Solid White Filly
White horses have a special place in the human imagination. Held sacred by many ancient cultures, they still bring to mind images of Pegasus and unicorns. The reality is a bit more mundane although the coloring is still striking. Most of the "white" horses seen in movies and TV are not in fact not white but completely grayed out or light cremellos or perlinos. The same is true for the Lipizzaner Stallions, although they are no less majestic. Since gray horses have dark skin and Cremellos and Perlinos both have some coloring in the hair (and sometimes skin), neither are truly white.
True white horses are fairly rare. White horses lack pigment and their coloring (or lack thereof) is due to white mutations. They are essentially one giant white spot. Their skin is pink and their hair is white not just lightly colored. Their eyes can be dark or blue and they will often have small spots of color around he eyes or ears. When all white is caused by a single gene mutation (such as W2 in thoroughbreds), it is easily inherited and generally does not come as a surprise, but when an all white foal is born from parents with "normal" or minimal white it can be quite a shock. When this occurs usually Lethal White Overo should immediately be considered and either ruled out or confirmed (more on Lethal White). However, Lethal White Overo and the White Spotting mutations are not the only things that can cause an all white horse. White horses can result from a combination of white patterns. When an all white foal is born in this scenario, it is general not reliably repeatable both because the white patterns are inherited separately, and because white pattern expression is highly variable. Even among horses that are identical genetically (ie clones) white markings vary considerably. Frame, Tobiano, the Splashed White patterns, and some of the White Spotting mutations can be involved in creating an all white foal. Usually 3 of the patterns are needed but not always.
This filly, born was born in 2019. Her sire is Hollywood Cool Gun (Hollywood Cool Gun's Facebook Page) and her dam is a Chestnut Tobiano mare named Flying Zoe. Her coloring (or lack of coloring) is due to a combination of Splashed White 1 and 2 and also Tobiano. She has a small amount of color around her eyes but otherwise is completely white. Because white pattern expression is highly variable, there is no guarantee that other horses with the same patterns will also be complete white. However, it does seem that horses horses that carry both Splashed White 2 and Tobiano do tend toward high white expression. Add splashed white 1 or Frame into the mix and the chances of an all white foal increase even more. This filly does not carry Frame at all and therefore can never produce a Lethal White Foal.
All photos are courtesy of Sue Williams