Overo Pinto: A general identification guide
by Samantha Kroese
I’m not going to go into the strict genetics of all the patterns and how they relate because I mostly wanted to write this as a more general article for identification purposes. I am certainly NOT a genetics expert and it pays to keep in mind that every day the information is changing and we are learning more about colors. While there is a lot of great information available online always keep in mind it could be outdated and incorrect (even this article!) so make sure to do your own research too.
Overo is a pinto term that at one time was the defining term for pintos. There were Tobianos and then everything else that was pinto was Overo.
Tobiano was once termed as any pattern that crosses the back (a lot of people think that means between the withers and dock but it actually encompasses the entire spine from the skull base to the very end of the dock) but some forms of Sabino and Splash can also cross the back.
As genetics move forward and there are more and more tests available we are learning that there are many different genes that control Overo patterns and they’ve been given names.
Frame Overo is one of the most common overo patterns so let’s discuss that one first. A frame overo horse can be any of the base colors (Black, Bay, Brown, Chestnut and their modifiers and dilutions). Their markings often appeared ‘framed in’ by color. The markings are usually jagged instead of round. Sometimes white crosses the back but it is rare on a frame. The legs are usually dark but the head is more often than not white or bald.
Frames are controversial because a homozygous frame foal will be born with a disease known as lethal white and it will die within 72 hours. Thankfully there is now a test for real horses and if you avoid breeding two frame overos together (or any carrier of this gene it has been found that even horses without the frame overo expression can carry this dangerous gene if they have frame in their background) then lethal white isn’t even a worry.
Places to read more about Frame Overo:
There are some great examples of Frames on this page: http://www.manyponies.com/articles/paintphotogallery.htm
Splash Overo (aka Splashed White):
Splash is the less common pattern of Overo. Horses with splash will look like someone dipped them in paint. The color rises from the bottom of the horse like a paint ‘splash’. The bottom of the horse and their legs are usually white with a splash. The edges of the markings are usually crisp instead of jagged and have a ‘sharp’ appearance. Splash can hide as minimal. Splash is also thought to cause blue eyes. Splash white is bold normally with large unbroken white swatches. Heterozygous Splash can be minimal, it can express as just a blaze or even just a snip.
A lot of great examples of Splash and more information on the pattern on this page: http://www.mustangs4us.com/Horse%20Colors/splashed_white.htm
There is also a lot of good documented information here: http://en.wikipedia.org/wiki/Splashed_white
Sabino is the odd one out. It is ‘overo’ because it is not Tobiano but aside from that it doesn’t really fit in with the other overo patterns. Genetically it’s quite different. There’s still a lot to learn about Sabino and how it expresses and what genes cause it.
Sabino can occur in many breeds even ones with no other form of pinto. There is thought that perhaps a form of Sabino is responsible for all face/leg markings in horses. There have been just a few Sabino genes identified so far but there are horses that display Sabino without those genes so there is thought there are more that aren’t discovered yet.
Sabino can express in very minimal forms, a blaze or a sock, or a snip that goes over the lips/chin. A white chin usually indicates Sabino as do socks of any size that point up to the horse’s belly from the insides of the legs. Belly spots are very common for sabino even when there’s no other white on the body of the horse.
Sabino can also express so boldy that the entire horse turns white (known as Maximum Sabino, though there is usually a tiny spot of color somewhere). White horses may also be caused by Dominate White, which is different than Sabino White. (Neither are Albino, as far as anyone knows Albino doesn’t exist in horses!)
Sabino causes lacey edges on markings and it can cause extensive roaning as well. Sabino roans can even mimic true roan sometimes in breeds where there are no true roans present.
The most common minimal sabino expression is four white stockings and a wide blaze that goes down to a white chin. Since Sabino can so commonly hide as normal markings sometimes it’s a shock when a fully expressed one pops out of two rather common looking parents.
Sabino markings usually don’t look as crisp and sharp as the other overo patterns, it looks more like lacey or roany patches. It can cross the back.
Sabino can also cause blue eyes but not exclusively.
Some great examples of Sabinos can be found on this page:
Overo can ‘crop out’ of parents that have minimal markings. This happened a lot in the Quarter Horse breed but can happen in others.
Most Clydesdales have a form of Sabino (though not the currently identified gene).
Overo can even express in breeds you might not be aware of!
There are even purebred Thoroughbreds with Splash, Frame, and Sabino http://www.whitehorseproductions.com/tbcolor3.html
Sabino is rather well known to occur in the Arabian horse breed (though it’s not caused by the currently identified Sabino gene). The other forms of Overo have not been proven to exist in the breed though.
Frame Overo has been found in Morgans (though they are not currently allowed to show at Morgan shows):
I hope this helps people at a quick glance to know what patterns their Overo might have. Remember you can have a combination of these patterns (and even Overo and Tobiano to make things more confusing) but this should give you an idea what you may be dealing with on oddly marked horses.
*Please note: As stated above this is not law and is subject to change daily when new genetic break-throughs happen. I am not a geneticist all my information is gleaned from various other sources and while I researched as much as I could to see that it was correct there may be flaws. This is only meant to be a general identifier article not one with genetic certainties. Always do your own research of many sources to back up any claims you find online about anything to do with horse color!