IP stands for Incontinentia pigmenti - it is a dominant disease.
IP causes skin lesions soon after birth that develop into warty areas with hair loss. Wooley hair may grow back in these areas. Affected horses have streaks of light and dark coat color from birth. (may be mistaken for a color pattern because affected animals have a striped appearance resembling the brindle pattern in dogs) In addition, there are abnormalities of tooth, hoof, and eye development.
Only affected mares have been observed; affected males die before birth. Affected mares also have trouble with aborting foals.