Parakeratosis is a skin disease of pigs caused by zinc deficiency, characterised by thickened, crusty, parakeratotic lesions, particularly on the legs, snout, and ears, with poor growth and rough hair coats. It became prominent when intensive pig production moved to high-calcium, plant-protein diets rich in phytate, which binds zinc and blocks its absorption. The condition was historically important in animal nutrition science because it demonstrated zinc’s essentiality and the practical impact of mineral interactions in feed formulation. Supplementing pig diets with zinc oxide or zinc sulphate prevents and cures it rapidly. Beyond veterinary interest, porcine parakeratosis helped establish principles that apply to human nutrition: phytate in unleavened wholegrain diets similarly impairs zinc absorption in people, contributing to deficiency in populations dependent on such staples.