Dog DNA Tests: What They Get Right

Dog DNA testing works considerably better than the cat equivalent, because centuries of hard selection produced breeds that are genuinely distinct populations. There is real signal to read.

That does not mean every number in the result means something.

What is reliable

Major ancestry. If a test says half German Shepherd, that is likely to be broadly right. The larger the fraction, the more confidence it carries.

Health markers. These are direct tests for specific mutations rather than statistical inference, and they are as reliable as the assay.

Physical trait genes — coat length, shedding, colour, size. Simple genetics, read cleanly.

What is not

Small percentages. Anything under about ten per cent is close to noise. A result listing seven breeds at five per cent each is describing uncertainty, not seven great-great-grandparents.

Agreement between companies. Different reference panels produce different answers on the same dog, sometimes strikingly different. If two tests disagree, neither is lying; the method is approximate.

Underrepresented populations. Village dogs, landrace types and regional street dogs are thinly covered in reference panels and get assigned to whatever breed they most resemble.

Behaviour. No test predicts it. The large 2022 study combining owner surveys with genome sequencing found breed explained around nine per cent of behavioural variation between individual dogs.

The health panel is the point

This is where a test earns its cost, and one result stands out.

MDR1. Dogs with this mutation cannot clear certain drugs from the brain, and normal doses of ivermectin, loperamide, some anaesthetics and several chemotherapy agents cause severe neurological reactions. It is common in herding breeds and in herding-type mixes — which are extremely common dogs. The test is cheap, the result is actionable, and it goes on the file at your vet.

Others worth having:

• Degenerative myelopathy — common in German Shepherds, Corgis and others
• Exercise-induced collapse — Labradors and retrievers
• Progressive retinal atrophy — many breeds
• Von Willebrand disease — a bleeding disorder that matters before surgery
• Hyperuricosuria — affects diet management

A carrier result is not a diagnosis; it is information for a vet.

Reading a breed result honestly

A mixed dog reported as 40% Labrador, 25% German Shepherd and 35% "supermutt" is a mixed dog with some Labrador and some Shepherd. The remainder is the panel saying it cannot resolve further.

If you are hoping to confirm a shelter's guess, be prepared for it to be wrong — that is the normal outcome, and it is the point made in why visual breed identification mostly does not work.

What it will not do for you legally

Breed-specific legislation is generally enforced on appearance, not ancestry. A DNA result showing no bull-terrier ancestry may not change how a dog is assessed under a law written about physical type.

That is a genuine gap and it is worth knowing before spending money expecting a legal defence — the detail is in pit bull is not a breed.

Practical notes

• Swab before feeding, and scrape properly rather than dabbing.
• Choose a test that publishes the specific mutations it screens for.
• Take the health results to a vet. Put MDR1 on the clinical record.
• Treat the pie chart as a conversation piece.

Relatives, and what that feature is for

Most of the large testing companies now show genetic relatives — other tested dogs sharing significant DNA.

For a shelter dog it can identify littermates and occasionally a parent, which is how some owners find out what the actual cross was rather than what the panel inferred. It is the one part of the breed side of these tests that produces hard information rather than an estimate.

It also, incidentally, maps puppy mills: a cluster of closely related dogs sold through different outlets in the same period is a recognisable pattern.