Sunday, January 29, 2017

The Frame Overo

When I first sat down to go through my photographs, I was hoping to have five or six good examples of the Frame Overo trait. I was pleasantly surprised to find so many mustangs with this particular pattern. Interestingly, I found Frame Overo mustangs only at Sand Wash Basin and Black Hills Wild Horse Sanctuary. It is entirely possible there are some Frame Overos at other management areas, but neither Karen nor I had photographed any of them. The Frame Overo is also unique to North America. This paint pattern is common only in Spanish Colonial Horses or their descendants. However, the trait occasionally but rarely appears in European-derived horses such as Thoroughbreds, Ethiopian breeds, and miniature horses (Sponenberg, 2009).

The Frame Overo Paints are horses that have white patches superimposed on a background of any base colour such as roan, bay, palomino and so on. The white colour often begins as a patch on the neck or barrel and spreads horizontally. The back almost always remains solid coloured between the withers and tail. The white patches are irregularly edged and splashy (Bailey & Brooks, 2013) although some white markings are clean and crisp, similar to tobianos (Sponenberg, 2009). The markings usually do not have the lacy or frosted appearance of Sabino Paints (Kerson, 2015)

The tail is usually one colour and at least one leg is usually solid coloured although often all four legs are solid. If the legs are solid, they may have socks or stockings one might find on a non-paint horse. The markings on the head are often extensive, bonnet or apron-faces are common. Additionally, they may have a pigmented upper or lower lip, or 'moustache' (Sponenberg, 2009).

The genetics are simple, the Frame trait is autosomal dominant, which means a Frame foal must have one Frame parent. However, if both parents have the Frame gene, there is a 25% possibility the foal will be homozygous and have two Frame genes. This foal will not survive because a homozygous Frame is linked to another genetic defect which causes loss of peristalsis (the wave-like action that moves food through the intestines), or more rarely, an incomplete colon. (Bailey & Brooks,2013). More information and examples are located at the bottom of this page.
FF= Normal color
Ff-= Frame Overo
ff= Overo Lethal White

Perhaps one of the best-known Frame Overos is Picasso from the Sand Wash Basin. This handsome Bay horse is one of the most photographed mustangs and he has a Breyer Horse modelled after him. He is a Bay Frame Overo (and possibly carries other paint traits). Many of his numerous offspring are Frame Overos including two know Lethal White foals. There will be more information on this genetic anomaly presented below.


This is an excellent example of a Bay Frame Overo stallion.
Note the white markings on neck and barrel as well as the four solid coloured legs.
Sand Wash Basin, Colorado

The horse on the right is a Chestnut Frame Overo
Sand Wash Basin, Colorado

A small family band with a Sorrel Frame Overo Stallion and a Frame Overo foal. In the management ranges, we cannot be certain of a foal's parentage. Identifying a foal's dam is generally more reliable than the sire. However, mares have been known to steal foals from other mares. Additionally, fillies will leave their natal bands briefly, breed with another stallion, and return to their natal band to deliver and raise the foal within the band they were born. Without genetic testing, we cannot be certain.
Sand Wash Basin, Colorado

A Chestnut Frame Overo. The pigmented lip is common and may appear on the upper lip, lower lip, or both as this mustang mare demonstrates.
Sand Wash Basin, Colorado

The Chestnut Frame Overo is unusual because the right hind leg is extensively marked with white. This may be an anomalous finding, or an indication there are other paint genes present, possibly Sabino. The heavily white face and body markings are more characteristic of Frame Overos.
Sand Wash Basin, Colorado

This charmingly marked dark (liver) Chestnut Frame Overo mare is called 'Crazy Horse'. The freckles on her face are also known as Belton Spots and similar to the spotting found in English Setter dogs. Many horses with Belton Spots on their facial markings, also show "ermine spots" on their legs.  From Sand Wash Basin.

Although not perfectly focused, this Bay Frame Overo has Belton spots on his blaze as well as ermine spots (black spots on socks that are usually found along the coronet band). The ermine spots can cause the hoof to darken and appear striped. From Sand Wash Basin

These two beautiful sparring stallions are from Sand Wash. Kiowa on the left (Bay) and Haze on the right (Sorrel). Haze is a minimally marked Frame Overo- can you find the tiny white mark on Haze?

This is Miss Fleck- she is a Chestnut Frame Overo from Sand Wash Basin: the first image is her as a foal, the second image as a young mare. She was born into Voodoo's band a but later joined Picasso's band (2013). Picasso has since lost his band but he has been doing well as a bachelor. Fleck gave birth to a Lethal White Foal.
Fleck: foal, right side
Fleck: left side

This is Kiowa from the near side (left) from Sand Wash Basin. He had just been in a fight and you can see lacerations on his hip and shoulder. There is also a significant scar on Kiowa's left haunch just below the laceration. It is believed he tangled with either a mountain lion or a wound from fighting that became infected. It is also possible he ran into a fence along the border of Sand Wash Basin and neighbouring ranches.

This is Raindancer. A lovely Chestnut Frame Overo with blue eyes from Sand Wash Basin.

This is an excellent example of a Bay Frame Overo mare from Sand Wash Basin, Colorado with a pigmented lip, flank markings and a small shoulder marking.

Here is a lovely colt Named Van Gogh, he is one of Picasso's many Frame Overo offspring from Sand Wash Basin.

This is Yatzee on the left and a grey stallion on the right from Sand Wash Basin. The grey is actually a Frame Overo - if you look closely at his neck, you'll see the faint outline of the original white mark in the middle, just under his mane. He also has some white markings on his barrel. Some people refer to grey paints as "ghost paints". In the winter it is impossible to tell them apart from solid grey colour horses. A wet grey paint in a summer coat is the easiest to recognise because you can see the underlying skin colour: pink under white markings and darker under the base colour

Another "Ghost Paint- Frame Overo Grey from Sand Wash Basin. The horse on the left has several white Frame markings on his neck, barrel and just above his stifle. He also has the distinctive white apron face with the pigmented lip. The pink skin of the white marking is especially noticeable on this horse's muzzle. If you see a horse with a pigmented lip, there is a good chance they are a paint- often a Frame Overo. The middle horse is also a Frame Overo, this time black with four white stockings.  Four white stockings may indicate this mustang has other paint genes.  The last horse is a Bay Frame Overo with a usual number of white leg markings. Generally, the leg markings do not rise above the knees in Frame Overos.

This family band has two Frame Overos from Sand Wash Basin. The foal, a chestnut beginning to grey-out, and the sorrel stallion. Again, notice the solid coloured legs which help distinguish Frame Overos from Tobiano Paints.

A handsome Grullo Frame Overo gelding from Black Hills Wild Horse Sanctuary Black Hills is a wonderful rescue organisation, please click on the link to find out more

A Black Frame Overo from Black Hill  Wild Horse Sanctuary

Bay Frame Overo with a stunning pattern from Black Hill  Wild Horse Sanctuary. 

Two Black Frame Overos from Black Hill  Wild Horse Sanctuary. Note the tendency for Frame Overos to have solid colour on the spine from the withers to the dock.

Sugar, a Grulla Frame Overo from Sand Wash Basin, Colorado

This stallion is a Chestnut Frame Overo from Sand Wash Basin. It is evident he is thin but these horses receive no care. Many of the horses are underweight from untreated injuries, dental issue, and other injuries or infections that go untreated. It is truly survival of the fittest and only the strongest survive to reproduce. He was a very fiesty stallion, sparring with the bachelors and band stallions.

A dark chestnut Frame Overo Paint from Sand Wash Basin with very little white on his belly (the rest is dried mud)- referred to as a minimal Frame Overo. This stallion is called Spyder. 

A Minimal Dun Frame Overo Paint from Sand Wash Basin.

This beautiful grey colt is a minimally marked Frame Overo. All four legs are solid and there is no white mark on either side. According to Sponenberg (2013), this horse will sire horses with varying amounts of white. Becuase of the lethal white syndrome, any Frame Overo owner should test both horses prior to breeding to avoid the chance of a foal that will not survive. Sand Wash Basin, Colorado

A minimally marked Black Frame Overo from Sand Wash Basin.

A beautiful Black Frame Overo from Sand Wash Basin name Lightning. He was believed to be over 35 years of age at his death one year ago. He is one of the stallions responsible for the Frame Overo trait becoming so prevalent at Sand Wash Basin. He lived all his years free running amongst the Colorado sage.

A minimally marked Bay Frame Overo from Sand Wash Basin with very little white and four solid legs.

Another Minimal Frame Overo Chestnut. This is Mimi, she is a foal by Picasso. Sh has white socks but they are normal height one normally associates with solid coloured horses. The first is her right side, the second image, her left.

A lovely Palomino Frame Overo colt named Meteor. He has a lot of white on both hinds legs (the white goes up the front of the leg to the stifle) and this indicates there is probably another paint gene such as Sabino, is present. Sand Wash Basin, Colorado

Kokomo, a Bay stallion by Picasso and a minimally marked Chestnut Frame Overo mare. Although they are muddy, the mare has solid legs and Kokomo has both white legs marked with white including a thin strip almost reaching his chest. Although he is heavily marked with white, like his sire, they both have solid coloured backs. Sand Wash Basin, Colorado

A very Minimally Marked Frame Overo. The other side is also solid. However, there is a white spot on this stallion's tail evident by the light colour at the end. The facial marking (apron and pigmented lip) are good indicators of a Frame Overo. Sand Wash Basin, Colorado

Lethal White

The Frame Overo (Ff or Oo) trait is found on the equine chromosome #17 at the same locus (location on a chromosome) that controls EDNRB (Endothelin Receptor B) (Sponenberg, 20009). The change in the dinucleotide that occurs in Frame Overos changes an amino acid from isoleucine to lysine which disrupts the function of the EDNRB. In homozygous Frame Overo horses (Ff), the functional inability of Receptor Type B proteins (EDNRB) causes loss of gastric ganglia precursor cell migration and loss of melanocyte migration (Bailey & Brooks, 2013).

The loss of function in EDNRB prevents the embryologic migration of:
  • Gastric ganglia precursor cells from migrating, which means a loss of enervation in the digestive tracts. No nerves ending exist in the colon of these horses and function is completely disrupted. Rarely the loss of EDNRB function results in an incomplete colon (ileocolonic aganglionosis). Foals with either gastric malformation die within a few days of birth and it cannot be surgically corrected.
  • Melanocyte migration means loss of pigment, resulting in white colouration. 

In heterozygous horses, the presence of one "f" results in partial solid colour, but the digestive system is normal. In lethal white, the presence of two "ff" results in a pure white horse (no melanocyte migration) and a non-functional colon, or a blocked, atrophied, or dead-end colon. The loss of gastric enervation has a similar aetiology to Hirschsprung's Disease in humans. Overo Lethal White Syndrome is found in Frame Overo horses as well as highly white calico overo, and frame blend overo (>94%) (Santschi, Vrotsos, Purdy & Mickelson, 2001)

Mingo X Picasso
©Nancy Roberts

©Nancy Roberts

Picasso X Fleck
 ©Danielle M. Williams

 ©Danielle M. Williams

 ©Danielle M. Williams

Here is the link for more information on the Lethal White Syndrome including a handy Punnett Square


Bailey, E., & Brooks, S. (2013). Horse Genetics (2nd ed.). Boston, Massachusetts: CABI.

Gower, J. (2016). Horse Color Explained: A Breeder's Perspective. Brattleboro, Vermont: Echo Point Books & Media, Inc.

Kerson, N. (2015). What Color is that?  A quick guide to horse color identification: Nancy Kerson- Self Published

Santschi, E. M., Vrotsos, P. D., Purdy, A. K., & Mickelson, J. R. (2001). Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. Am J Vet Res, 62(1), 97-103.

Sponenberg, D. (2009). Equine Color Genetics (3rd ed.). Ames, Iowa: Wiley-Blackwell.

***A special thanks to Heather Robson & Nancy Kerson for identification and inspiration, respectively

About the Author & Photographers


Dr. Meredith Hudes-Lowder,
Meredith received a Bachelor of Science Degree from Binghamton University with an emphasis in ethology and genetics. She received a Bachelor of Science in Nursing also from Binghamton and a Masters of Nursing in Perinatal/Women's Health from Stony Brook University. She has a Research Doctorate of Nursing Practice from Stony Brook University. Her doctoral thesis was a research study on cervical cancer screening intervals. She was invited to present her research findings at the podium for the Nurse Practitioners in Women's Health Annual Conference in New Orleans, October 2016. She is a member of several professional organisations and was inducted into Sigma Theta Tau- the Nursing Honor Society in 2007.


Karen McLain: Painter, artist, photographer

Karen McLain is a third generation Arizona native. Growing up in Arizona, she developed a deep appreciation for the outdoors, and for the rural and ranching lifestyle. Karen graduated from Arizona State University with a B.A. in Studio Art. She went on to pursue more traditional and realistic styles, and to create a style of her own. A number of commissioned works are accepted from collectors. The rest of the time, Karen can be found drawing or painting en plein air. These landscapes and life studies of wild horses are then developed into larger works in her studio.

McLain states: ”Painting from life not only reveals natures beauty first hand, but it also challenges me to focus and see clearly the light, form, and wonderful color present.  Time spent in the saddle, and painting en Plein air, results in an outlook that McLain describes as “Drawn from life, and inspired by life”, which is reflected in her work. See Karen’s “studio tour” here


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