Grey Horse Genetics: How and Why Horses Turn Grey
By Breedio team
In short
Grey is a dominant gene that slowly removes pigment from the coat. Learn how to spot a future grey foal, what the greying stages look like, why melanoma matters and why the birth coat belongs on the papers.
A grey horse carries one dominant gene that progressively depigments its coat, so a foal born bay, black or chestnut turns lighter year after year until it is nearly white. Because the gene is dominant, a grey foal always has at least one grey parent, and a horse with two copies passes grey to every foal. This guide, part of the coat colour series, covers how to recognise a future grey in 2026, the stages of greying, the melanoma question and why the birth coat matters.
What is the grey gene and how does it work?
Grey is not a colour in itself. It is a modifier that sits on top of whatever base coat the horse was born with (chestnut, bay or black). The base colour is still there genetically: a grey horse is a bay, a black or a chestnut that is gradually losing its pigmentation.
Key points:
- Dominant inheritance. One copy is enough. As the University of Kentucky's Gluck Equine Research Center notes, a grey horse must have at least one grey parent.
- Progressive, not instant. The coat bleaches over the years. The speed varies from one horse to another.
- Skin stays dark. Unlike cream dilutions, a grey horse keeps dark skin and dark eyes.
- Hidden base colour. The underlying Extension and Agouti genotype still determines what the horse would look like without grey, and it is still passed on.
Two grey parents do not guarantee a grey foal, because a heterozygous grey passes the gene to about half of its foals. A non-grey foal from grey parents simply shows the base colour it inherited.
How can you tell a foal will turn grey?
Foals are born coloured, and the birth coat can be misleading. Early signs to look for:
- Grey hairs around the eyes. This is often the first sign, sometimes within weeks of birth, giving a spectacled look.
- Grey hairs on the muzzle, face and legs appearing in the first months.
- A birth coat that looks darker than expected. Many future greys are born a dark bay, brown or black and are mistaken for non-grey foals.
- Parentage. If neither parent is grey, the foal cannot be grey. If one parent is grey, check whether the grey parent is homozygous.
A grey foal can be hard to tell from a dark bay in its first weeks. Photograph the foal at birth, then again at a few months, and compare the eye and muzzle area.
What are the stages of greying?
Greying follows a recognisable sequence, though the pace differs between individuals and between lines.
- Steel grey or iron grey: the first stage, when white hairs mix into the base coat and the horse looks dark grey.
- Dapple grey: lighter rings of hair form on a darker background, typically on the quarters, belly and flanks. Dapples are most obvious while the horse is mid-way through greying and tend to fade as the coat whitens.
- Light grey: the dapples fade and the coat becomes mostly white, often keeping darker hair on the legs and points for a time.
- Flea-bitten grey: small flecks of pigment, often reddish or dark, reappear on an otherwise white coat. Not every grey horse goes through this stage.
- White (fully grey): an almost white coat with dark skin showing at the muzzle, eyes and under the dock.
The skin stays dark throughout, which is how a grey horse is told apart from a true white or a cream dilute.
What does the greying timeline look like?
The table below summarises the general pattern. Timelines vary a lot between horses, so treat the second column as a guide, not a schedule.
| Birth coat | Typical greying timeline | Birth colour to record on the papers |
|---|---|---|
| Bay | Grey hairs round the eyes and muzzle first, then iron grey, dapples, light grey over the years | Bay |
| Black | Grey hairs round the eyes first, then dark steel grey, dapples, light grey | Black |
| Chestnut | Whitening is often noticed as a lightening of the mane, tail and body, with a flea-bitten phase common in older horses | Chestnut |
| Dark bay or brown that looks non-grey | Subtle early signs only, which makes the foal easy to misjudge at birth | Dark bay or brown, as observed at birth |
Why do the papers record the birth coat of a grey horse?
In France the coat on the papers is recorded by the SIRE/IFCE. For a grey horse, the visible colour is a moving target: the same horse may look dark grey at 3 years old and almost white at 12. The birth coat is the only stable piece of information about what the horse was genetically underneath.
That is why entering the birth colour matters:
- Coat predictions. To estimate what a grey horse's foals could be, a calculator needs the base coat (chestnut, bay or black) and not just the word grey.
- Hidden genes. A grey horse can carry cream, dun, tobiano or other genes under its white coat, and the birth coat and the grandparents help to reveal them.
- Traceability. Identification documents stay useful for the life of the horse even when it looks nothing like its foal photo.
If you own or breed grey horses, photograph each foal at birth and note the exact coat before the greying starts. Ask your breeder or the stud book for the birth coat if you buy an older horse.
What about homozygous greys?
A horse has two copies of the gene when it inherited grey from both parents. The rules are simple:
- Homozygous grey (two copies): passes grey to 100% of its foals, whatever the mate.
- Heterozygous grey (one copy): passes grey to about 50% of its foals when bred to a non-grey horse.
- Non-grey: cannot pass grey.
The grey DNA test detects the mutation and, at most labs, reports one or two copies. The breeding record is a useful cross-check: a horse that has produced only grey foals out of non-grey mates, over several foals, is very likely homozygous. A single non-grey foal proves it is heterozygous.
This matters for planning. If you want a grey foal, a homozygous grey stallion removes the uncertainty. If you want to avoid grey, a grey parent is a risk you cannot manage by mate selection alone.
Is there a link between grey and melanoma?
Yes, and it is well documented in the veterinary literature. Grey horses are more prone to melanocytic tumours than other coat colours, and the risk rises with age. Most grey horses will develop at least one melanocytic lesion as they get older, although the number, location and behaviour of the lesions vary widely.
What breeders and owners should know:
- Typical sites: under the tail and around the anus, the perineum, the sheath and udder area, the lips and the base of the ears.
- Many are slow growing. Some stay small and stable for years, while others grow, ulcerate or spread.
- Examine regularly. Look under the dock and around the genital area during routine checks, and photograph any lump to monitor changes.
- Call the vet for any nodule that grows quickly, ulcerates or sits where tack or foaling may irritate it.
This is a reason to think about grey before breeding, not a reason to avoid it. Grey horses can live long, healthy and productive lives, and many breeders keep high-quality grey lines. A vet exam, including the perineal area, is a sensible part of the check-up for an older grey broodmare or stallion.
How does grey interact with other coat genes?
Grey masks the others as it progresses, which is why testing and family records are so useful. A grey horse can still be:
- Bay, black or chestnut underneath, depending on Extension and Agouti.
- A cream carrier, producing buckskin, palomino or cream foals when bred to the right mate.
- Tobiano or roan, both of which can be hidden by the whitening coat.
- Dun, with primitive marks that disappear under the greying coat.
A coat does not show every gene. A calculator gives a range of possible foal colours; grandparents' coats narrow it down, and a DNA test confirms the genotype.
How can you predict the coat of a foal from a grey parent?
Use the foal coat colour calculator. Enter the coat of the mare and the stallion, and for each grey parent add its birth coat, its parents' coats and any DNA result you have. The tool covers the Grey gene alongside Extension, Agouti, Cream, Champagne, Silver, Dun, Roan, Tobiano and Frame overo, and gives the foal's possible adult coats with their odds. It also warns about lethal white (OLWS) risk when frame overo is involved.
The more information you enter about the grey parent's birth coat and family, the narrower the prediction. Browse the other Breedio tools for the rest of your breeding season.
Key takeaways
- Grey is dominant: a grey foal needs a grey parent.
- Foals are born coloured, often darker than expected, with grey hairs around the eyes first.
- Dapple grey and flea-bitten are stages, not separate genes.
- A homozygous grey always passes grey; DNA tests usually report one or two copies.
- Grey horses are prone to melanocytic tumours with age, so regular checks matter.
- Record the birth coat: it is the only stable proof of the base colour.
To see what your next foal could look like, run the mating through the foal coat colour calculator.
