Final answer:
The disease causing separation between superficial and deep skin layers in horses, leading to 'stretchy' and easily damaged skin, is Hereditary Equine Regional Dermal Asthenia (HERDA), primarily seen in Quarter Horses.
Step-by-step explanation:
The separation between the superficial and deep layers of skin resulting in 'stretchy' skin easily damaged or torn in horses is characteristic of Hereditary Equine Regional Dermal Asthenia (HERDA). This disease primarily affects Quarter Horses and is due to a genetic defect that impacts the collagen in the skin, which makes the dermis and epidermis lack the proper adherence, leading to the symptoms described. Unlike conditions in humans such as pseudoxanthoma elasticum or systemic lupus erythematosus which affect multiple systems, HERDA specifically affects the horse's skin integrity.