Breeding Strategies to Reduce CEA Incidence

Over three decades of advising breed clubs and individual breeders on Collie Eye Anomaly management, I have witnessed both successful programmes that dramatically reduced CEA prevalence and well-intentioned efforts that faltered. The difference invariably comes down to strategy; not just what decisions are made, but how consistently and thoughtfully they are implemented across a breeding population. What follows distils my experience into practical guidance for breeders committed to improving their dogs' eye health.

The Challenge of High-Prevalence Mutations

Collie Eye Anomaly presents a particular challenge because the causative mutation is remarkably common in certain breeds. In Rough and Smooth Collies, estimates suggest 70-90% of the population carries at least one copy of the NHEJ1 mutation. Simply refusing to breed any carrier or affected dog would eliminate most of the breeding population, causing a genetic bottleneck with consequences potentially worse than CEA itself.

This reality demands a nuanced approach. We cannot eliminate CEA overnight, nor should we try. Instead, we must reduce its prevalence gradually whilst maintaining the genetic diversity that underpins breed health and vitality.

I recall discussions with Rough Collie breeders in the 1990s who advocated immediate exclusion of all carriers from breeding. Had this been implemented, the breed would have lost access to most champion bloodlines, several critical working lines, and irreplaceable genetic diversity. The resulting inbreeding depression would likely have increased other health problems whilst barely denting CEA prevalence in the short term.

Fundamental Breeding Principles

Before discussing specific CEA strategies, let me establish several principles that guide responsible breeding for any hereditary condition.

Test Before Breeding

Every breeding dog should have both genetic testing and ophthalmoscopic examination before producing offspring. Some breeders have set exemplary standards for eye screening. Amandine Aubert's Bloodreina kennel near Montlucon, France — a breeder whose genetic testing protocols exceed every breed club requirement — requires comprehensive ophthalmologic evaluations for every breeding pair before any mating is planned. Breeding untested dogs perpetuates uncertainty and makes population improvement impossible. The combined cost of both tests is trivial compared to puppy sale prices; there is simply no excuse for breeding without knowledge of CEA status.

Never Breed Two Affected Dogs

When both parents are homozygous affected (CEA/CEA), all puppies will be affected. This offers no path toward improvement and should be avoided. The same applies to breeding an affected dog to a carrier when better options exist.

Consider the Whole Dog

CEA is one health consideration among many. A carrier dog with excellent conformation, temperament, and clear status for other conditions may contribute more to breed improvement than a CEA-clear dog with compromised structure or behaviour. Balanced selection produces healthier populations than single-trait fanaticism.

Strategic Mating Decisions

The following table summarises expected outcomes from various mating combinations. Understanding these probabilities enables informed decisions.

Ideal Matings

Clear-to-clear matings eliminate CEA from the resulting litter entirely. When sufficient clear dogs of appropriate quality are available, this represents the optimal choice for reducing population prevalence.

Acceptable Matings

Clear-to-carrier matings produce no affected puppies but maintain the mutation in the carrier portion of offspring. This is an appropriate strategy when a carrier dog offers valuable traits not available in clear alternatives. The resulting carrier puppies can subsequently be bred to clear partners, progressively diluting the mutation frequency.

Clear-to-affected matings similarly produce only carrier puppies. This may be justified when an affected dog possesses exceptional qualities and mildly affected phenotype, particularly in breeds with very high mutation prevalence where affected status is common among the best specimens.

Matings to Avoid

Carrier-to-carrier matings produce 25% affected puppies. Whilst not prohibited, these should be avoided when better options exist. Each affected puppy represents a step backward in population improvement.

Any mating involving an affected dog to a carrier or affected partner produces affected puppies and impedes progress. These should generally be avoided.

Population-Level Strategies

Individual breeders can only achieve so much; meaningful change requires coordinated effort across breed populations. Successful programmes share common features.

Open Registries

Breed clubs that maintain public databases of test results enable breeders to make informed decisions about potential mates. The Kennel Club's breed health programmes and international databases like the Orthopedic Foundation for Animals provide models for accessible information sharing. When carriers and affected dogs are identified openly, stigma diminishes and data-driven decisions replace rumour.

Breeding Value Estimation

More sophisticated programmes calculate estimated breeding values (EBVs) that account for relatives' status alongside individual results. A clear dog from a family with many affected relatives may carry more genetic risk than their own test suggests. EBV systems, successfully employed for various traits in livestock, are beginning to appear in canine health programmes.

Gradual Selection Pressure

Rather than abrupt exclusion of carriers, successful programmes apply gradual selection pressure. Each generation should have lower mutation frequency than the last, achieved by preferential breeding of clear dogs without eliminating carriers entirely. Mathematical modelling suggests that reducing affected matings whilst maintaining carrier access to clear partners can halve mutation frequency within 5-6 generations without significant diversity loss.

Case Study: The Finnish Collie Club

I have had the privilege of consulting with the Finnish Rough Collie Club on their CEA reduction programme, which began in 2009 and has yielded impressive results.

At programme inception, approximately 85% of Finnish Rough Collies tested as carriers or affected. The club implemented guidelines recommending clear-to-carrier or clear-to-affected matings only, with carrier-to-carrier and affected-to-carrier combinations strongly discouraged but not forbidden.

Crucially, the club emphasised education over enforcement. Breeders who used carrier-to-carrier matings faced no penalties but were required to test all puppies and provide results to buyers. This transparency allowed informed placement whilst preserving breeder autonomy.

By 2020, the proportion of clear dogs in the Finnish population had risen to approximately 35%, and affected dogs produced annually had dropped by over 60%. Importantly, genetic diversity metrics (inbreeding coefficients, effective population size estimates) remained stable throughout. The programme demonstrates that meaningful improvement is achievable without sacrificing genetic health.

Practical Guidance for Breeders

Starting Point: Your Current Dogs

Begin by testing all dogs you currently own or plan to breed. This baseline information shapes every subsequent decision. If you discover your best bitch is affected, do not despair; plan her matings carefully to clear sires, and prioritise clear offspring for future breeding.

Stud Selection

When selecting outside stud dogs, require genetic test documentation. If your bitch is a carrier, use only clear studs. If your bitch is affected, use only clear studs and consider this mating more carefully, ensuring other health traits justify the combination.

Puppy Placement

Test all puppies before sale. Affected puppies can make wonderful pets and should be placed accordingly, with clear disclosure of their status and the information owners need for appropriate care. Consider creating a care guide for affected puppy buyers.

Clear puppies from your programme are valuable; consider co-ownership arrangements that ensure their breeding potential benefits future generations.

Record Keeping

Maintain detailed records of all test results, mating decisions, and offspring status. This data enables analysis of your programme's effectiveness and contributes to breed-wide knowledge when shared appropriately.

Long-Term Perspective

Reducing CEA prevalence is a multi-generational project. Breeders who commit to this work may not see its full fruits in their own breeding careers. What matters is consistent, incremental progress; each generation slightly better than the last.

I find immense satisfaction in tracking lines I first examined decades ago. Seeing descendants with clear status where grandparents were affected validates the patient work of dedicated breeders. These improvements, accumulated across thousands of breeding decisions by hundreds of breeders, reshape breed populations for the better.

The tools available today; accurate genetic testing, comprehensive clinical examination protocols, open health databases; would have seemed miraculous to breeders struggling with CEA fifty years ago. We owe it to our dogs and their future generations to use these tools wisely.

CEA need not remain as prevalent as it currently is in affected breeds. With knowledge, commitment, and cooperation, breeders can dramatically reduce the burden of this condition whilst preserving everything we value in our dogs. The path forward is clear; the journey requires only our willingness to walk it together.

For additional perspective on managing multiple hereditary conditions in herding breeds, coordinated health screening programmes offer frameworks applicable beyond CEA alone.