Frame/Overo Horses

What is Frame/Overo?

Frame is probably the most well known "Overo" pattern. When North Americans talk about Overo this is the pattern thought of first. Overo is the term used by most to mean "not Tobiano", but since there are three totally different patterns that are called Overo, this generic term is not the best to use when trying to describe the pattern of a horse.

A horse with the Frame pattern will look like it has a "frame" of color surrounding the white. Horses with this pattern will have dark legs. In contrast the head of a Frame horse usually has a white marking that may range in size from a very small star to a large blaze that may be an odd shape. These small markings, such as a star or strip are usually thought to be just a basic white marking but are in fact an indication of Frame, especially if the horse has one or two blue eyes.

White on the body of a Frame horse body will rarely ever cross the topline, but when other white patterns are present it is not uncommon for the white to cross the back so this isn't necessarily a good indicator of the Frame pattern. The spots have clean edges but are usually more jagged than is seen with the Tobiano pattern. The spots on a Frame horse also tend to have more of a horizontal arrangement rather than the vertical arrangement see with the Tobiano pattern.

Another characteristics that occurs with this pattern is for a horse with a white facial marking to have a pigmented upper lip commonly called a mustache. Pigmentation on the lips of a Frame horse usually has a rectangle shape. Blue eyes are very common on Frame horses, even if the eye is surrounded by color rather than white.

Genetic Information
The Frame pattern is a caused by a dominant gene. In the past Frame was thought to be recessive because "Overo" foals have been produced out of parents with no white on the body, these are usually called "crop-outs". Frame has even been called a "dominant-recessive" which makes absolutely no sense. It is much more reasonable and has been proven by further research, that these solid horses are minimally marked individuals that do not have body spots, but do have other characteristics of the Frame pattern and as such they are producing the same as any heterozygous, Frame horse that have white on their bodies. Frame in a minimal expression is very common and occurs in all breeds in which Frame is found. Some Frame horses are so minimal they don't have any white, just blue eyes. You could have horses with the Frame pattern in your herd and not even know it. This is why the Frame/Lethal White test is so important.

The Frame gene in homozygous form is lethal and produces foals that are have OLWS (Overo Lethal White Syndrome). These foals are carried full term, born totally white, although some may have a tiny spot or two of color. These foals have an incomplete lower colon and because of this the foals cannot defecate and die of colic shortly after birth. It is recommended that these foals be humanly euthanized, but it is very important to know for sure that a white foal is in fact a Lethal White because white foals can be born that are totally healthy and normal. These would be horses with the maximum expression of their particular pattern or several patterns on the same horse.

Frame is designated by "Fr". Since it is dominant, the first letter is capitalized. Since there are two locations for a gene the other space must be filled up with something. In the case of heterozygous individuals the lower case letter is used indicating the gene is not present. All horses that have the Frame pattern have it genetically symbolized by "Frfr". With "Fr" being the gene that makes the horse Frame, or the dominant form of Frame. "fr" is the other half of the genetic code at that particular locus and only indicates that the Frame gene is present in one dose. By using a Punnet Square, it's very easy to figure out the what the chances are of producing a OLWS foal when two Frame horses are bred.