Equine Genetic Disorders and DNA Profiling

Some registered horse breeds require genetic disorder testing for sire-registered stallions, and record positive results on registrations. In this article, we're exploring the requirements of the Australian Stock Horse Society (ASHS) for registered Australian Stock Horses.

Common tests offered in Australia include: OLWS (frame/overo lethal white), HYPP, HERDA, PSSM1, Malignant Hyperthermia (MH), and GBED. These are standard in a 6-panel used by ASHS.

DNA profiling (genotyping) is used for identification and parentage verification; several Australian labs and services provide profiling and parentage/registration testing.

Disorders commonly included in ASHS’s 6-panel GDT

• OLWS / Frame Overo (Lethal White Overo) - a coat-pattern mutation that in homozygous foals causes a non-viable intestine problem; typically tested as a recessive/carrier check.
• HYPP (Hyperkalemic Periodic Paralysis) - muscle weakness/episodes; caused by a dominant SCN4A variant (one copy can produce disease). Important to avoid breeding affected animals.
• HERDA (Hereditary Equine Regional Dermal Asthenia) - severe skin fragility (like Ehlers-Danlos in people); autosomal recessive in Quarter-horse related lines.
• PSSM1 (Polysaccharide Storage Myopathy type 1) - a glycogen storage disorder causing muscle stiffness/exertional rhabdomyolysis; caused by a GYS1 mutation (dominant risk; management important).
• MH (Malignant Hyperthermia / RYR1 variants) - exercise/anaesthesia-related muscle crisis risk (often tested alongside PSSM because interactions can worsen symptoms).
• GBED (Glycogen Branching Enzyme Deficiency) - lethal recessive disease in foals (related breeds); carriers are common in some bloodlines.

DNA profiling & parentage testing — what it is and why do it

• DNA profile / genotyping: lab determines a set of genetic markers unique to the horse (used for identification, theft recovery, and registration). Parentage testing compares profiles to verify sire/dam.
• Many breed registries (including Australian bodies) require profiles or will accept accredited-lab reports for registration and parentage confirmation. Check the registry’s preferred lab list or procedures before ordering.

How to get tested in Australia (labs, sample types, costs)

• Labs/services in Australia: Practical Horse Genetics (orders/tests online), Racing Australia / Equine Genetics Research Centre (EGRC) in Scone (services for breed associations), plus other private providers. Choose an accredited lab if you need results for registration.
• Sample types: preferred - mane/tail hair with roots (20–40 hairs) OR cheek (buccal) swabs (some labs prefer swabs). Follow the lab’s sampling instructions exactly (paper envelope, avoid plastic bags that can cause mold, clearly label).
• Costs (examples / ballpark): ASHS lists the 6-panel GDT (for horses already DNA-profiled with ASHS) at AUD $130 (Jan 2024 GDT price on their doc). DNA profiling/parentage at consumer labs may range (example: a basic 23-loci profile ~AUD $80–$130; see providers for current pricing). Prices vary by lab and whether you need parentage, full health panels or coat-colour panels.

Practical steps / checklist (for breeders, sellers, buyers)

1. Check ASHS / registry requirements: confirm which tests are compulsory for sire registration or sale disclosure and which labs they accept. ASHS specifically requires GDT for sire-registered stallions.
2. Decide which tests you need: at minimum: DNA profile (for ID/parentage) + the ASHS 6-panel if you’re an ASH breeder/seller. Add extra panels (colour genes, other health markers) as wanted.
3. Order the kit from an accredited/recognised lab (Practical Horse Genetics, EGRC via your breed association, or another accredited lab). Follow their sample instructions exactly.
4. Record and disclose results: note positive/carrier results on sale listings and registrations as required. Keep digital copies of lab reports for buyers/registry.
5. If you’re buying: ask the seller for the horse’s DNA profile and genetic-disorder report; ask the registry to confirm records if uncertain.

Interpreting results

• Carrier (heterozygote): usually healthy but can pass the mutation to ~50% of offspring (for recessive disorders). Breed carefully.
• Affected: clinical disease or high risk - management or breeding restrictions apply (varies by disorder).
• Normal/clear: no copies of the tested variant found.

Labs always include a result interpretation page - read it, and consult your vet or an equine geneticist if you see a positive/affected result.