Frame Overo (Also called simply "Frame" or "Overo") is a pattern of spotting created by the "Frame" gene
Both The University of California at Davis and Animal Genetics, Inc. of Florida can test for the presence of Tobiano, Red, Frame, Creme, Silver, Sabino1, and Agouti (Bay). The test for Tobiano can determine whether or not a horse is homozygous of heterozygous (good to know if you are trying to breed for Tobiano).
You can download forms for these tests from their website-- follow
OR, from the Animal Genetics website
Other Spotting Patterns:
OVERO LETHAL WHITE SYNDROME:
Overo Lethal White Syndrome is the result of an embryo that is homozygous for the Frame Overo gene. A single Frame Overo gene creates the very striking and popular Frame Overo pinto pattern, but when doubled up, the foal's intestinal system does not develop properly, and the foal dies within 72 hours of birth, when it is unable to digest its first meals. To date, there is no surgery or other treatment to save these unfortunate foals.
The way to avoid this tragedy is simply to avoid breeding Frame to Frame. The hard part is identifying carriers of this gene. There are many color patterns that resemble Frame Overo (Many loud Sabinos look very much like Frames, for instance), and others that mask it. Frame is sometimes very minimally expressed, so that the horse does not appear to be a Frame at all, but only a "normal" horse with pretty socks or a nice wide blaze, etc. (This is the most likely explanation for the so-called "crop-pouts" that occur in some of the non-color breeds) Frame Overo is attractive and highly prized by horse owners. The challenge is breeding for it safely.
A laboratory test using a simply-obtained hair sample is now available at UC Davis, that will help avoid this tragedy by identifying carriers, so that they may be bred safely. Since horses can carry the Frame gene without it being expressed to a recognizable degree, it is a good idea to have all breeding stock tested for this gene.
You can download forms for this and other genetic tests from the UC Davis website-- follow the links from http://www.vgl.ucdavis.edu
The American Paint Horse Association makes no distinction between the 3 types of overo: Splash, Frame, and Sabino. We know that the other Overos - Splash and Sabino - are not connected to Overo Lethal White Syndrome.
It is also possible for sabinos and splashed overos, solid colored horses, and apparent Tobianos to carry Frame "silently" (not obvious by appearance) and thus be capable of producing a lethal white foal.
UC Davis says: "The gene appears to be associated with horses often characterized as "frame-overos" in Paints and Thoroughbreds, but is also present in some tobiano/overos, some solid-colored (breeding stock Paint) offspring from overo matings, some tobianos and Quarter Horses without obvious evidence of the overo pattern. The gene has also been identified in an overo Miniature Horse...We know of no other mutations that are associated with lethal white overo horses. However, owners requesting the diagnostic test should understand that there is the rare possibility that two NN horses could have a lethal white foal due if both the sire and dam carry a mutation at a site other than the one detected by this test. "
|Overo, for registration purposes in the American Paint Horse Association Registry, includes all pinto patterns that are not clearly Tobiano: Frame, Sabino, Splashed White, Tovero, and anything else. This makes sense, in that the patterns can be hard to distinguish from one another, but their genetics are entirely separate.
Lumping them together can be extremely frustrating when trying to use pedigrees to trace color genetics. Each of these patterns have their own genetics, and only Frame Overo carries with it the risk of Overo Lethal White Syndrome. In this website, each pattern is considered separately.
FRAME: UNIQUELY AMERICAN!
Dr. Phil Sponenberg says this about the Frame Overo pattern: "The frame overo pattern is especially interesting, since it is almost limited to North American Colonial Spanish horses or their descendants. From that origin the color pattern has spread to other regions and breeds, but all evidence points to it being a Spanish pattern originally. Different breeders select for various of these colors and patterns, but all can be shown to have been present in the Spanish horses at the time of the conquest."
Lewella Tembreull, a modern-day expert in color genetics, believes instead that Frame is a mutation that occured in North America, after the Spanish reintroduced them: " That was Sponenberg's theory but Frame does not occur in any breeds that are not North or South American in origin. I believe Sponenberg originally published the ... theory prior to the existence of Frame/LW testing. If Frame/LW existed in European breeds we'd be seeing LWO foals from those breeds as well as positive test results and we just aren't. The only breeds that produce LWO foals and LWO+ test results are American breeds.
GENETIC ROULETTE FOR BREEDERS
LW and LWO and OLWS in the above quote all refer to "Overo Lethal White Syndrome" - a fatal condition of foals who are homozygous for the Frame gene. A single Frame gene can create magnificant pinto patterns - or be carried almost silently. But when two horses, each carrying one Frame gene, are mated, 25% of offspring will be born pure white, or nearly so, and will die within a few days of birth due to an incomplete digestive tract. Complicating this issue is Sb1, one of the Sabino patterns, that can look very much like Frame, and can produce a white or nearly all white foal that is perfectly normal.
There are several labs throughout the United States that can test for Frame at a very reasonable cost. Anyone considering breeding horses of American origin (regardless of whether or not they show the frame pattern) should have their breeding stock tested, to avoid accidental doubling up on the Frame gene.
Nadine Wawrzyniec's buckskin frame overo mare
FRAME OVERO CHARACTERISTICS:
She was genetically tested and is Frame (LWS) positive (N/O), but negative on Sabino1 (N/N). But it could be that she has one of the as of yet unidentified Sabino genes.
Her name is Spectaculare. She is registered Oldenburg. Her mom is a Medicine Hat Tovero, registered PtHA.