This type of ‘marking’ is not a genetic thing, or even a rare marking thing. While it is rare, it’s caused by something that doesn’t take geneticists to figure out. These animals have been affected by some sort of a fungal infection that damaged hair follicles. Often, when a horse is injured, their hair will regrow without pigment, giving them white patches in addition to a scar. The same seems true when anything affects a hair follicle’s mechanical ability to produce pigment.
Mistaken Identity
These types of marking can be (and probably often is) easily be mistaken for something else. As they don’t necessarily come from one source, they very considerably and can look suspiciously like appaloosa or even pinto patterns. Sadly it seems that animals with this type of spotting could be cast aside from breeding programs because they could not pass it along to their offspring.
Example Notes
There is not much information online about the regrowth of hair after an equine fungal infection, but the animals pictured below don’t seem to match the criteria for other types of rare markings. The first image of a bay with marks along its spine may be injury related, however the splotches and almost brindling up the side make us think there may be more involved. The second and third images could be birdcatcher spots, but they are usually more round, defined and evenly distributed. The final image is likely the cause for some of the others, as it looks like an active fungal infection in an older animal. Notice the similar patterning of white marks in the chestnut and the affected area in an infected animal.
