Albinism in Horses

Albinism occurs in a lot of animals; mammals, reptile, birds, it even affects humans. As of yet, though, there have been no reported cases of albinism in horses. Many people think and even speak with confidence about owning or seeing an albino horse – but albinism has never been reported by any stud farm, there are NO true albinos! This article sets out to explore why that may be and exactly what these people are mistaking for albinos.

The definition of albino is:

A person or animal having a congenital absence of pigment in the skin and hair (which are white) and the eyes (typically pink).

Baring this in mind, I will explain why there are no true albino horses.

Basic horse genetics

A good place to start is with the basic colour genetics of horses. Understanding the foundations of coat colour genetics is important for understanding the coat colours people mistake for albinos.

The very basic colour genetics start with base colours; these are the colours black and chestnut. Dilution genes are added to create new colours. The most common dilution gene in horses in the Agouti gene which causes the bay colouring on a horse with a black base colour.

Bay - Caused by the Agouti gene, which restricts the black pigment to the legs, mane and tail.
Brown – Caused by a form of the Agouti gene which restricts the black pigment to soft areas of the body (sometimes called seal brown or tan)

Grey

Most commonly seen “white” horses are usually greys. They differ from real white horses in many ways.

Grey horses are born any ordinary colour (bay, black, chestnut etc.) Gradually over time they will “grey out” which is where more and more grey hairs appear in the coat, some grey horses get to a point where they look almost brilliant white, others will form dapples, or stay a steel grey colour for the majority of its life, and some older horses can form flicks of colour called “flea bitten grey”. The occurrence of “greying out” varies from horse to horse, some horses start to grey out at a young age of around 3 or 4 months old and some will show no signs of grey until several years later.

Grey horses which look brilliant white can be told apart from white horses by their skin colour. Because grey horses are born a darker colour they have darker skin (usually black or dark grey skin), these are noticeable around areas where the coat is thin, such as around the eyes, in the ears and the muzzle. Grey horses usually have brown eyes.

Extreme or Maximum Sabino

Sometimes Sabino horses are mistaken for white or even albino due to their eye colouring.

Sabino horses are a group of horses who have a white spotting pattern on their coats. There are many extremes of Sabino colour, in the heterozygous state there are usually only a few flicks of white. In the Homozygous state they can be almost completely white – and in some cases they are born completely white. Other colourings like Tobiano or Overo may be present in a heterozygous Sabino, which may make them appear mostly white. A horse which is both Tobiano and Sabino is referred to as Tovero. Sabino horses can have blue, partially blue or brown eyes – so it can be easy to mistake them for an albino (it’s important to note that true albinos have red, pink or violet eyes)

(References: http://www.horsetesting.com/sabino1.htm)

Cremello

Cremello horses are often mistaken for albino horses due to their pink coloured skin and blue eyes.

Much like bays, Cremello colouring is caused by a dilution gene – this gene is commonly called the cream dilute. Cremello is a double dilute which is derived from the base colour chestnut. Cremello horses have blue eyes and pink skin, they’re not exactly white (more an off white or cream colour) but can appear white.

Base colour	One cream dilute	Double dilute
Chestnut	Palomino	Cremello
Black	Smokey Black	Smokey Cream
Bay (Agouti dilute)	Buck skin	Perlino

(Double dilute information: http://www.doubledilute.com/color-chart.htm)

White

Finally, we are onto the white horse. The true white horse is caused by its own “white” gene.

In the existence of the dominant white gene (Ww) a horse will be born white. The skin will be pink; the eyes are usually brown (but can sometimes be blue). A true albino cannot produce any pigment therefore making the eyes red or pink. Since the eyes in a white horse are actually brown, therefore not lacking pigment, it would be incorrect to call a white horse albino. They are not truly albino! Horses with ww (non-dominant white) will not be white.

Lethal White

The white gene is truly dangerous in horses – this may offer an explanation as to why there are no albino horses alive today!

There are two types of lethal white: Embryonic Lethal White and Overo Lethal White.

Embryonic Lethal White
Some theories suggest that in the presence of the homozygous dominant white gene (2 dominant white genes, WW), the foetus will be naturally absorbed by the mare in early pregnancy. Since no horse has ever survived past early foetal stages with this gene, we are not sure whether it would be the albino gene or not, although it is likely this is the case. It is not clear what causes this to happen.

Overo Lethal White
In the presence of the homozygous dominant Overo gene, outwardly healthy foals die within the first few days of life. This is due to the defective Overo gene (frame Overo) which is passed on by both parents.


Hopefully this has explained why there are no albino horses, while also explaining why what you may have thought was albino is not!

Christmas of 2009

I just wanted to share my Christmas screen shots with you! These shots are from City folk from 2009 in the month of December, they aren't in order of date.

I spent some of Christmas Eve in a friends town and we had a lot of fun

I caught sight of Jingle! (He's real!)

Me and Jonny made some snowmen

Jonny's snowman was not happy at all with his disproportionate head

A tiny melting snowman :(

Meeting and greeting animal villagers in Waldo, the town I was visiting! 

Ahh, that was a good Christmas!