What is a Double Dilute?

From the February 2014 issue of The Stable Magazine – www.thestablemagazine.com/february 2014

A quick lesson in horse genetics...

‘Double Dilutes’ are horses who possess two cream dilution genes - namely, cremellos and perlinos. What are cremellos and perlinos, you ask? What makes them so special? Are these albino horses? 

‘Double dilute’ is the general term given to horses who carry two copies of the cream dilution gene. Most commonly, we recognise these horses as CREMELLO or PERLINO horses. Double dilutes always have blue eyes and pink skin - but there are subtle differences between the way these horses look - and an even larger genetic difference! The dilution gene acts to ‘wash out’ a horse’s coat colour. A cremello (like the one on this page) actually has a base coat colour of chestnut. He inherited a dilution gene from his sire. This first dilution gene would have changed this horse’s base coat from chestnut to palomino. But wait! He’s a double dilute - so he has also inherited another cream dilution gene from his dam. The second dilution gene washed his coat from what would have been palomino, to cremello.

ARE DOUBLE DILUTES ALBINO HORSES?

No - Double Dilutes are not albino horses. Although up until 2003, you couldn’t register a cremello or perlino foal with the AQHA, as prior to the cream dilution gene being fully understood, these horses were thought of as albino horses. We now know that this is not the case.

WHAT BREEDS ARE DOUBLE DILUTES?

Double dilutes are no specific breed - cremellos and perlinos are just colours that can occur in most breeds of horses when the right genes are crossed. Most commonly, you’ll see cremello and perlino quarter horses, miniature ponies, welsh ponies - and many other breeds. Palomino and Cremello Thoroughbreds are even now cropping up

ARE THEY ANY DIFFERENT TO ANY OTHER COLOURS OF HORSES?

No - not in any genetic way. It has been previously thought that horses with blue eyes (known as ‘wall’ eyes) were blind or vision impaired, but this is another fallacy. The only real negative to owning a cremello or perlino is protecting their pink skin from sunburn - just as you would with horses with large white face markings.

DID YOU KNOW?

If you breed a cremello to a chestnut horse, you will ALWAYS get a palomino? Or that two cremellos will always produce a cremello foal?

Very basically, here we are looking at three base coat colours - Chestnut, Bay and Black. Horses of these colours do not carry any cream dilution gene. The cream dilution gene is called as such because it dilutes the horse’s coat colour - almost like washing it out a shade. One very interesting thing about the cream dilution gene is that it is what is referred to as an incomplete dominant allele. It is not always possible to tell that a horse is carrying this allele just by looking at it - in the case of Smokey Black (sometimes called Black Buckskin) horses - but you are able to tell that some horses definitely carry the gene - such as in the case of Palomino and Buckskin horses, as the gene is always expressed. Just by looking at a palomino horse, you can know that it carries one copy of the cream dilution gene - and that it is what is called a ‘single’ dilute. Buckskin horses are the same, having one cream dilution gene. Smokey Black horses also carry one cream dilution gene, but it can be difficult to confirm that the horse’s colour is in fact Smokey Black without it having at least one single or double dilute parent.

SMOKEY BLACK

Normal ‘true’ black horses carry a ‘black’ base colour gene only - no dilution gene. When a true black is crossed with a palomino, buckskin, or double dilute the foal may have one cream dilution gene - therefore technically making it a ‘Smokey Black’. These Smokey Black horses are dilutes - (single dilutes, though, not doubles!) but they probably look the same as any black or dark brown horse, as the gene is not expressed. Some Smokey Black horses do have a distinctive red sheen to their coats. DNA tests can confirm the presence of a cream dilution gene - or if the horse in question has a double dilute parent, or sires/gives birth to a double dilute foal, it does definitely carry the cream dilution gene.

SMOKEY CREAM

Smokey Cream horses do exist! A horse with a black base coat and two copies of the cream dilution gene makes the horse appear similar in colouring to a cremello or perlino. Like the other double dilutes, Smokey Cream horses also have blue eyes and pink skin - but they are very difficult to distinguish from cremellos and perlinos.

OTHER COLOUR COMBINATIONS:

Other factors that make equine genetics less of a guessing game and more of a probability challenge include things like pinto genes, roaning, overo and tobiano genes - and even pintaloosa genes! Miniature ponies are now bred in heaps of different colours, so much so that now you may find a double dilute pintaloosa - meaning it carries dilute genes, spotted genes AND pinto genes!

Thank you to The Stable Magazine for this article, which was originally published in their February 2014 issue. Check out The Stable Magazine online now for FREE. Read this article and many more at www.thestablemagazine.com