5. They noted that in selectively breeding dogs with ridges together and removing ridgeless dogs from the breeding population, the genetic sequence that codes for both the ridge and dermoid sinus is over represented! Their findings are not surprising as my experience is such that where there are more ridgeless pups born (Rr parents), there is less dermoid sinus.
Hip Dysplasia
Most Ridgebacks in Australia and other countries are now X-rayed for hip dysplasia prior to breeding. Selective breeding in the US has reduced the incidence from 11.8% dysplastic dogs born prior to 1980 to 3.4% for dogs born in 2003/20046. Two main schemes are used in Australia for grading of hips- the British Veterinary Association (BVA) scheme, and more recently the PennHip scheme, with the BVA scheme being the most common. There are a number of views and articles on the relative value of each scheme7. In 2008 the BVA overall breed mean score for Ridgebacks is 118. The breed average in Australia is approx 6.7.
It is an uncommon but debilitating condition. In my experience some Ridgebacks are radiologically but not clinically dysplastic. However, the ideal is to chose breeding stock from those dogs with scores less than or around the breed mean score, while still keeping in mind the need to weigh up the quality of the whole animal when selecting breeding stock eg don’t throw away the baby with the bath water!
Gastric Dilation and Bloat
This is a life threatening condition, characteristic of large deep chested dogs and is sometimes seen in the Ridgeback. Early signs of this condition include attempts to vomit, restlessness, hunched up appearance and then a swelling abdomen9. One of the most comprehensive studies on this condition was undertaken by the Purdue University in the US and they concluded risks increased with:
- Increasing age
- Increased thorax depth/width ratio (eg more depth, less width)
- Having a first degree relative with a history of Bloat
- A faster speed of eating
- Using a raised food bowl10
Other studies have also implicated stomach tumours, a narrowed pylorus, eating non digestible foodstuff, stress and fear, eating only one meal a day, nasal mites (which contribute to air swallowing) and anything that delays gastric emptying9,11.
Elbow and Shoulder disease
The term “Elbow disease” covers a number of conditions such as ununited anconeal process (UAP), fragmented medial coronoid process (FCP) and osteochondrosis (OCD)12. Breeding stock are increasingly Xrayed for elbow dysplasia, although the low incidence of problems in this area have made this a recent phenomenon. Willis13 states that while there is breed predisposition for OCD, genetic overtones are uncertain. Recent work suggests elbow disease is inherited and animals with any evidence of elbow dysplasia (score of 1 or above) are breeding risks. This is a change in thinking from earlier days where dogs with scores 2 and above were regarded as breeding risks14. OFA figures from 2007 put elbow dysplasia in US Rhodesian Ridgebacks at 6.5%15.
Shoulder disease is more rarely reported, but OCD of the shoulder has been reported in the breed.
Eye problems:
Entropion (in-growing eyelids) is sometimes seen in the Ridgeback, and if early surgical correction is undertaken, rarely causes an on going problem. However, this is an inherited condition and affected animals should not be bred from. Cataracts, persistent papillary membranes, ectropion, corneal dystrophy and glaucoma have also been reported as inherited issues3.
Heart “murmurs”:
This term covers a number of clinical conditions. Cardiac conditions may be diagnosed by vets following detection of “heart murmurs”, which are caused by a variety of different cardiac problems. More specific diagnosis may need expensive diagnostic procedures to determine the cause and severity of the condition. The most common heart defects resulting in murmurs are patent ductus arteriosus (PDA-also seen in humans) and subaortic stenosis (SAS).
Other heart defects with an inherited basis seen in the breed include cardiomyopathy, persistent right aortic arch and pulmonary stenosis3. Some conditions can be detected by routine screening of pups prior to sale, but others such as SAS may not be found until later in life. It is not recommended to breed from animals with these conditions. It is also interesting to note that heart conditions are one of the few areas where numbers have increased between 1996 and 2006, and where the Australian numbers are higher than the US.
Thyroid problems and autoimmune disease:
Hypothyroidism is thought to be an inherited condition in the Ridgeback, and the US figures demonstrate a high prevalence in that country3. Comparative figures from other countries would be of interest, but few countries undertake this test as a routine screening procedure as yet! It can be hard to diagnose but signs may include incessant whining, nervousness, hyperactivity, failure to be attentive and unprovoked aggression16.
Hypothyroidism is generally a result of autoimmune disease which destroys the thyroid gland16. Other autoimmune diseases which have been reported in the breed include Addison’s disease, hyperadrenocorticism, autoimmune haemolytic anaemia, systemic lupus erythematosus (SLE) and degenerative myelopathy3. Autoimmune diseases are thought to have an inherited component, but some may not manifest without environmental triggers17
Hernias:
These have been reported in the breed, generally seen as umbilical hernias. Depending on severity they may need surgical correction. It is suggested the condition is inherited as a polygenetic theshold character13.
“Wobblers syndrome” (Spondololithesis):
This is sometimes seen in the rapidly growing young dog, and is seen in the Ridgeback. It is characterized by increasing “clumsiness” and loss of rear leg co-ordination and may result in paralysis1. Recent veterinary progress has offered new techniques for treatment of this condition.18 A genetic basis has been reported, and such animals should not be bred from13.
“Swimmers” (Pectus excavatum):
This condition is rarely seen and characterised by new born pups which seem “flattened” and incapable of standing. It appears to be inherited and culling is recommended.13
Monorchidism:
In some cases the one (or more rarely, both) testicles do not descend in the male pup. Breeders should check male pups carefully prior to sale as potential breeding animals, and ensure the desexing of dogs with one or no testicles. This is important as the retained testicle(s) may become malignant.
Chronic skin conditions:
Some Ridgebacks are prone to allergic dermatitis and some skin conditions have an inherited basis due to autoimmune disease1,13. Allergic dermatitis can be distressing for dog and owners, and in some lines it may be necessary to select against this condition.19 Systemic diseases such as hypothyroidism and Cushing’s Syndrome (hyperadrenalcorticism) can also manifest as skin conditions.20
Oncological Diseases (Cancer):
As with most animals (including humans), Ridgebacks are prone to cancer. I have lost older Ridgebacks with Osteosarcoma and Malignant Melanoma. The US figures suggest Mast Cell Tumours are prevalent in the breed and they have been reported in Australian Ridgebacks. Mast Cell Tumours are thought to have a genetic component, with some suggestion this also be the case for Osteosarcoma.21,3
Cosmetic inherited issues:
This is where we leave the realm of science and enter a more subjective arena.
The Ridge:
While this is the “escutcheon” of the breed, breeders have to contend with ridgeless pups, short ridges, animals born with offset (not parallel) crowns, or less or greater than two crowns. Many otherwise fine animals are sold as pets as their ridges are not suitable for the conformation ring. Breeders, and indeed judges, will vary in what degree of “offset” they will accept for the crowns, but should agree that animals with more (or less) than two crowns should not be bred from.
Structure:
As with any breed many structural faults appear to “run in families”. These may include poor fronts (lacking, or too wide), short muzzles, bad mouths, muzzles lacking in depth, “cheeky” heads, heads lacking in stop, high set ears, poor toplines, poor feet, steep croups or those lacking in slope resulting in high set tails etc etc. Also, as with other breeds, in many cases the worst of the structural defects are those which result in poor movement, with lesser defects more cosmetic in nature. Kinked tails, short and overlong tails are sometimes seen, and little has been done to look at the inheritance of these characteristics- although it is suggested kinked tails are inherited.
In my experience dental problems are associated with head structure eg lines with less depth of muzzle may see more overshot jaws, those with shorter and deeper muzzles are more likely to have issues with undershot jaws.
Coat Colour:
The breed standard calls for a light wheaten to red wheaten coat, with breeders sometimes debating what is too light or too dark. The standard of 1922 also allowed for brindles, sables “or mixed with white”, and excess white and black is sometimes still seen. Most breeders tend to judge these animals on their merits and an otherwise outstanding specimen with a long white sock or excess black will be bred with by some breeders, but perhaps not by others. Blue/Greys (either a Weimeraner type grey, or a blue/grey overlay on a red coat) and black and tan colourings are rarely seen in litters, and should not make the show ring or be bred from! The genetic recessive “brown nose” with a flesh coloured nose and light eye is quite acceptable in the breed and should be judged on conformation like any other Ridgeback.
Additional whorls in the coat:
In my experience these are not unusual and may be seen on the hindquarters, each side of the tail or on the neck below the ears. In some litters pups may also be born with whorls or crowns on the occiput area. They are also more rarely seen on the shoulders. Additional whorls on the top of the head or shoulders are usually penalised by breeders, whereas those on the hindquarter or sides of the neck are less likely to be seen as unacceptable.
Breeders responsibilities:
In cases of inherited conditions requiring veterinary intervention or severely affecting the health of the animal, the response of the breeder to finding an inherited condition should be clear cut. Do not breed from the affected animal and risk transmitting the condition to future generations. In the current age of litigation breeders should also be aware that knowingly breeding from faulty stock may result in puppy buyers successfully suing the breeder.
However, there are cases where the decision to breed from an animal is not so clear cut eg should an excellent specimen of the breed with a slight tail kink, too much black or white, or a crown on the head be removed from the breeding pool? I’m not proposing to answer this question, but only to remind breeders that they are the custodians of their breed, and must breed with care and knowledge of the genetic make up of their animals. It must be remembered that all our animals carry some genetic issues, so careful breeding must be done to minimise doubling up on any problems. Genetic information can only be obtained through the honesty of breeders with each other, and by screening of animals for breed related genetic defects prior to breeding.
The question of how much screening should be done is yet to be resolved. The following is taken from the Code of Ethics for members of the RR Club of the USA:
“Only dogs screened and certified clear of hip and elbow dysplasia by the Orthopedic Foundation for Animals, Pennhip or comparable foreign registry shall be bred. Other recommended genetic testing includes a complete thyroid panel* from an OFA-approved laboratory or canine endocrinologist, cardiac certification (OFA or cardiologist evaluation) CERF*(Canine Eye Registration Foundation) and BAER (Brainstem Auditory Evoked Response or hearing test). Breeders shall endeavor to stay current in their knowledge of all known inheritable diseases present in the breed and demonstrate reasonable care in eliminating those diseases (*indicates annual re-test requirement)”.
At present most Australian breeders are required by breed clubs to screen for hip and elbow dysplasia. If not in a breed club, there are no breeding requirements. Perhaps it is time to reconsider the level of testing undertaken to maintain the health of our breed, and to better inform our breeding selections? It is certainly time to be honest with each other for the betterment of our breed.
Vicki Moritz
Ujamaa Ridgebacks
July 2008
References: