Herding Dog Genetics: Tests, Colors, Selection

Herding breeds are screened for a known list of hereditary conditions: the MDR1 mutation, collie eye anomaly, progressive retinal atrophy, HSF4 cataract, SOD1 degenerative myelopathy, von Willebrand disease, hip dysplasia, autoimmune thyroiditis, exercise induced collapse and vitamin B12 malabsorption. Coat colour in Border Collies and Australian Shepherds comes down to a small set of genes, chiefly merle, FGF5 for coat length and RSPO2 for furnishings. Breeders steer selection with DNA tests, whole genome sequencing, inbreeding coefficients, genetic diversity measures, bottleneck history, estimated breeding values and polygenic scores.

If you keep a herding dog, or you are thinking about a litter, the useful move is to separate three questions that often get mixed together: what can be tested, what a test result actually tells you, and what you do with that number afterwards. The short version is that a DNA test answers one narrow question well, and everything else is a judgement call about the dog in front of you.

Which hereditary diseases are screened in herding breeds?

The list is longer than most owners expect, and it splits into conditions with a direct DNA test and conditions that are scored or measured rather than read off a single gene.

Direct DNA tests exist for the MDR1 mutation, collie eye anomaly, progressive retinal atrophy, the HSF4 cataract, SOD1 degenerative myelopathy, von Willebrand disease and exercise induced collapse. These are the ones where a cheek swab or blood sample gives a genotype: clear, carrier or affected. That result is stable for the dog's life and does not change with age or diet.

Other conditions on the list are not a single gene. Hip dysplasia is scored from radiographs, usually under a scheme that grades each hip. Autoimmune thyroiditis is followed through thyroid panels over time, because a single reading in a young dog can be misleading. Vitamin B12 malabsorption is confirmed by measuring blood cobalamin, often alongside a genetic marker in some lines. Collie eye anomaly sits in between: there is a DNA marker, but a veterinary eye exam still matters, because the condition varies in how it presents.

For anyone working through this list breed by breed, the disease pages at herding breed genetics set out each condition in the same order, which makes it easier to compare what applies to a Border Collie against what applies to an Australian Shepherd or a Collie.

The practical check is simple. Ask which tests were run, ask for the actual report rather than a summary, and check the date. A test run five years ago on different technology may not cover the same variants as a current panel.

How does coat colour genetics work in Border Collies and Australian Shepherds?

Coat colour looks complicated because several genes stack on top of each other, and each one can mask the next.

Start with merle. Merle produces the mottled, patchy pattern familiar in Australian Shepherds. It is inherited in a dominant way, which is why a single merle parent can produce merle puppies. The reason breeders are careful here is that two merle parents can produce double merle puppies, and those dogs are at higher risk of deafness and eye defects. A merle test tells you whether a dog carries one copy, two copies or none, and that is the number that decides whether a pairing is sensible.

Coat length is mostly about FGF5. The long, feathered coat in Border Collies and the fuller coat in many Australian Shepherds trace back to variants at this gene. It is a straightforward trait in inheritance terms, and it is often included on the same panel as the colour tests.

Furnishings, the moustache, eyebrows and leg feathering, are linked to RSPO2. This is the gene that gives some dogs the scruffy, bearded look and others a clean face. It behaves in a fairly predictable way, but it interacts with coat length, so a dog can carry the furnishings variant and still look smooth if other genes pull the other way.

Beyond those three, there is a wider set of colour genes that decide black versus red, whether the dog is solid or spotted, and how much white appears. None of this is a health matter on its own. It matters because colour genetics is often the reason a breeder runs a panel in the first place, and the health results come along with it.

Which DNA tests and breeding tools guide selection in herding dogs?

The tools fall into two groups: tests on the individual dog, and measures of the population the dog belongs to.

On the individual side, a DNA panel covers the single gene conditions listed above, plus colour and coat traits. Whole genome sequencing goes further and reads the dog's full genetic code, which is useful when a breeder wants to look at variants that are not on a standard panel. The catch is that a sequence produces far more information than most people can act on, and much of it is of uncertain significance.

On the population side, the inbreeding coefficient estimates how closely related a dog's parents are, and by extension how much genetic diversity the dog carries. Genetic diversity across a breed is tracked over time, and bottlenecks, the moments when a breed's population dropped sharply, leave a mark that shows up decades later. Estimated breeding values take a measurable trait and estimate how much a dog is likely to pass on, which is more useful than the dog's own score alone. Polygenic scores add up many small genetic effects into one number for a complex trait.

The everyday check for a buyer is to ask what the breeder does with these numbers. A good answer names a specific pairing decision and explains why. A weak answer lists tests without saying what changed as a result.

What does a test result actually tell you?

A clear result means the dog is unlikely to develop that specific condition. It does not mean the dog is healthy in general, and it does not cover conditions with no known genetic marker.

A carrier result means the dog has one copy of a variant and usually will not develop the condition, but can pass it on. Carriers are common in breeds where a variant has been around a long time, and removing every carrier from breeding would shrink the gene pool in a way that causes other problems.

An affected result means the dog has two copies, or in dominant conditions one copy, and is at risk. What that means in practice depends on the condition. Some are manageable with veterinary care. Others are not.

The point of testing is not to produce a pass or fail label. It is to give a breeder enough information to make a pairing that lowers risk without narrowing the breed's genetic base any further.

How do you use this without overreacting to one number?

Treat each result as one input among several. Hip scores, eye exams, thyroid panels and a dog's actual working life all carry weight.

If you are buying a puppy, ask for the parents' test results and the date they were run. Ask whether the pairing was chosen with those results in mind. If you are breeding, look at the breed's diversity picture as well as the individual dog, because a line can be clear on every test and still be too narrow to sustain.

And keep the vet in the loop. A DNA result is a piece of information, not a diagnosis. The dog in front of you is still the thing you are caring for.

The screening overview at the American Kennel Club health desk matches the picture above, and the same habit of recording what changes from week to week is set out in the observation journal guide. Where a drug is involved as well as a gene, the MDR1 sensitivity notes complete the pair.