Final answer:
Crusted hyperkeratosis in Zn-responsive dermatosis is typically caused by genetic factors that affect zinc metabolism, leading to a deficiency of this vital mineral for skin health.
Step-by-step explanation:
The cause of crusted hyperkeratosis in Zn-responsive dermatosis is not due to excess oil production, zinc toxicity, or allergies. Rather, it is most often related to genetic factors that affect the absorption and metabolism of zinc in the body. Zinc is a vital mineral necessary for many biological functions, including skin health. When animals, especially dogs, have a genetic mutation affecting zinc absorption or metabolism, they can develop zinc-responsive dermatosis. This dermatologic condition manifests as crusted hyperkeratosis, typically on areas such as the face, paws, and around the eyes or mouth. Treatment usually involves dietary supplementation of zinc.