The Rhodesian Ridgeback is defined by a strip of backwards-growing hair. The genetics behind it are more contested than anyone likes to admit
Every breed standard describes a dog, but the Rhodesian Ridgeback standard does something less usual: it disqualifies any dog that does not carry the breed’s single defining feature. Under the current FCI standard, published in May 2025 and supplied by the Kennel Union of Southern Africa and the Zimbabwe Kennel Club, a dog without a ridge cannot be shown. The ridge, in the standard’s own phrase, is the escutcheon of the breed.
However, that same ridge has been linked for decades to a congenital defect called dermoid sinus. Understanding what that link actually is, and what it is not, as well as its significance for the future, turns out to be considerably harder than most writing on the breed suggests.
Origins
The FCI standard traces the breed’s forebears to the Cape Colony, where the dogs of early European settlers crossed with the semi-domesticated ridged hunting dogs kept by the Khoikhoi. The original standard was drafted by F.R. Barnes in Bulawayo in 1922, modelled on the Dalmatian standard, and approved by the South African Kennel Union in 1926.
This makes the geography reasonably layered. The ancestry is Cape, the standardisation was Zimbabwean, and the recognition was South African. The FCI describes the Ridgeback as the only registered breed indigenous to southern Africa.
What the standard asks for
The ridge must be clearly defined, symmetrical and tapering towards the haunch. It must begin immediately behind the shoulders and run to the hip bones. It must contain exactly two crowns, identical and opposite one another, and the lower edges of those crowns must not extend further down the ridge than one third of its length. A good average width for the ridge is given as five centimetres.
Incorrect crowns are listed as a fault. A lack of the ridge is listed as a disqualifying fault, along with other faults including aggression, extreme shyness, and any clear physical or behavioural abnormalities.
So, a ridgeless Ridgeback, which is a structurally normal dog, sits in the same category as a dog with a physical abnormality or behavioural issue. The standard also closes with a note that only functionally and clinically healthy dogs with breed-typical conformation should be used for breeding. Those two requirements are in tension, and the rest of this piece is about that tension.
The ridge
Dermoid sinus is a congenital malformation. It arises during development if the skin fails to separate cleanly from the neural tube. This leaves a tube-like tract running inwards from the skin of the midline. Some of these tracts are shallow, but some connect to the spinal cord. These tracts can become infected, and infection there can cause pain, neurological signs, and in some cases death. The only available treatment is surgery.
In 2006, Swedish researchers established that the ridge is inherited as an autosomal dominant trait, and reported that the trait predisposes to dermoid sinus (Salmon Hillbertz and Andersson, Journal of Small Animal Practice, 2006). The following year, the same group identified the mutation itself: a 133 kilobase duplication on chromosome 18 involving the fibroblast growth factor genes FGF3, FGF4 and FGF19, along with ORAOV1 (Salmon Hillbertz et al., Nature Genetics, 2007).
The proposed model was elegant and widely adopted. One copy of the duplication gives you a ridge and a low risk of dermoid sinus. Two copies give you a ridge indistinguishable from the first and a substantially higher risk of dermoid sinus. On that model, the breed’s signature is inseparable from its signature defect, and breeding two homozygous dogs (dogs with two copies of the duplication) together is the thing to avoid as it would be assumed to increase the risk of puppies with dermoid sinus.
This model is the one repeated in almost every breed article, on most breeder websites, and in the marketing for commercial ridge copy-number DNA tests, even today. However, the recent literature has complicated the model.
Recent evidence
Two 2022 papers from the University of Veterinary Medicine Hannover are the reason for caution in accepting the previous model.
The first paper analysed 12,700 puppies from 1622 litters born in Germany between 2001 and 2019 (Distl, The Veterinary Journal, 2022). Overall prevalence of dermoid sinus in the puppies was 2.53%. In the 1269 litters containing only ridged animals, it was 2.81%. In 46 litters, ridgeless dogs appeared, and two of those ridgeless dogs had dermoid sinus.
This last detail is significant because the earlier Swedish work had found no affected ridgeless individuals at all. Heritability came out at 0.78, which is high, but a simple single-gene recessive model did not fit the data. The genetic correlation with ridgelessness was only minus 0.11. Ultimately, the paper concluded that the ridge locus was unlikely to determine whether a dog develops dermoid sinus.
The second paper, published the same year, addressed the question directly and concluded that the duplication responsible for the hair ridge is not identical to the hypothesised gene locus for dermoid sinus (Zhang and Distl, Animal Genetics, 2022).
Prevalence estimates across the literature vary widely, from figures around 2.5% in the recent German data to considerably higher numbers reported in earlier Swedish work. Populations, eras and methods of ascertainment all differ, so the honest position is that we do not have a single reliable prevalence figure for the breed, and certainly not one for South Africa.
However, the bottom line seems to be that the ridge gene is not the gene solely responsible for dermoid sinus.
Where the evidence now stands
• The ridge is caused by a 133 kilobase duplication on chromosome 18. This is well established and not in dispute.
• The ridge and dermoid sinus occur together in this breed far more than chance would predict. This is also not disputed.
• Whether the ridge duplication itself determines dermoid sinus is now contested. Recent work says probably not, and points to a more complex genetic basis.
• Dermoid sinus has been recorded in ridgeless dogs, which the original model did not predict.
• German data show the prevalence of dermoid sinus falling year on year.
What this means for DNA testing
Ridge copy-number tests are real, validated and useful for what they measure. They tell you whether a dog carries one copy of the duplication or two, which cannot be determined by looking at the dog, since one copy and two copies produce the same ridge.
What is less certain is what that result now predicts. If the duplication is not the locus driving dermoid sinus, then knowing a dog’s ridge copy number tells you less about its puppies’ risk of dermoid sinus than the test’s framing implies. This is not a reason to skip testing, certainly at this stage in the research process. However, it is a reason to be sceptical of anyone who presents a copy-number result as a guarantee, in either direction.
The rest of the health picture
Outside of the potential ridge and dermoid sinus issue, the breed is reasonably healthy with just a few exceptions.
Firstly, the Ridgeback has its own form of juvenile myoclonic epilepsy, caused by a recessive variant in the DIRAS1 gene and described in 2017 (Wielaender et al., PNAS). Onset is early, from about six weeks to eighteen months, averaging around six months. The characteristic sign is myoclonic jerking that occurs mainly when the dog is relaxed, drowsy or falling asleep, rather than during activity. Roughly a third of affected dogs also develop generalised tonic-clonic seizures. The variant is recessive and fully penetrant, which means a DNA test is genuinely informative here, and two clear parents cannot produce an affected puppy.
Beyond that, the breed’s testing panel covers ground familiar to any large, deep-chested working dog: hip and elbow dysplasia; thyroid disease; degenerative myelopathy, for which an SOD1 test exists; and gastric dilatation and volvulus, which is an emergency and is a conformational risk rather than a genetic one.
Finally, spinal anatomy is also worth considering. A 2025 German study of Ridgeback radiographs from 2012 dogs found lumbosacral transitional vertebrae in 7.4% of dogs, and found no statistically significant association with hip dysplasia (Slunsky et al., Veterinarni Medicina, 2025).
Lifespan figures for the breed are widely quoted at around ten to twelve years, but we could not locate a strong breed-specific primary source for that range, and readers should treat it as a rule of thumb rather than a finding.
The difficult question
Ridgeless puppies are born into most Ridgeback litters at a low but persistent rate. Swedish work put ridgeless dogs at roughly 5.6% of that country’s population. These dogs are healthy but they are not showable, and for this reason, historically, many were culled at birth.
This was not an informal practice; rather, it was documented. The Rhodesian Ridgeback Club of Great Britain’s code of ethics stated that ridgeless puppies shall be culled, a clause raised publicly by the BBC documentary Pedigree Dogs Exposed. The club’s defence at the time pointed to the following sentence, which allowed a breeder who found culling morally impossible to home the puppy instead. They argued that this made culling preferred rather than mandatory.
The direction of travel since then has been clear (and better!). The Rhodesian Ridgeback World Congress meeting in Sweden in 2016 resolved to encourage breed clubs to remove punitive language from codes of ethics regarding healthy dogs with cosmetic faults only. Club codes have been rewritten, and the current code of the Rhodesian Ridgeback Club of the United States requires that puppies with dermoid sinus or ridgelessness be sterilised when sold. The Rhodesian Ridgeback Club of Victoria’s code now commits to desexing ridgeless puppies rather than culling them.
That is real progress. However, what has not changed is the disqualifying fault in the standard, which is the pressure that produced the practice of culling in the first place.
Living with a Ridgeback
The standard asks for a dog that is dignified, intelligent and aloof with strangers, showing neither aggression nor shyness. Males stand 63 to 69 centimetres at the withers, females 61 to 66, with reference weights of 36.5 and 32 kilograms. The coat is short, dense and glossy, light wheaten to red wheaten.
Aloof is the operative word, and it is often misread. A Ridgeback that ignores your visitors is doing what the standard asks. A Ridgeback that lunges at them is not, and neither is one that cowers. Both aggression and shyness are faults under the standard, and both are worth raising with a breeder rather than explaining away as breed character.
This is a dog bred to work at pace over distance and to hold large game at bay until a hunter arrived. That history produces independence, a considerable prey drive, and a physical need that a suburban garden does not meet.
What to ask a breeder
• Have both parents been hip and elbow scored, and may I see the certificates rather than a verbal assurance?
• Have both parents been DNA tested for juvenile myoclonic epilepsy? This one is recessive and fully penetrant, so the answer should be unambiguous.
• Has every puppy in the litter been checked for dermoid sinus, and by whom?
• What happens to ridgeless puppies born here? The answer, and the manner of the answer, tells you a great deal about the breeder.
• Are the parents ridge copy-number tested, and how do you use that result? A breeder who treats it as one input among several is being more honest than one who treats it as a guarantee.
The verdict
The Rhodesian Ridgeback is a sound, athletic, strikingly good dog with a smaller catalogue of inherited disease than many breeds of comparable size and popularity.
However, the honest summary of the genetics is not the tidy one on either side. The ridge is not a proven cause of dermoid sinus, and anyone telling you it is has not read the last four years of literature. However, the association is also not imaginary, and anyone telling you that has not read the twenty years before it. The two travel together in this breed for reasons that are not yet fully understood, but in good news, the prevalence is falling.
What remains difficult, in our view, is a standard that treats the absence of a cosmetic trait as a disqualification in a breed where that trait sits close to a congenital defect, while simultaneously asking that only functionally and clinically healthy dogs be bred. The science will hopefully give us a definitive answer to the dermoid sinus question one day, but an update to the breed standard is what we’re far more interested in.
References
FCI Standard No. 146, Rhodesian Ridgeback, official valid standard published 15 May 2025, supplied by the Kennel Union of Southern Africa and the Zimbabwe Kennel Club. • Salmon Hillbertz NHC and Andersson G. Autosomal dominant mutation causing the dorsal ridge predisposes for dermoid sinus in Rhodesian ridgeback dogs. Journal of Small Animal Practice, 2006; 47: 184 to 188. • Salmon Hillbertz NHC et al. Duplication of FGF3, FGF4, FGF19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus in Ridgeback dogs. Nature Genetics, 2007; 39: 1318 to 1320. • Distl O. Prevalence and segregation analysis of dermoid sinus in Rhodesian Ridgebacks. The Veterinary Journal, 2022; 280: 105803. • Zhang X and Distl O. A study of Rhodesian Ridgeback dogs indicates that the duplication responsible for hair ridge is not identical with the hypothesized locus for dermoid sinus. Animal Genetics, 2022; 53: 231 to 233. • Wielaender F et al. Generalized myoclonic epilepsy with photosensitivity in juvenile dogs caused by a defective DIRAS family GTPase 1. PNAS, 2017; 114: 2669 to 2674. • Slunsky SK et al. Prevalence of lumbosacral transitional vertebrae and association with hip dysplasia in Rhodesian Ridgebacks in Germany. Veterinarni Medicina, 2025.
