SWO stands for Splashed White Overo - it is a recessive disorder
SWO is another coat pattern defect - it applies to patterns that determine white. Embryos that receive two of these genes will not complete development and will abort in the womb.
Hearing loss is associated with White Patterned horses - horses white on the inside of the ear are affected - horses who's ears have pigmented hair inside the ear are not affected.
Splashed White 2 (SW2) and Splashed White 3 (SW3) are found Quarter Horses and related breeds.
Genetic Codes:
| SW1/SW1 | Homozygous | Horse has two copies of the SW-1 mutation |
| N/SW1 | Heterozygous | Horse has one copy of the SW-1 mutation |
| N/N | Negative | No copies of SW-1 mutation |
| SW2/SW2 | Homozygous | Horse has two copies of the SW-2 mutation |
| N/SW2 | Heterozygous | Horse has one copy of the SW-2 mutation |
| N/N | Negative | No copies of SW-2 mutation |
| SW3/SW3 | Homozygous | Possible homozygous lethal |
| N/SW3 | Heterozygous | Horse has one copy of the SW-3 mutation |
| N/N | Negative | No copies of SW-3 mutation |
| SW4/SW4 | Homozygous | Possible homozygous lethal but no current information available |
| N/SW4 | Heterozygous | Horse has one copy of the SW-4 mutation |
| N/N | Negative | No copies of SW-4 mutation |