Have you ever heard of them? I hadn’t, but we’ve all seen them. Whether we knew what they were or not.
These lines will appear as marks in the coloring, other times as lines in the hair growth, stripes across the rib cage or neck. In most animals they are not visible, but occasionally they will show up when color, or hair growth, organizes along the lines. They will often be seen on horses with extreme rabcino markings or varnishing in Appaloosas. “Brindle” horses are often just horses with a concentration of roan, sooty, or grey along the the lines
These lines, which occur on humans as well as horses, represent the developmental growth pattern of the skin. Blaschko lines are thought to represent pathways of epidermal cell migration during the development of the fetus.
The lines themselves are invisible, but in humans many inherited and acquired diseases of skin and disorders of hyperpigmentation show along these patterns giving a visual appearance to these lines. In horses, with more colorful coat colors available, they can change the way the coat color presents. Unfortunately the color itself will not pass on genetically.
In horses the lines of blaschko can come and go throughout the horse’s life time, when they appear as lines in the hair. One theory is that lymphatic drainage can cause the lines to appear. Although the lines do not correspond to any known nervous, vascular or lymphatic structures or fascia.
They will show up after a message or an event in the horses life that was apparently stressful or in some way extreme for the horse. That would seem to be a sign that they can be related to something going on within the horse.