International CEA Prevalence Data and Breeding Programme Success Stories

Collie Eye Anomaly does not respect borders. The NHEJ1 mutation exists in herding breed populations worldwide, from Scandinavian Rough Collie lines to Australian Shepherd populations in North America, from Shetland Sheepdogs in Japan to Border Collies in New Zealand. Yet CEA prevalence varies dramatically between countries and between breeding populations within the same country. Understanding these differences reveals which management strategies work, which fail, and what separates programmes that have achieved meaningful reduction from those that have stagnated. Over twenty-eight years of international consulting and collaborative research, I have gathered data and observations from breeding communities across four continents. What follows is my synthesis of where we stand globally and what we can learn from each other.

The Global Prevalence Picture

Estimating CEA prevalence accurately is challenging. Published figures depend on whether we measure carriers, affected dogs, or both; whether data comes from screened populations (introducing selection bias) or random samples; and how recently the data was collected. Nevertheless, the available evidence paints a clear picture of regional variation.

Several patterns emerge from this data. First, Rough Collie populations everywhere carry the mutation at high frequency, reflecting the breed's founding population genetics. Second, Scandinavian countries generally show lower prevalence than North America or the United Kingdom, a difference I attribute to earlier adoption of systematic screening and breeding guidelines. Third, prevalence in non-Collie breeds is uniformly lower but non-trivial, reinforcing the need for [tailored screening across all affected breeds including Australian Shepherds and Shetland Sheepdogs](/articles/cea-in-non-collie-breeds-australian-shepherds-shetland-sheepdogs/).

Success Story: Finland's Rough Collie Programme

I have written previously about the Finnish Rough Collie Club's CEA reduction programme, which I have had the privilege of consulting on since its early stages. It deserves detailed examination as perhaps the most successful documented effort to reduce CEA prevalence while maintaining genetic diversity.

Starting Point

When the programme began in 2009, approximately 85% of Finnish Rough Collies tested as carriers or affected. The breeding population was heavily saturated with the NHEJ1 mutation, and simply excluding all carriers was not a viable option. The club's genetics committee, advised by veterinary geneticists at the University of Helsinki and consulting ophthalmologists including myself, developed a phased approach.

Strategy

The programme rested on four pillars:

1. Universal testing: All breeding dogs required both genetic testing and clinical examination. Results were entered into the Finnish Kennel Club's open database, accessible to any breeder planning a mating.
2. Guided mating recommendations: The club recommended that affected dogs be bred only to clear partners. Carrier-to-carrier matings were discouraged but permitted when the dogs offered exceptional qualities unavailable in clear alternatives.
3. Retention incentives: Breeders were encouraged to retain clear puppies for future breeding through co-ownership arrangements and reduced registration fees for litters from recommended matings.
4. Education over enforcement: Breeders who deviated from recommendations faced no penalties but were required to test all offspring and disclose results publicly. The club invested heavily in breeder education seminars, which I participated in during 2010, 2014, and 2019.

Results

By 2015, the proportion of clear dogs in the tested population had risen from approximately 15% to 25%. By 2020, it reached 35%. The most recent data I have reviewed, covering dogs tested through late 2025, suggests the clear proportion now exceeds 40%. Importantly, the proportion of affected (homozygous) dogs has dropped from roughly 30% to under 12%. The programme also tracked [choroidal hypoplasia grading](/articles/choroidal-hypoplasia-grading-what-numbers-mean-breeding-program/) across generations, revealing a parallel shift toward milder clinical expression.

These numbers represent genuine population-level change achieved without crisis. Inbreeding coefficients in the Finnish Rough Collie population have remained stable or slightly improved during this period, and the breed's effective population size has not contracted. The programme has simultaneously reduced CEA prevalence and maintained genetic diversity; proof that these goals are not in conflict when the approach is thoughtful.

Success Story: Norway's Approach to Multiple Herding Breeds

Norway's approach differs from Finland's in its cross-breed coordination. The Norwegian Kennel Club, working with the country's veterinary ophthalmology community, implemented screening recommendations that apply across all affected herding breeds simultaneously rather than addressing each breed in isolation.

The Norwegian programme benefits from the country's relatively small and well-documented breeding populations. Most Norwegian Rough Collie breeders know each other and share information freely, a cultural factor that facilitates cooperation. The open health database maintained by the Norwegian Kennel Club includes CEA results alongside data on other hereditary conditions, enabling breeders to assess overall genetic health rather than focusing on single traits.

Norwegian Border Collie breeders have been particularly proactive. Despite relatively low CEA prevalence (estimated 3-5% carrier or affected), the breed community adopted routine NHEJ1 testing before their kennel club required it. This early adoption has kept prevalence stable and low, preventing the upward drift that can occur when carriers breed undetected in expanding populations.

Challenges: The United States

The situation in the United States presents different challenges. The Collie Club of America has long recommended eye examinations through the ACVO screening programme, and genetic testing has been widely available since OptiGen began offering commercial NHEJ1 testing. However, several factors complicate prevalence reduction.

First, the US Rough Collie population is large and geographically dispersed. Coordinating breeding recommendations across hundreds of breeders spread over a vast country is fundamentally harder than in Finland or Norway. Breed club guidelines exist but lack the enforcement mechanisms or social pressure that smaller, closer-knit communities can apply.

Second, the US breeding culture includes a significant population of casual or small-scale breeders who may not participate in breed club programmes. These breeders contribute meaningfully to the overall gene pool but may not test their dogs or follow screening recommendations. Their untested dogs introduce uncertainty into the population.

Third, the very high baseline prevalence in American Rough Collies (75-90% carrier or affected) means that even with optimised breeding strategies, progress is slow. When clear dogs constitute only 10-25% of the breeding population, finding suitable clear mates that also meet conformation, temperament, and other health criteria is genuinely difficult.

Despite these challenges, pockets of significant progress exist. Individual breeders and regional breeding cooperatives have achieved remarkable results within their own lines. I have worked with a Rough Collie breeding cooperative in the Pacific Northwest that pooled genetic data across seven kennels, coordinated stud access, and brought their combined clear rate from 18% to 45% over twelve years. Their success demonstrates that the Finnish model can work at smaller scales even within the US context.

The United Kingdom: A Mixed Picture

The United Kingdom occupies a middle ground between Scandinavian success and American challenges. The Kennel Club's breed health programmes have raised awareness of CEA, and the availability of testing through the KC's DNA testing service has reduced barriers. However, uptake remains inconsistent.

Rough Collie prevalence in the UK sits at an estimated 65-80% carrier or affected, lower than the US but higher than Scandinavia. The difference is partly attributable to early exchange of breeding stock with Scandinavian lines that introduced more clear genetics into UK populations. Several UK breeders have deliberately imported clear or carrier dogs from Finland and Sweden to improve their lines' CEA profiles, a strategy that simultaneously enhances genetic diversity.

Shetland Sheepdog breeders in the UK have been notably engaged with CEA screening. The relatively lower prevalence in Shelties (35-50%) means that clear-to-clear matings are achievable without extreme restriction of mate choice. Several UK Sheltie breeders have effectively eliminated CEA from their lines within three to four generations whilst maintaining strong breed type.

Continental Europe: Varied Approaches

Germany, France, and the Netherlands each take somewhat different approaches to CEA management, reflecting their distinct kennel club structures and breeding cultures.

Germany

The German Collie Club (Deutscher Collie Club) has among the most structured approaches in Continental Europe. Breeding dogs require both ophthalmoscopic examination and genetic testing, with results recorded in a centralised database. The club actively discourages affected-to-carrier matings and provides breeding advice through its genetics committee. German prevalence data shows gradual improvement, with clear rates rising from approximately 20% in 2010 to around 30% by 2024.

France

French Collie breeding has benefited from engaged breeders who have embraced genetic testing proactively. The French herding breed clubs have collaborated to share screening resources and information, recognising that the NHEJ1 mutation crosses breed boundaries. Notable French breeders have combined CEA screening with comprehensive health panels that address CEA severity alongside other hereditary conditions prevalent in their lines.

The Netherlands

Dutch Collie breeders work within one of Europe's more regulated kennel club frameworks. The Raad van Beheer has progressively tightened requirements for hereditary disease screening, and CEA testing is now effectively mandatory for registered breeding dogs. The Dutch approach demonstrates how institutional requirements can drive population improvement when voluntary compliance is insufficient.

Lessons from the Data

Examining international prevalence trends reveals several consistent lessons about what makes CEA reduction programmes succeed.

1. Open Data Drives Progress

Every successful programme I have studied features open, accessible health databases. When test results are public, breeders make better decisions, social accountability supplements formal rules, and population-level analysis becomes possible. Countries with confidential testing records consistently show slower improvement than those with open registries.

2. Education Outperforms Enforcement

Programmes built on breeder education and voluntary compliance have outperformed those relying on rigid rules and penalties. The Finnish model's success rests on breeders understanding why they are making certain choices, not on fear of sanctions. Educated breeders adapt guidelines to their specific circumstances more effectively than rigid protocols allow.

3. Gradual Selection Beats Abrupt Exclusion

No successful programme has achieved its results by banning carriers from breeding. Every programme that has tried abrupt exclusion has either failed (because breeders refused to comply) or caused unacceptable genetic diversity loss. Gradual selection, consistently applied over generations, produces sustainable improvement.

4. Cross-Breed Coordination Adds Value

Countries that address CEA across all affected breeds simultaneously benefit from shared infrastructure, shared knowledge, and the ability to track the mutation across breed boundaries. A carrier Sheltie bred from lines shared with Rough Collies carries the same mutation; managing it in isolation makes less sense than coordinated approaches.

5. International Gene Flow Is a Tool

Importing breeding stock from populations with lower CEA prevalence has accelerated progress in several countries. This requires careful attention to other health traits and breed type, but when done thoughtfully, it introduces clear genetics whilst simultaneously improving genetic diversity. The UK breeders who imported Scandinavian clear dogs benefited on both fronts.

Where We Need Improvement

Despite significant progress, several gaps remain in the global effort to reduce CEA prevalence.

Comprehensive prevalence data from Asia, South America, and parts of Eastern Europe remains sparse. Japan has a meaningful Shetland Sheepdog population with documented CEA, but data from other Asian countries is limited. South American herding breed populations are growing but largely unscreened. Without baseline data, targeted reduction programmes cannot be designed.

Testing compliance in casual breeding populations worldwide remains low. Professional breeders who show and register their dogs are increasingly likely to test, but the broader population of dog breeders includes many who do not participate in kennel club programmes. Reaching these breeders with affordable, accessible testing is an ongoing challenge.

Integration of CEA data with other hereditary eye condition databases would benefit both research and breeding decisions. A breeder evaluating a potential mate should be able to review CEA status alongside progressive retinal atrophy results, hereditary cataract status, and other relevant findings in a single location. Some databases approach this goal, but fragmentation remains common.

A Vision for the Next Decade

Based on current trends and the tools available, I believe it is realistic to expect that well-managed Rough Collie populations in Scandinavia will reach 60-70% clear status within the next decade. UK and Continental European populations should approach 40-50% clear. US populations, if cooperative breeding efforts expand, could reach 30-40% clear in their engaged subpopulations.

For Shetland Sheepdogs, some populations are already approaching effective elimination of CEA. UK and Scandinavian Sheltie breeders who have consistently bred clear-to-clear for several generations have lines with near-zero affected rates. Extending this success to the broader population requires continued education and testing access.

For Australian Shepherds and Border Collies, the goal should be maintaining low prevalence and preventing upward drift. With current testing tools, there is no reason for CEA prevalence to increase in these breeds. Routine inclusion of NHEJ1 testing in standard health panels keeps the mutation visible and manageable.

The international community of CEA researchers, ophthalmologists, and dedicated breeders has accomplished extraordinary things since the causative mutation was identified in 2007. Less than twenty years of informed selection has already changed population genetics measurably. With continued commitment, collaboration, and the tools of modern genetics, the next twenty years should bring changes that would have seemed impossible when I first peered through an ophthalmoscope at a Collie's fundus nearly three decades ago.

The data tells us what works. The success stories show us it is achievable. What remains is the collective will to apply these lessons consistently, across borders and across breeds, until Collie Eye Anomaly is a manageable rarity rather than a common burden. For guidance on implementing these strategies with your own dogs, the principles of evidence-based breeding selection apply regardless of which country you breed in.