Tracing the grey horse gene

Alcock Arabian - ancestor of all grey thoroughbreds Desert Orchid, Milton, Murphy Himself - all outstanding greys who captured the public's imagination in different equestrian spheres. Grey racehorses, whether due to their comparative rarity or some other quality, tend to attract a disproportionate amount of betting. But greys were not always so popular, particularly with the early thoroughbred breeders when greys were much more common in the breed than they are today. Indeed in the early 20th century it was predicted that in a short time there would be no grey thoroughbreds at all.

A single ancestor

It was The Tetrach, possibly the fastest racehorse ever, who revived the popularity of greys. Most modern grey racehorses trace back to him. Even more surprisingly, all grey racehorses can be traced to a single stallion born in 1704 - the Alcock Arabian (pictured above).

How is it possible to trace the origin of the grey colour to a single ancestor? A horse receives a grey or non-grey gene from each of its parents. If either gene is grey, the horse will be grey. Only a grey horse can pass on the grey gene but a grey could pass on a non-grey gene. This means that a grey horse must have at least one grey parent but grey parents will not necessarily produce a grey offspring. Breeding grey to grey increases the likelihood of a grey offspring and in breeds like the Lippizaner (made famous by the White Stallions of Vienna) this has resulted in a predominantly grey breed.

On the other hand, as the colour cannot skip a generation the colour will only re-appear if another grey is introduced. The apparent exceptions to this can normally be explained by one of the following:

  • incorrect parentage recorded (e.g. the mare was covered by two stallions)
  • horse not recognised as a grey at birth and registered as another colour
  • occurence of a rare white horse (genetically different to a grey as explained below)

The grey colour

Light bay foal with goggles and light muzzle. How can a grey foal not be recognised as such? Greys are normally born dark (not necessarily black as some people believe) and become lighter with age. The colours dapple grey, flea-bitten grey, rose grey, etc. are not separate colours but transitional colours before the horse turns completely white. To add to the confusion grey thoroughbreds which are born chestnut are registered as roan whereas other breeds are often more correctly registered as grey born bay, etc..

Same horse as a yearling. The face of a grey lightens first and it is common for a foal which will turn grey to have white hairs around the eyes (known as goggles) and muzzle as shown above. The same horse is pictured to the left as a yearling and shows the face marking which was only visible after loss of foal coat. Usually the darker the foal at birth the longer it takes to turn completely white. The process typically takes 5-10 years although it can happen much quicker.

One of the reasons for greys being unpopular in the past (apart from the extra work needed to keep them clean!) was that it was believed to be a sign of premature aging. Indeed the process is similar to a person's hair turning grey but it happens much more quickly in grey horses. The grey horse does not actually age more quickly than other colours. The only possibly harmful effect of the greying process is that the pigment is redeposited in the gut and skin and can result in growths known as melanomas. Although these growths are not malignant they can cause problems depending on where they occur.

Colour patterns

During the greying process greys may show different patterns of coloured hair (giving rise to the colours mentioned above). A flea-bitten grey retains flecks of coloured hair over the entire body (and in some cases never turns completely white). Sometimes the flecks become concentrated on a part of the body, usually the shoulders or buttocks, which because it gives the impression of dripping blood are called blood markings. One 18th century stallion was called Bloody Buttocks because he had such markings on his hip. The showjumper Carlow Cruiser (who recently came 3rd in the Hickstead Derby has markings on his shoulder.

The Tetrarch aka The Spotted Wonder Another type of pattern which can occur are large spots known as Tetrach spots after the famous racehorse which had them. The Tetrach, despite only racing as a two-year-old, was a great favourite with the public and his spots together with his brilliant performances resulted in the nickname The Spotted Wonder.

Mumtaz Mahal aka The Flying Filly The Tetrach's daughter Mumtaz Mahal inherited the spotting along with his amazing speed - earning her the name The Flying Filly. (SHe is pictured later in life when her colour had become dappled grey.) The spotting is not directly connected to the grey colour although it is usually not obvious on darker colours. This means that the spotting characteristic can be passed on through non-greys and re-appear when another grey is bred into the line. It often appears in the Norther Dancer line which traces to The Tetrach through Mahamoud.

White horses

Horses are occasionally born pure white. Unlike greys these have pink rather than dark skin and are born to dark parents. The colour seems to result from a rare combination of different genes and is not related to the grey gene.

More information

Posted on 13 July, 2011

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