Colour Genetics 4: Grey Horses
This is post number 4 in this series! If you need a refresher in basic genetic lingo and inheritance, check out post #1!
Grey (G) is a kind of dilution gene, but unlike Pearl or Cremello for example, (see Colour Genetics 3) horses carrying the grey dilution gene will not affect their base coat until they gradually lose their pigmentation as they age. Some foals will show signs that they will grey out, however, not all will. Often, if they indicate as a foal that they will grey out, the foal will appear to be wearing "grey goggles": a term used to describe grey rings around their eyes. These goggles are most apparent on bay foals.
Grey is a dominant gene, meaning that if a horse carries even one copy of the gene they will grey out as they age. Heterozygous Greys (G/g) have a 50% chance of having grey foals, and homozygous Greys (G/G) will always have grey foals. Some horses, especially G/g, may exhibit a pattern known as "flea-bitten" grey.
Flea-bitten grey's will end up almost as white as other greying horses but instead of becoming almost 100% "white", they will be covered in little flecks of colour that look like flea bites. These "bites" usually are the base colour of the horse, a.k.a. the colour of the horse before it began to grey out / its base coat colour.
As this process lightens the horses coat for their entire life, different stages of grey have been given different names. They will all end up looking "white", but their black skin confirms that they are a grey horse and not "white". "White" horses do not actually exist, but this will be discussed in Colour Genetics 5! (Pink skin will continue to underlay any white markings the horse has).
More markings associated with grey horses will be posted with the more comprehensive photo collection of grey horses.
Grey horses are commonly affected by melanomas, a kind of skin cancer that affects the pigment producing cells called melanocytes. They so commonly have melanomas that I felt it worth mentioning here. Apparently, while there is always a risk that some benign tumour can become malignant, grey horses seem to fight off melanoma better than other mammals. But of course, these lumps should always be checked out by your veterinarian!
Some breeds are more associated with grey than others, like Lipizzaners, who are almost always grey, and this gene is also unusually common in Arabians and Thoroughbreds (and a few draft breeds) compared to other breeds.
Here are some photos of the greying-out process!
A grey mare with her bay foal. You can't see any grey goggles in this image, but because the dam is grey, this foal will very likely be grey when he is older, regardless of the studs coloration (remember, G is dominant! So even if the mare is G/g, then there is a 50/50 chance of this foal being grey!)
An early stage of grey, but this horse could also be a blue roan. Roan is caused by a different gene, but young horses greying often become confused for a roan.
A beautiful dappled grey horse. Dappling is caused by the silver gene and can affect non-grey horses as well. You can tell that this horse was bay as a foal.
A beautiful example of two grey horses. The one on the left is significantly lighter in colour than the one on the right, who is a flea-bitten grey.
Grey (G) is a kind of dilution gene, but unlike Pearl or Cremello for example, (see Colour Genetics 3) horses carrying the grey dilution gene will not affect their base coat until they gradually lose their pigmentation as they age. Some foals will show signs that they will grey out, however, not all will. Often, if they indicate as a foal that they will grey out, the foal will appear to be wearing "grey goggles": a term used to describe grey rings around their eyes. These goggles are most apparent on bay foals.
Grey is a dominant gene, meaning that if a horse carries even one copy of the gene they will grey out as they age. Heterozygous Greys (G/g) have a 50% chance of having grey foals, and homozygous Greys (G/G) will always have grey foals. Some horses, especially G/g, may exhibit a pattern known as "flea-bitten" grey.
Flea-bitten grey's will end up almost as white as other greying horses but instead of becoming almost 100% "white", they will be covered in little flecks of colour that look like flea bites. These "bites" usually are the base colour of the horse, a.k.a. the colour of the horse before it began to grey out / its base coat colour.
As this process lightens the horses coat for their entire life, different stages of grey have been given different names. They will all end up looking "white", but their black skin confirms that they are a grey horse and not "white". "White" horses do not actually exist, but this will be discussed in Colour Genetics 5! (Pink skin will continue to underlay any white markings the horse has).
More markings associated with grey horses will be posted with the more comprehensive photo collection of grey horses.
Grey horses are commonly affected by melanomas, a kind of skin cancer that affects the pigment producing cells called melanocytes. They so commonly have melanomas that I felt it worth mentioning here. Apparently, while there is always a risk that some benign tumour can become malignant, grey horses seem to fight off melanoma better than other mammals. But of course, these lumps should always be checked out by your veterinarian!
Some breeds are more associated with grey than others, like Lipizzaners, who are almost always grey, and this gene is also unusually common in Arabians and Thoroughbreds (and a few draft breeds) compared to other breeds.
Here are some photos of the greying-out process!
 |
| https://pixabay.com/photos/the-horse-mare-offspring-horses-2388276/ |
A grey mare with her bay foal. You can't see any grey goggles in this image, but because the dam is grey, this foal will very likely be grey when he is older, regardless of the studs coloration (remember, G is dominant! So even if the mare is G/g, then there is a 50/50 chance of this foal being grey!)
 |
| https://pixabay.com/photos/horse-equine-horse-color-gray-dapple-4275210/ |
An early stage of grey, but this horse could also be a blue roan. Roan is caused by a different gene, but young horses greying often become confused for a roan.
 |
| https://pixabay.com/photos/horse-running-korda-lynx-stallion-4409714/ |
A beautiful dappled grey horse. Dappling is caused by the silver gene and can affect non-grey horses as well. You can tell that this horse was bay as a foal.
 |
| https://pixabay.com/photos/arabians-horses-equines-animals-2395184/ |
A beautiful example of two grey horses. The one on the left is significantly lighter in colour than the one on the right, who is a flea-bitten grey.
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