PRA in Collies, Australian Shepherds, and Herding Breeds

The Border Collie named Fleet could work sheep with an intensity that made experienced handlers pause in admiration. At seven years old, she began missing visual cues from her handler, subtle hand signals that had once triggered instant responses. Her owner initially attributed the changes to selective hearing, a common joke among herding dog owners. When Fleet bumped into a gate she had navigated thousands of times, the joke stopped being funny.

Fleet's diagnosis with Progressive Retinal Atrophy represented more than personal tragedy for her owner. It raised questions about the entire breeding program behind her. How had a dog from tested parents developed PRA? The answer lay in the complexity of PRA genetics in herding breeds, a topic that demands careful attention from anyone breeding or owning these remarkable dogs.

The Herding Breed PRA Landscape

Herding breeds do not share a single PRA mutation. Instead, different breeds carry different variants, each with distinct characteristics and testing requirements. This diversity reflects the independent development of these breeds across different regions and time periods.

Collies: The rcd2 Challenge

Rough and Smooth Collies share the rcd2 mutation, one of the earliest-onset and most severe PRA forms. Affected puppies show abnormal photoreceptor development from birth, with clinical blindness typically occurring by one to two years of age. The mutation affects the PDE6B gene, encoding a critical enzyme in the phototransduction cascade.

The early onset of rcd2 presents both challenges and opportunities. The challenge lies in the rapidity of disease progression, leaving little window for potential intervention. The opportunity emerges from the ability to identify affected puppies before they would typically be placed in breeding programs, assuming breeders test appropriately.

Australian Shepherds: prcd and Beyond

Australian Shepherds carry the PRCD mutation, the same variant affecting numerous other breeds including Labrador Retrievers and Cocker Spaniels. This represents the most widespread PRA mutation in dogs, likely arising thousands of years ago before breed differentiation.

The prcd form causes later-onset disease than the Collie variant. Australian Shepherds typically show first clinical signs between ages three and five, with gradual progression over several years. This timeline means affected dogs may reproduce before showing symptoms unless DNA testing identifies their status.

In my ophthalmology practice, I see Australian Shepherds at various disease stages. The working dogs often present earlier because owners notice subtle performance changes, a slight hesitation in low-light gathering or difficulty tracking sheep at dusk. Pet owners may not recognize problems until more advanced disease develops.

Cardigan Welsh Corgis: Rapid Progression

The Cardigan Welsh Corgi faces rcd3, a particularly aggressive PRA form. Affected puppies show electroretinographic abnormalities as early as six weeks of age, with clinical blindness often occurring by one year. The mutation disrupts the PDE6A gene, the alpha subunit partner to the beta subunit affected in Collie rcd2.

Cardigan breeders have made remarkable progress in reducing rcd3 frequency through systematic testing and strategic carrier management. The breed community's commitment to transparency about test results has enabled rapid improvement while maintaining genetic diversity.

Border Collies: An Emerging Picture

Border Collies present the most complex PRA situation among herding breeds. Multiple PRA forms appear to exist in the breed, not all with identified causative mutations. This creates frustration for breeders who test their dogs yet still occasionally produce affected offspring.

Recent research has identified several candidate genes, but commercial tests do not yet exist for all Border Collie PRA variants. Breeders should test for known variants while also maintaining annual ophthalmologic examinations by board-certified veterinary ophthalmologists to detect clinical PRA that current DNA tests might miss.

The Working Dog Dimension

PRA carries particular significance for herding breeds because vision is integral to their work. A blind or vision-impaired herding dog loses the ability to perform the tasks that define their purpose. This reality drives the urgency of PRA prevention in these breeds.

Fleet, the Border Collie from the opening story, adapted to vision loss with remarkable resilience. Her owner transitioned her from competitive herding to companion status, and she lived happily for several more years. But the story represents a preventable outcome. With proper testing of her parents for all known variants plus clinical screening, her affected status might have been predicted or avoided entirely.

Implementing Effective Prevention

For herding breed breeders, effective PRA prevention requires a multi-layered approach:

1. Identify breed-specific variants: Determine which PRA mutations affect your breed specifically. Testing for the wrong variant wastes resources and provides false reassurance.
2. Test all breeding stock: DNA testing before first breeding should be mandatory. Results guide mate selection and prevent carrier-to-carrier breedings.
3. Maintain clinical screening: Annual ophthalmologic examinations catch PRA forms without available DNA tests. This is especially important for breeds like Border Collies with incompletely characterized genetics.
4. Share results openly: Breed health databases only work when breeders participate. Transparency enables informed mate selection across the breed community.
5. Use carriers strategically: Carriers bred to clear dogs produce zero affected offspring. Eliminating all carriers too quickly damages genetic diversity.

The Broader Context

PRA represents just one inherited condition affecting herding breeds. Collies face Collie Eye Anomaly, Australian Shepherds carry risks for MDR1 drug sensitivity and hereditary cataracts, and Border Collies navigate trapped neutrophil syndrome and other concerns. The Herding Gene resource provides comprehensive information on inherited conditions across herding breeds.

Responsible breeding requires attention to the complete health profile, not just single conditions. A dog clear for PRA but affected by other serious conditions does not represent a breeding improvement. Comprehensive health testing, combined with thoughtful mate selection considering the whole dog, moves breeds toward genuine health improvement.

Hope Through Gene Therapy

Gene therapy research offers long-term hope for PRA-affected dogs. While current approved treatments target other variants, the success of these approaches demonstrates the principle that vision restoration is possible. Research on gene therapy for prcd and other common variants continues, potentially offering future options for herding breeds.

Until such treatments become widely available, prevention remains the most practical approach. The DNA tests exist. The knowledge of inheritance patterns is well-established. The genetic basis of each variant is documented. What remains is the collective decision by herding breed communities to use these tools consistently and transparently.

The herding breeds that have made the most progress against PRA share common characteristics: strong breed club commitment to health testing, open databases for sharing results, and education programs that help breeders understand the genetics involved. These approaches work. They can work for every herding breed willing to embrace them.

Dr. Amanda Foster, Veterinary Ophthalmologist